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Behaviour underpins many facets of the performance of animals in aquaculture. By manipulating culture systems to segregate or allow particular aspects of conspecific interaction, we found physical interactions between P. ornatus individuals to be essential for better culture performance. Three culture types were used to control conspecific interactions: isolated culture (individual vessels) excluded all conspecific interactions, separated culture (lobsters cultured in adjacent cages) excluded physical interactions, and communal culture allowed for all interactions. Two water exchange rates were introduced to investigate the influence of chemical cue intensity on growth and survival. Time-series photography was used to determine the feeding behaviour and preference for different feeds including mussel gonad, commercial prawn feed and moist feed. The experiment showed improved growth and moulting frequency in communally cultured lobsters. These results suggest that direct physical contact between conspecifics is required to optimise growth of lobsters, which may be related to the complex social structures of this gregarious species. Behavioural observations of two juvenile instars (2 and 4), revealed circadian rhythm of interactions with feeds, feed preferences and intake. Observations revealed differing behaviours between the different culture types, where lobsters reared in separation displayed higher level of interactions with feeds; however this was not associated with higher feed intake. Observations of two juvenile instars (2 and 4) exhibited increase of daylight activity (interactions with feeds and feed intake) in older lobsters (instar 4).

Research with a variety of aquatic ectotherms suggests that variation in individual metabolic rate (i.e., metabolic phenotype) can be a factor that influences the behaviour and growth of individuals. Slow growth, growth disparity and growth depensation have been reported as major drawbacks to spiny lobster production which is thought to be associated with agonistic behaviour of dominant individuals controlling a disproportional share of food resources. Our study examined the relationship between individual variation of metabolic phenotypes (standard, routine and active metabolic rates and aerobic scope), and growth performance of juvenile spiny lobster, Sagmariasus verreauxi (5.99 ± 0.46 g) that were reared either individually (n = 20) or communally as a group of 20 for 90 days. Growth performance and feed intake were significantly higher in communal rearing demonstrating that social interaction is important for promoting growth of spiny lobsters. There was a positive relationship between standard metabolic rate, routine metabolic rate and growth in individually reared lobsters indicating a direct link between metabolic phenotype and growth of lobsters in the absence of social interaction. There was no relationship between metabolic phenotype and growth in communal rearing suggesting that social interactions outweigh the direct link between metabolic rate and lobster growth. The results demonstrate for the first time that growth performance of spiny lobsters can be linked with individual variation in metabolic status however social behaviour plays a more dominant role in determining growth of this naturally gregarious species.

As salmon aquaculture continues to grow, understanding aquafeed conversion is imperative for making informed strategic growth planning and management decisions. Accurately measuring the apparent digestibility (AD) of commercial aquafeeds on farms requires greater understanding and method development, including the validation of one or more inert endogenous AD markers. Laboratory and commercial experiments assessed the potential of elements that naturally occur in aquafeeds as potential endogenous AD markers. Two commonly used and validated AD markers, acid insoluble ash (an endogenous marker) and ytterbium oxide (an exogenous marker) were compared using protein AD calculated from a range of endogenous elements. Using a Percentage Similarity Analysis, comparison of protein digestibility calculated with recognised AD markers demonstrated lutetium (Lu) was the most accurate endogenous AD marker. Identification of Lu as an effective endogenous AD marker in commercial salmon aquafeeds will facilitate straightforward measurement of AD under commercial conditions. This work has important application in salmon aquaculture where protein AD is fundamental to growth efficiency.

One of the main challenges for spiny lobster aquaculture is the successful development of formulated feeds that are attractive, readily consumed by lobsters and promote optimal growth and survival. In a 54-day growth trial, we investigated the performance of four moist formulated feeds containing A) non-homogenised flesh ingredients; B) fish meal only; C) 10% krill meal; or D) homogenised flesh ingredients; and a reference diet of shucked blue mussel (Mytilus galloprovincialis) flesh, on growth, nutritional condition and feeding behaviour of juvenile tropical spiny lobster (Panulirus ornatus) reared either communally or individually. Growth and survival achieved by lobsters fed mussel were significantly higher than all other treatments. However, lobsters fed the formulated feed containing 10% krill meal (treatment C) and reared communally had a significantly higher growth, survival and feeding performance when compared to the formulated feeds with inclusion of non-homogenised and homogenised flesh ingredients (treatments A and D). The highest levels of feed interaction and pellet consumption among the formulated feeds were also recorded for treatment C. We demonstrated that the inclusion of krill meal in formulated feeds provides a benefit when compared to the inclusion of the flesh ingredients. Flesh ingredient format (homogenised or non-homogenised) had no effect on growth performance of lobsters, suggesting that the process of homogenisation of flesh ingredients does not provide any benefit in promoting feed consumption. Furthermore, time-series photography analysis trials showed that all the formulated feeds only promoted a feeding response within the first 2–3 h post-feeding, whereas mussel retained its attractiveness throughout the feeding period. These results suggest that the prolonged attractiveness remains an impediment for formulated feed performance in lobster culture. The present study also showed that growth performance and feeding response were higher in lobsters reared communally than individually. As observed in other spiny lobster species, it is likely that social interactions in communal housing may have provided cues that stimulated feeding responses and promoted higher growth rates.

Understanding the molecular mechanisms that underlie differences in feed efficiency (FE) is an important step toward optimising growth and achieving sustainable salmonid aquaculture. In this study, the liver and white muscle proteomes of feed efficient (EFF) and inefficient (INEFF) Chinook salmon (Oncorhynchus tshawytscha) reared in seawater were investigated by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In total, 2746 liver and 702 white muscle proteins were quantified and compared between 21 EFF and 22 INEFF fish. GSEA showed that gene sets related to protein synthesis were enriched in the liver and white muscle of the EFF group, while conversely, pathways related to protein degradation (amino acid catabolism and proteolysis, respectively) were the most affected processes in the liver and white muscle of INEFF fish. Estimates of individual daily feed intake and share of the meal within tank were significantly higher in the INEFF than the EFF fish showing INEFF fish were likely more dominant during feeding and overfed. Overeating by the INEFF fish was associated with an increase in protein catabolism. This study found that fish with different FE values had expression differences in the gene sets related to protein turnover, and this result supports the hypothesis that protein metabolism plays a role in FE.

Apparent digestibility and gastrointestinal evacuation rate were measured to assess the potential of five commercially available protein sources for their inclusion in feeds for juvenile slipper lobster, Thenus australiensis. Protein sources tested were fishmeal, krill meal, lupin meal, soybean meal and squid by-product meal. Apparent digestibility of crude protein ranged from 79.6% to 95.3%, with fishmeal protein significantly less digestible than lupin meal, squid by-product meal and soybean meal. Gastrointestinal evacuation rate was estimated from marker replacement, where yttrium oxide replaced ytterbium oxide. Faeces were collected every 3 h for 48 h, and a kinetic model was used to calculate the rate and time for the second marker to replace the first marker. Gastrointestinal evacuation (≥ 95%) was completed between 4 and 6 h with no significant differences among protein sources. Faeces consisted of both markers in equal parts 2.7 to 5.0 h after the feed switch, with lupin meal reaching the midpoint significantly faster than squid by-product meal and reference feed. The present study is the first in crustaceans to examine the relationship between apparent digestibility and gastrointestinal evacuation, showing more digestible protein sources had slower evacuation rates. The combined approach provides deeper insight into crustaceans' digestive physiology and helps understand their ability to digest specific ingredients. Further research is recommended to understand protein requirements in a broader context to verify highly digestible protein sources meet all nutritional requirements.

Feed ration plays a crucial role in influencing fish growth performance and maintaining optimal gut health over the seasonal temperature range. However, we have limited knowledge of how these factors affect the gut microbiota of Chinook salmon (Oncorhynchus tshawytscha) farmed in freshwater recirculating aquaculture systems (RAS). Here we examined the environmental and faecal microbiota of freshwater Chinook salmon using 16S rRNA gene V1-V3 amplicon sequencing and evaluated the relationship between faecal casts and dominant microflora. Faecal microbial communities were highly stable in terms of composition and diversity regardless of feed ration and temperature changes, whereas temperature significantly affected water microbiota. The composition of faecal microbiota significantly differed from the microbiota of water or feed. The faecal microbiota was dominated by the species Photobacterium piscicola that was more predominant in faecal samples with higher water content (high faecal scores). The relative abundance of lactic acid bacteria (LAB) in the gut was distinctly lower than that in the feed and water. Our study provides detailed information on the complex microbial communities in the freshwater RAS and farmed Chinook salmon. It increases our knowledge of potential linkages between core gut microbiota and gut health, illustrated by the relationship between faecal casts and dominant microflora, and provides useful information for sustainable land-based Chinook salmon aquaculture.

Phospholipids , especially phosphatidylcholine (PC), are considered essential nutrients for larval and juvenile stages of many decapod crustacean species due to low rates of endogenous biosynthesis and potential nutritional benefits in assisting lipid digestion and transport. This study was conducted to test the hypothesis that dietary PC is essential and would subsequently have beneficial effects on lipid utilisation and digestibility of fish oil triacylglycerol (TAG) in the slipper lobster, Thenus australiensis. Juvenile slipper lobsters were supplied six formulated experimental feeds with actual PC contents of 0.05, 0.48, 0.65, 0.98, 1.15 and 1.43% (dry matter) for 12 weeks. Manipulating dietary PC content had no effects on survival, growth, chemical composition, whole body or tissue lipid distribution, or apparent digestibility (AD) of gross energy (GE), total lipid (TL) or PC. Juvenile slipper lobsters appeared to possess fully developed and efficient mechanisms for GE, TAG and PC digestion (>95% AD). In vivo lipid class mass balance calculations demonstrated net intake of TL and TAG was considerably greater than was accumulated in the whole-body during growth. Thus, a significant proportion of dietary TL and TAG was utilised for energy and other metabolic processes. In contrast, particularly for low PL dietary treatments (≤ 0.5%), net gain of PC was greater than net intake, indicating a reliance on biosynthesis of PC. Thus, it is concluded that there is no or a very low requirement for dietary PC and thus may not be essential for the examined size class of juvenile T. australiensis when supplied adequate dietary PC biosynthetic precursors and other potentially related dietary nutrients. Further targeted research is recommended to verify if these findings are applicable to larval and early juvenile stages, and to enhance overall understanding of lipid nutritional requirements for T. australiensis.

Feed efficiency, the relative ability to convert feed nutrients into growth, is an important factor in the primary production of animals. Farming fish with improved feed efficiency is necessary to reduce production costs and achieve sustainability for the aquaculture industry. Proteomics provides an approach to discover biochemical mechanisms driving feed efficiency. To do this, we have evaluated the proteomic profile of liver and white muscle in efficient (EFF) and inefficient (INEFF) Chinook salmon (Oncorhynchus tshawytscha). Twenty-six fish, 14 EFF and 12 INEFF individuals, were assessed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and a data-independent acquisition method. In total, 2433 liver and 635 white muscle proteins were quantified across all samples. Bioinformatics showed enrichment of gene ontology (GO) terms related to lipid metabolism in liver of EFF fish (~30% of total GO terms). Protein metabolism (~30% of total GO terms) were the top enriched pathways in white muscle of EFF fish. In INEFF fish, protein processing in endoplasmic reticulum and proteolysis (~40% of total GO terms) were the highest enriched GO terms in the liver. This is the first study to compare feed efficient and inefficient individuals at the proteomic level in an aquatic species and the results provide a preliminary insight into the fundamental molecular landscape of feed efficiency in Chinook salmon.

The spiny lobster Sagmariasus verreauxi is an emerging lobster species for intensive aquaculture. The lack of any nutritional information required for feed development in this species initiated this study to understand the effect of different dietary lipid sources on tissue lipid profiles and expression of selected lipid metabolising genes. Krill oil, marine oil (blend of fish oils), and vegetable oil (combination of linseed and palm oil), were utilised to formulate three experimental feeds with different phospholipid, triacylglycerol and polyunsaturated fatty acid profiles. Experimental feeds were administered to freshly moulted juvenile S. verreauxi for 50 to 55 days, to determine the effect of lipid sources on the nutritional status, fatty acid composition and expression of genes related to fatty acid biosynthesis, β-oxidation, lipid catabolism and regulation of lipid metabolism. While there were no significant differences in terms of weight gain and mortality among different dietary treatments, the fatty acids composition in the hepatopancreas and to some extent, muscle tissues correlated with the fatty acids composition of the respective dietary treatments. Vegetable oil diet resulted in higher expression of genes related to β-oxidation, which indicates selectivity towards utilisation of monounsaturated fatty acids for energy in this species. In tandem, genes related to fatty acid and cholesterol biosynthesis were upregulated, suggesting their importance in the marine lobster diet. This is the first report on the use of formulated feeds to successfully maintain juvenile S. verreauxi.

There is currently renewed interest in farming triploid Atlantic salmon. Improving farming requires identifying triploid specific phenotypic and physiological traits that are uniquely derived from ploidy per se and developed under optimal growing conditions. This study investigated firstly, the impact of ploidy on growth performance and whole body composition of Atlantic salmon at different early freshwater stages [34 dph (days post-hatching) alevin, 109 dph fry, and 162 dph parr] and secondly, whether phenotypic differences at these stages were reflected in protein samples collected from whole fish, white muscle or liver tissue. Female diploid and triploid Atlantic salmon (n = 3) were first fed at 35 dph and then maintained by feeding to satiation on commercial feeds. Triploids were significantly lower in weight at the late alevin and fry stages but matched diploid weight at the parr stage. The whole-body lipid content was significantly higher for triploids at the parr stage, while the whole-body lipid class profile was broadly similar and was largely not affected by ploidy. Comparative label-free shotgun proteomic analysis did not detect significant alterations in protein expression between diploids and triploids at any growth stage. The present results indicate that ploidy under optimal growing conditions and during early freshwater stages only result in small phenotypic differences in weight and whole body lipid content that were not reflected at the proteome level. These findings suggest that optimal husbandry conditions for freshwater Atlantic salmon are similar between ploidies, at least for all-female populations.

We examined the effects of temperature on the growth, feeding, nutritional condition and aerobic metabolism of juvenile spiny lobster, Sagmariasus verreauxi, in order to determine if temperature acclimated aerobic scope correlates with optimum for growth and to establish the thermal tolerance window for this emerging aquaculture species. Juvenile lobsters (initial weight = 10.95 ± 0.47 g) were reared (n = 7) at temperatures from 11.0 to 28.5 °C for 145 days. All lobsters survived from 14.5 to 25.0 °C while survival was reduced at 11.0 °C (86%) and all lobsters died at 28.5 °C. Lobster specific growth rate and specific feed consumption displayed a unimodal response with temperature, peaking at 21.5 °C. Lobster standard, routine and maximum metabolic rates, and aerobic scope all increased exponentially up to maximum non-lethal temperature. Optimum temperature for growth did not correspond to that for maximum aerobic scope suggesting that aerobic scope is not an effective predictor of the thermal optimum of spiny lobsters. Plateauing of specific feed consumption beyond 21.5 °C suggests that temperature dependent growth of lobsters is limited by capacity to ingest or digest sufficient food to meet increasing maintenance metabolic demands at high temperatures. The nutritional condition of lobsters was not influenced by temperature and feed conversion ratio was improved at lower temperatures. These findings add to a growing body of evidence questioning the generality of aerobic scope to describe the physiological thermal boundaries of aquatic ectotherms and suggest that feed intake plays a crucial role in regulating performance at thermal extremes.

Simultaneous measurements of nitrogenous (ammonia and urea) excretion and respiratory gas (O2 and CO2) exchange provide a non-destructive stoichiometric bioenergetic approach to elucidate metabolic energy substrate use which has rarely been used with aquatic ectotherms due to previous difficulties in measuring total CO2 excretion. This study examined metabolic energy substrate use and specific dynamic action (SDA) in cultured spiny lobster, Sagmariasus verreauxi, of different nutritional status. SDA magnitude calculated by stoichiometry was compared to a traditional composite oxycalorific coefficient approach. Protein synthesis can account for a large part of SDA in aquatic ectotherms. This study used a protein synthesis inhibitor cycloheximide to investigate the contribution of cycloheximide-sensitive protein synthesis to SDA and the effect of cycloheximide on nitrogenous and CO2 excretion. Lobsters were subjected to five treatments: 2-day fasted juveniles sham injected with saline (FS treatment); 2-day fasted juveniles injected with cycloheximide (FC treatment); 10-day starved juveniles injected with cycloheximide (SC treatment); post-prandial juveniles fed squid Nototodarus sloanii (FED treatment) and; post-prandial juveniles injected with cycloheximide (FEDC treatment). Protein was the primary energy substrate (65% of oxygen consumption) for 2-day fasted juveniles, with lipid accounting for the remainder (35%). After 10-day starvation lipid became the main substrate, indicating lipid oxidation increased with extended fasting. Following feeding, protein contribution remained above 50%, while lipid (0–43%) and carbohydrate (0–37%) provided significant energy at different time periods, indicating besides protein appropriate proportions of non-protein ingredients are also essential to lobsters. SDA magnitude in FED and FEDC treatments estimated by the traditional approach was 10.5 and 0.4 J g−1, respectively, indicating S. verreauxi expended 96% of post-prandial energy on protein synthesis and that decapod protein synthesis can account for one of the highest proportions of SDA in aquatic ectotherms. SDA magnitude in the FED treatment evaluated by stoichiometry (12.6 J g−1) was comparable to the traditional approach. Interestingly, stoichiometry was not applicable in the FEDC treatment as the respiratory quotient exceeded the theoretical maximum under aerobic conditions. Cycloheximide did not affect CO2 excretion among all treatments or nitrogenous excretion among unfed treatments, while the post-treatment total nitrogenous excretion reduced in fed lobsters. The combined measurement of substrate use and SDA potentially helps optimize the feed to achieve sustainable aquaculture. However, more research is required to decipher limitations and the applicability of stoichiometry for crustaceans.

Following recent advances in hatchery technology and large-scale larval rearing of spiny and slipper lobsters, a greater understanding of key nutritional requirements is now imperative to facilitate feed development for juvenile culture. However, there is a lack of relevant information available for the slipper lobsters, particularly Thenus species. This study sought to evaluate the potential requirements for and effects of a fresh ingredient component in a formulated feed on the growth performance of hatchery-reared juvenile Thenus australiensis. This was assessed using six formulated experimental feeds incorporating fresh blue mussel flesh (BM; Mytilus galloprovincialis) in a geometric series (0, 1.6, 3.1, 6.3, 12.5 and 25.0% dry matter) administered continuously over 9 weeks. An additional dietary treatment of blue mussel half shells (BMHS) was included as a reference feed to establish a benchmark of growth potential. Survival and moult frequency were unaffected by feed treatment. Lobsters fed BMHS displayed a clustered or synchronised moulting pattern with two major moulting events lasting several days each during the experiment. In contrast, lobsters provided experimental feeds moulted continuously throughout the experiment. The BMHS produced approximately 2-fold greater growth compared to experimental feeds, while BM incorporated into experimental feeds had no beneficial effect on growth at any inclusion level. Growth mirrored feed intake where it was also found that feed intake on a dry matter basis was approximately 2-fold higher for BMHS compared to experimental feeds, while biological feed conversion ratios were similar for all feeds. Thus, dry matter intake appeared to be primarily responsible for the difference in growth rates achieved. Bulk chemical analysis revealed that BMHS-fed lobsters had significantly lower ash content coupled with higher gross energy, total lipid and polar lipid contents on a proportional basis compared to lobsters fed formulated experimental feeds. Lobster haemolymph Brix values were also significantly higher in the BMHS treatment lobsters. Higher Brix coupled with decreasing feed intake suggests these lobsters were on average at a more advanced stage within the moult cycle and offers a possible explanation for differences in body chemistry. In conclusion, while growth rates were lower in animals fed formulated feeds compared to benchmark growth performance, overall survival, moulting and growth performance revealed the potential of the basal experimental feed formulation as a reference for future nutrition research with this species without a requirement for inclusion of fresh BM. The research highlights that significant opportunities exist to improve slipper lobster growth performance through maximising feed intake.

The moult cycle is arguably the most critical aspect of crustacean biology and is associated with dramatic changes in behaviour, physiology and condition. Here we describe the first detailed investigation of the combined changes in morphology, physiological status and nutritional condition over the moult cycle of juvenile T. australiensis. Haemolymph refractive index (measured as Brix) was evaluated as a non-destructive method for predicting physiological status and nutritional condition. Post-moult, inter-moult and pre-moult stages were identifiable by microscopic examination of the pleopod distal tips, though differentiation of the pre-moult substages was not possible using this technique. Monitoring of ecdysial suture lines on the exoskeleton gill chambers was found to be highly useful for visually determining progression through the pre-moult stage and predicting the timing of ecdysis. A classical pattern of inter-moult growth was observed where size and wet weight remained relatively uniform over the moult cycle while highly significant changes in whole-body composition were simultaneously observed over time. Growth was most evident by changes in dry weight and dry matter content which more than doubled by the onset of pre-moult. Changes in dry matter content were generally mirrored by Brix and whole-body crude protein, total lipid and gross energy content. Brix strongly correlated with dry matter content and significant correlations were also found for all other primary measures of nutritional condition. Typical moult-related changes were also found for circulating ecdysteroids. This study clearly demonstrates pronounced cyclical changes in physiology and condition of juvenile T. australiensis over a typical moult cycle. The significant correlations between haemolymph and whole-body composition validates Brix as a practical and non-destructive method to objectively assess physiological status, nutritional condition and quality in T. australiensis and further demonstrates its potential for individual crustacean assessment in experimental research and practical commercial applications.

Detailed classification and characterisation of the gut microbial community and understanding of factors affecting the microbiota are essential to understand the relationship between Chinook salmon (Oncorhynchus tshawytscha) gut microbiota and fish health. Here we evaluated the multiple effects of biotic and abiotic factors on the gut microbial community composition of farmed Chinook salmon, based on high-throughput sequencing of 16S rRNA gene V1-V3 amplicons. Gastrointestinal microbial community composition was highly dynamic between freshwater and saltwater conditions but similar among individual fish. A high abundance of Proteobacteria and a relatively low abundance of lactic acid bacteria (LAB) were detected in farmed Chinook salmon regardless of salinity. Species richness and diversity were significantly higher in freshwater farmed salmon than in those farmed in the marine environment. Water temperature and farming location displayed relatively minor effects on gut microbiota, while fish age had significant effects on the beta diversity of gut microbiota in both freshwater and saltwater habitats. Our study provided a detailed description of the gut microbial community of farmed Chinook salmon during grow out and contributed to a greater understanding of the effects of fish age and water salinity on the gut microbiota modulation.

Understanding the nutrition of lobster larvae through the examination of growth and biochemical composition across different life stages is a critical component of aquafeed development of new aquaculture species. Therefore, in the present study, we benchmarked growth and changes in biochemical composition of Thenus australiensis from first larval stage (S1) to the juvenile first stage (J1). The larval cycle was completed in a maximum duration of 31 d and comprised four successive larval stages followed by a post-larvae stage (nisto) and a subsequent moult to J1. Growth during all larval stages, metamorphosis to nisto, and moult to J1 were tracked through the measurement of size (total length, TL and cephalic/carapace width, CW), individual wet (WW) and dry (DW) weights. Bulk samples of all developmental stages were collected and analysed for ash, crude protein, total lipid, nitrogen free extract (NFE) and gross energy of dry matter (DM). Lipid class, fatty acid and mineral composition of S1, S4 and J1 of DM were also measured to provide more detailed analysis of composition. As expected, TL, CW, WW and DW increased with each subsequent stage except for lower TL and CW of the nisto stage when compared to S4 larvae. The DW increases throughout larval development until nisto and was defined by higher ash, crude protein, total lipid and NFE absolute amounts. However, from nisto to J1, total lipid decreased by half. The total lipid of DM increased as larval stages progressed to the nisto phase, declining rapidly when monitored at J1. The accumulation of lipid during the larval phase highlights the importance of building lipid stores to maintain metabolism during the non-feeding nisto stage and moult to J1. Polar lipid was the dominant lipid group in comparison to neutral lipids stores. The energy content of larvae, nisto and J1 reflected the accumulation of lipid over the larval stages and its depletion during the non-feeding nisto stage. The environmental influence on elemental uptake was evident at the moult to J1 with a >4-fold increase in ash content in individual J1 compared to nisto. This was supported by an increase of major mineral constituents of the exoskeleton, particularly, calcium. The present study is the first describing in detail the growth and biochemical composition of all the larval stages until J1 for T. australiensis. The new knowledge on nutrition will support progress in aquafeed development for this new aquaculture species.

Farmed Atlantic salmon in Tasmania are exposed to elevated water temperatures during summer, which is often associated with reduced pigmentation quality. This study tested the effects of the factors: temperature (elevated, 19.4 °C (ET) vs. control, 15.2 °C), dietary fatty acid (FA) composition (diet 1, high in fish oil vs. diet 2, low in fish oil) and fillet cut (anterior/dorsal cut; ADCT and dorsal Norwegian quality cut (dNQC)) on the concentration of astaxanthin (Axn) in white muscle of salmon post-smolt. After fish doubled initial weights (212 g) at each temperature, the concentration of Axn in muscle was not affected by dietary FA composition, but was higher at ET and higher in the dorsal NQC at ET. In contrast, Axn concentrations between these fillet cuts were the same at the control temperature. The concentration of long chain polyunsaturated FA, which are prone to peroxidation, was generally higher in the fish fed the diet high in fish oil, and in the anterior/dorsal cut. However, the relationships between these FA within triglycerides and phospholipids and the lipid peroxidation product malondialdehyde in white muscle were poor. Further, the concentrations of malondialdehyde showed a poor relationship with Axn in white muscle. There was no idoxanthin in any of the white muscle samples at the analytical detection limit of 0.1 mg/kg. In summary, ET led to higher concentrations of Axn in white muscle, but also to heterogeneous Axn concentrations between the fillet cuts tested. The concentration of Axn in white muscle was not affected by the dietary FA composition and was not associated with oxidative stress or metabolic conversion into idoxanthin in this tissue under the conditions tested. When Axn was expressed per unit of crude protein, the concentration of Axn was higher in the dorsal NQC at ET, indicating that differences of myofibrillar white muscle proteins in their capacity to bind pigment carotenoids may have contributed to the heterogeneous pigment deposition in fillet at ET. Global sea temperatures are anticipated to rise in the future and the implications for aquaculture production must be understood. This study demonstrated the significant effects of temperature on the deposition of pigment carotenoids over the fillet of salmon.

Pigment-depletion in the fillets of farmed Atlantic salmon (Salmo salar) arises after periods of elevated water temperatures with voluntary starving. This study tested the effects of dietary pre-loading with different pigment carotenoids (astaxanthin and/or canthaxanthin) combined with two α-tocopherol levels (normal and high: 500 and 1000 mg/kg, respectively) on pigment-depletion in vivo in Atlantic salmon after four weeks of challenge. We also tested whether oxidative stress manifested as an underlying depletion mechanism. Carotenoid levels in whole fillet homogenates were not decreased significantly post-challenge but fillet α-tocopherol concentrations were increased significantly in contrast to decreased oxidative stress indices. However, image analysis revealed localised fillet pigment-depletion following all dietary treatments. These data imply that localised pigment-depletion was not prevented by pre-loading of the fillet with different carotenoid-types/mixtures and increased of α-tocopherol levels from normal to high, respectively. Further, we suggest that oxidative stress might not facilitate pigment-depletion in vivo.

The ability of lobsters to recover from stress is an important factor influencing growth and survival in aquaculture; however, there is limited information on the metabolic responses of spiny lobsters to stress. This study determined oxygen consumption rate ( M ˙ O 2 ) and ammonia-N excretion of juvenile spiny lobsters Sagmariasus verreauxi in response to handling, anaesthesia, anaesthesia then force feeding, and exercising to exhaustion in order to determine the recovery time and amount of oxygen required to recover from common sources of stress in aquaculture. Lobsters required 0.29 ± 0.24 mg O2 g DM− 1 over a period of 2.5 ± 1.40 h to recover from handling. Anaesthesia with 2-phenoxyethanol immobilised lobsters but they required 0.72 ± 0.36 mg O2 g DM− 1 over a period of 4.5 ± 1.77 h to recover, indicating that 2-phenoxyethanol causes substantial stress. Force feeding lobsters anaesthetised with 2-phenoxyethanol or clove oil did not result in a higher increase of M ˙ O 2 compared to 2-phenoxyethanol anaesthesia alone. Recovery from exercise to exhaustion required 1.84 mg O2 g DM− 1 over a period of 10.17 ± 0.70 h. Ammonia-N excretion, measured 24 h post-treatment, and atomic O:N ratios were not significantly different between treatments and indicated lobsters in all groups had reached the same level of recovery 24 h post-treatment. Overall, the study demonstrated that lobsters recover rapidly from handling. Conversely, the increase in M ˙ O 2 induced by 2-phenoxyethanol demonstrated this is not an effective anaesthetic for reducing recovery periods and physiological stress associated with handling. However, 2-phenoxyethanol and clove oil eliminated further stress associated with force feeding, indicative of an invasive research procedure. Exercise to exhaustion resulted in the largest magnitude increase in M ˙ O 2 and longest recovery period. It is therefore recommended that aquaculture handling procedures take precautions to limit activity and are carried out without anaesthesia to facilitate more rapid recovery of lobsters.

Intraspecific analyses of the relationship between metabolic rate and mass have rarely been considered during complete ontogeny. Spiny lobsters are fascinating candidates to examine metabolic changes during ontogeny because their life cycle includes an extended planktonic, nektonic, and benthic life stages. The effect of body mass on metabolic rates, aerobic scope, and ammonia-N excretion of Sagmariasus verreauxi juveniles were examined to determine energetic demands through juvenile development. Mass-independent routine oxygen consumption increased allometrically during juvenile development with a mass scaling exponent of 0.83. The mass scaling exponent of active metabolism (0.81) was reduced compared to standard metabolism (0.91) of juvenile lobsters. The aerobic scope of juvenile lobsters decreased with larger body mass. To examine if the mass scaling exponent varies with ontogeny, we compared our data with previous measurements made with larvae of the same species. Comparison between mass scaling exponents showed they were higher for phyllosoma (0.97) compared to juvenile (0.83) development. Higher scaling exponents for phyllosoma may be attributed to increased growth rates of phyllosoma compared to juveniles, which increase oxygen consumption due to the higher energy cost of growth. The mass scaling exponent for complete ontogeny (0.91) of S. verreauxi was larger than the commonly cited 0.67 (1/3) and 0.75 (3/4) mass scaling exponents, indicating that species-specific differences can be a large factor affecting allometric relationships of animals.

Stocking density is a critical factor affecting performance of aquatic organisms in culture, however, its influence on energy utilisation has rarely been considered. Energy partitioning is particularly important for spiny lobster phyllosoma, which must accumulate sufficient energy reserves for metamorphosis and the non-feeding puerulus stage. The current study is the first to examine the energetics of spiny lobsters throughout the entire phyllosoma phase and determined the physiological influence of density. Growth and development, oxygen consumption and ammonia–N excretion rates were measured in Sagmariasus verreauxi phyllosoma that were cultured at High Density (HD) and Low Density (LD) from hatch to puerulus. Phyllosoma growth and development was more advanced in LD phyllosoma after 108 day in culture and mass of LD instar 17 phyllosoma was greater. There were no differences in routine metabolic rate ( R r ) and ammonia–N excretion of phyllosoma between densities. However, the O:N ratio decreased in final instar phyllosoma demonstrating a shift towards higher protein catabolism. Routine metabolic rate also increased in late stage phyllosoma, possibly due to higher energy requirements in preparation for metamorphosis and increased swimming activity. The R r of spiny lobster larvae was significantly lower than that of other crustacean larvae, which may be a characteristic of their extended larval phase, slower growth rate, and larger body size. The study demonstrated late stage phyllosoma have higher weight specific energy requirements than the preceding larval stages and exhibit a metabolic shift towards protein catabolism, suggesting an increased importance of storing lipid as an energy reserve for the puerulus stage.

Stocking density is an important factor affecting the competency of later stage lecithotrophic spiny lobster larvae, yet its influence on biochemical composition has rarely been considered. Biochemical analysis of phyllosoma during ontogeny provides information on the energy storage requirements of late instar phyllosoma and their ability to survive metamorphosis and achieve the energetic demands of the puerulus stage. The current study is the first to examine biochemical composition of spiny lobsters through the entire larval phase. Survival, growth, development, and biochemical composition were measured in Sagmariasus verreauxi phyllosoma that were cultured at High Density (HD) and Low Density (LD) from hatch to puerulus. Protein measured directly by Lowry was considerably lower than crude protein as calculated from nitrogen (N) content using N×6.25, suggesting that a conversion factor of 6.25 was too high. Survival of phyllosoma was significantly higher in the HD treatment after instar 9 due to high mortalities of LD phyllosoma caused by high ozonation during instar 9. However, HD phyllosoma were less susceptible to the high ozonation event possibly due to the larger biomass in HD tanks. Phyllosoma growth and development were more advanced in LD phyllosoma after 108 d. Instar 17 LD phyllosoma were also significantly larger than instar 17 HD phyllosoma. The C:N ratio confirmed proportionally more lipid than protein was accumulated during larval development before a significant decrease in lipid reserves between instar 17 and the puerulus stage by over 21% to fuel the process of metamorphosis and the non-feeding puerulus stage. The study demonstrated the larval phase of S. verreauxi is important for accumulating lipid reserves to fuel metamorphosis and the puerulus stage and provides a more complete picture of the culture requirements of spiny lobsters during ontogeny, particularly for the rarely studied late phyllosoma instars.

Mass propagation of spiny lobster phyllosoma is a critical bottleneck for the development of spiny lobster aquaculture. Eastern spiny lobster Sagmariasus verreauxi has been identified as a good candidate for temperate culture with a relatively short life cycle lasting 6 to 8 months and 17 stages. We investigated the development and functionality of the filter-press of S. verreauxi phyllosoma to better understand the size and quantity of dietary particles ingested over the entire larval cycle. Filter-press morphometrics were obtained from live phyllosoma larvae throughout development, and filtration capacity was ascertained using fluorescent microspheres and the rare earth metal markers yttrium oxide and ytterbium oxide. The filter-press of phyllosoma larvae was fully functional from stage 3, fully developed from stage 4, and the numbers (8 to 50), lengths (79 to 384 μm), and widths (14.8 to 20.3 μm) of food grooves increased with the development stage to accommodate a larger volume of ingested food. In contrast, there was no change in the widths of the lower ampullary setae (1.28 ± 0.16 μm) or the widths of the gap between these setae (0.91 ± 0.07 μm). Lower ampullary setae were arranged in a single layer perpendicular to the food grooves and restricted the entry of food particles into the digestive gland. From stage 3, the filter-press selectively excluded more than 99% of particles of > 1 μm from reaching the digestive gland and demonstrated that only particles of ≤ 1 μm are available for digestion. In the absence of a gastric mill, phyllosoma larvae have no obvious structure for internally grinding prey and the present study shows that phyllosoma larvae are well adapted to feed from the body fluids of wild preys over their entire larval cycle. The results have important practical applications for the development of formulated feeds for spiny lobster larvae.

n−3 Long-chain (≥ C 20 ) polyunsaturated fatty acids (LC-PUFA) are used extensively by fish via β-oxidation when in dietary surplus. Therefore it is of interest to optimize n−3 LC-PUFA deposition in fish via a reduction in β-oxidation which may be induced by manipulation of dietary fatty acids. This study tested whether Atlantic salmon smolt fed a diet with a higher docosahexaenoic acid (DHA):eicosapentaenoic acid (EPA) ratio and a lower content of n−3 LC-PUFA to that of fish oil (FO) based diets would enhance deposition of n−3 LC-PUFA in fish tissues. Comparisons were made between fish fed: a FO diet, a blend of 50% rapeseed and 50% tuna oil diet (model oil, MO 1), a blend of 50% rapeseed, 25% tuna and 25% FO diet (MO 2), and a blend of 50% FO and 50% chicken fat diet (FO/CF). The dietary DHA:EPA ratio was in the order MO 1 > MO 2 > FO/CF ~ FO. Dietary n−3 LC-PUFA content was approximately 2-fold lower in fish fed the MO 1, MO 2 and FO/CF diets compared to the FO diet. There were comparable amounts of n−3 LC-PUFA in the muscle of FO, MO 1 and FO/CF fed fish. Our findings indicate that the right balance in both absolute and relative amounts of EPA and DHA can promote n−3 LC-PUFA retention.

Southern bluefin tuna (Thunnus maccoyii) ranching in South Australia is one of the most valuable finfish aquaculture industries in Australia. This industry is currently highly reliant upon the use of baitfish; however commercial pelleted diets for this species are now available. Despite the economic importance of these animals there is a general lack of knowledge regarding the digestive physiology of southern bluefin tuna. Measurement of the digestive enzymes trypsin (T), chymotrypsin (C) and calculation of T:C ratios are particularly useful in the assessment of nutritional status in fish. In this study T and C activities were measured in ranched tuna fed a vitamin (Vit) and vitamin + immunostimulant (Vit + Imm) supplemented baitfish diet for 8 weeks. Differences relating to the addition of the supplements were not observed for T, C or T:C ratios suggesting that the supplementation rates did not affect the nutritional status of the tuna or the quality of the baitfish. Trypsin activity plays a key role in the secretion of chymotrypsin and in this study a significant correlation between these enzymes was found. T, C and T:C were not associated with caecum somatic index, caecum pH, caecum temperature, stomach pH or stomach temperature. Although T and C activities are highly sensitive to feeding, activities of these enzymes did not appear to be affected by the presence of baitfish in the stomach. The presence of baitfish did not appear to affect caecum pH, caecum temperature or stomach temperature. Therefore all data were pooled and a significant correlation between caecum and stomach temperature, explained by the endothermic physiology of tuna, was observed. Significantly higher stomach pH values were associated with the presence of baitfish and an inverse relationship between stomach pH and stomach temperature was found in fish with empty stomachs but not those that had eaten. These results are indicative of a digestive strategy which employs maintenance of low stomach pH for rapid digestion of a meal. This study represents the first report of digestive enzyme activities and nutritional status for captive southern bluefin tuna fed a standard and modified baitfish diet. In addition to a better understanding of digestive physiology, these results, in combination with the physiological measures of feeding and digestion, will significantly contribute to the further development of an in vitro digestive model for this species. This model will significantly improve the abilities of the Australian southern bluefin tuna industry to assess the predicted digestibility of commercially produced pelleted diets as well as screen novel dietary ingredients prior to full scale and often commercially expensive in vivo trials.

Vegetable oils (VO) are globally accepted alternatives for fish oil (FO) in aquafeeds. The lack of n-3 long-chain (≥ C 20 ) polyunsaturated fatty acids (n-3 LC-PUFA) in VO is a major constraint. Echium oil (EO), rich in stearidonic acid (SDA), has the potential to increase endogeneous n-3 LC-PUFA biosynthesis. We tested whether feeding Atlantic salmon an EO-based diet in both freshwater and seawater would increase n-3 LC-PUFA levels by comparing the fatty acid (FA) profiles in liver and white muscle to fish fed FO and rapeseed oil (RO)-based diets. The gene expression of n-3 LC-PUFA biosynthetic enzymes was measured to demonstrate the underlying mechanism of n-3 LC-PUFA biosynthesis. After prolonged feeding with EO diet from freshwater to seawater phases, EO fish had higher n-3 LC-PUFA levels in both liver and white muscle compared to RO fish. However, FO fish had the highest n-3 LC-PUFA levels in examined tissues. Δ6 Desaturase gene expression in liver and white muscle was up-regulated in RO fish only, liver Δ5 desaturase gene expression was reduced in seawater and liver FA elongase gene expression was regulated by an interaction between dietary oil and environment. This study showed that feeding Atlantic salmon from parr to smolt using an SDA enriched diet increases n-3 LC-PUFA biosynthesis in liver and white muscle through increased supply of the n-3 LC-PUFA precursor SDA. The down regulation of Δ5 desaturase gene expression in the liver of seawater fish may explain environmental differences in n-3 LC-PUFA biosynthesis.

Although protein metabolism has been studied in fish and other crustaceans, this is the first study to measure protein synthesis rates for Norway lobster Nephrops norvegicus. This research aimed to assess the nutritional status of wild caught Nephrops by measuring tissue rates of protein synthesis and comparing these with rates from fed and starved Nephrops maintained in aquaria. Rates of protein synthesis were measured in the hepatopancreas, gill and tail muscle tissue. A time-course validated the use of a flooding-dose of 3 H phenylalanine to measure protein synthesis in Nephrops and showed that the flooding-dose method is suitable for the study of protein turnover in Nephrops. The relationship between the measured rate of protein synthesis and capacity for protein synthesis (Cs) showed differences between tissues and between nutritional history. Measures of protein metabolism were generally higher in hepatopancreas, then gill and then tail muscle and generally lower in starved animals. Although individual variation meant there were few significant differences in tail muscle values between treatments, RNA concentration was higher in wild-caught than starved and suggested they were not starving. This was supported by hepatopancreas protein synthesis in wild-caught being intermediate between fed and starved, indicating relatively recent feeding had increased hepatopancreas protein synthesis due to increased RNA activity at constant RNA capacity. This study will add to our current but limited understanding of the effects of environmental variations on nutritional status and on protein metabolism and deposition in Nephrops species. Knowledge of the mechanisms enabling their survival is required to understand their ability to adapt to environmental variables.

For aquatic ectotherms, increasing water temperatures cause an exponential increase in metabolic rate and decreasing oxygen solubility. Fish species that regulate their metabolic rate to low dissolved oxygen concentrations are understood to be hypoxia tolerant whereas salmonid fish are considered to be classic metabolic conformers and their metabolic rate is dependent on the environmental oxygen concentration. This study examined Atlantic salmon, Salmo salar , undergoing a progressive hypoxia at optimal temperatures and at temperatures nearing the upper thermal tolerance limit for the species to determine if metabolic regulation occurred. Oxygen consumption was measured on individual Atlantic salmon (150.7 ± 40.8 g) in 66-L static respirometers; oxygen measurements were taken every 5 min until the fish lost equilibrium. Metabolic regulation was observed at all temperatures and occurred in 67, 50 and 50% of the fish at 14, 18 and 22 °C, respectively. The plateau metabolic rate (VO 2PL ) was 293.4 ± 24.5 mg·kg·h − 1 at 22 °C which was significantly higher than in the 14 and 18 °C treatments (191.1 ± 24.5 and 203.9 ± 12.6 mg·kg·h − 1 , respectively). This difference was also reflected in the critical oxygen threshold (P crit ) where the value for the 22 °C treatment (4.59 ± 0.32 mg·L − 1 ) was significantly higher than those of the 14 and 18 °C treatments (3.46 ± 0.14 and 3.39 ± 0.26 mg·L − 1 respectively). These results indicate that some fish from the Tasmanian population of Atlantic salmon have the ability to regulate metabolic rate to low oxygen concentrations and therefore show a relatively high degree of hypoxia tolerance.

This study investigated the efficiency of lysine utilisation for liveweight gain (LG), protein gain (PG) and lysine gain (LysG) in Atlantic salmon (Salmo salar L.) parr fed a diet with a high digestible protein (DP) to digestible energy (DE) ratio. Twelve diets containing 10.15 to 20.79 g dietary digestible lysine (DDLys) kg−1 at a constant 25.0 g DPMJ DE−1 (25.0 DP DE−1) were fed at a fixed ration for 50 days. With increasing DDLys there was a significant (Pb0.001) linear increase in LG. Whole-body crude protein and lysine content increased with increasing wet weight (W), with weight exponents b (Wb) of 1.58 and 2.47, respectively. There were significant linear relationships between digestible lysine intake (DLysI) and LG, PG and LysG. The relationship between DLysI and LysG predicted a maintenance lysine requirement of 7.7 mg kg−0.75 d−1 and an efficiency of 77% for lysine utilisation for lysine gain above maintenance lysine intake. To further examine the effect of the DP DE ratio on lysine utilisation comparison was made to a similar study that used a lower DP DE ratio of 19.8 DP DE−1. Comparison between linear relationships for LG, PG and LysG from the two experiments showed that there were no significant differences between the efficiency of lysine utilisation (slopes) for LG, PG or LysG, nor were there significant differences between the elevations for PG and LysG. This study demonstrated that at two fixed but different protein and energy intakes the dietary DP DE ratio did not influence the efficiency of lysine utilisation for lysine gain over a range of dietary lysine and digestible lysine intakes.

Vegetable oils (VO) are sustainable sources for replacement of fish oil (FO) in aquafeeds. However, VO lacks the health-benefitting n-3 long-chain (－ C20) polyunsaturated fatty acids (n-3 LC-PUFA) and potentially compromise farmed fish flesh quality for consumers. In a factorial experiment, barramundi (Lates calcarifer) were grown in either freshwater or seawater and fed on three diets containing different oil sources: FO; stearidonic acid (SDA, 18:4n-3) rich oil from Echium plantagineum (EO); or rapeseed oil (RO). RO and FO-fed fish grew faster than the EO treatment and all three dietary treatments were not affected by salinity. A fatty acid mass balance showed that feeding barramundi on EO diet bypassed the first rate-limiting step in n-3 LC-PUFA biosynthesis. However, the fish did not accumulate high EPA or DHA content. Total PUFA, mainly of the n-3 series and dominated by ALA (18:3n-3) and SDA, in the whole body of EO fish was higher than for the FO and RO treatments. The n-3:n-6 ratio in EO treatment was less than for FO, but exceeded that in RO-fed fish. FA apparent metabolism as derived from the fatty acid mass balance fluxes showed comparable kinetics for key enzymes, indicating limited efficiency for LC-PUFA biosynthesis from their C18 dietary precursors in barramundi fed EO or RO containing diets. Fish digested dietary FA and accumulated them efficiently regardless of the salinity. These findings establish a more comprehensive understanding for FA metabolism in barramundi fed different dietary lipids and at extremes of the species wide salinity range. Based on the observed levels of accumulation, EO-fed barramundi are a potentially rich source of ALA and SDA for human consumption. Keywords: Lates calcarifer; Oil replacement; Fatty acid metabolism; Stearidonic acid

An experiment was conducted to evaluate the interactive effects of dietary palm fatty acid distillate (PFAD) and water temperature on lipid and fatty acid digestibility in rainbow trout. Three isolipidic diets with 0, 10 or 15% (w/w) PFAD, at the expense of fish oil, were formulated and fed to triplicate groups of trout maintained at water temperatures of 15 or 20 °C. The apparent digestibility (AD) of fatty acids was measured using yttrium oxide as an inert marker. Increasing dietary PFAD, which contains mainly free fatty acids (FFA), led to a significant (Pb0.05) improvement in the AD of saturated fatty acids (SFA) but not that of total monounsaturated or polyunsaturated fatty acids in trout maintained at both water temperatures. High AD of total lipids (90–93%) was observed in all treatments. Based on fecal lipid class and fatty acid composition, this improvement in SFA digestibility was due in part to the increased absorption of the FFA as it bypasses the need for lipolysis. Elevated water temperature tended to cause a reduction in the AD of most fatty acids at each corresponding dietary treatment. The AD of individual fatty acids within each water temperature regimen generally decreased with increasing fatty acid chain length and increased with increasing unsaturation, irrespective of diet. In general, no significant interaction between diet and temperature effects on fatty acid digestibility was found. © 2010 Elsevier B.V. All rights reserved

The experiment aimed to measure post-prandial protein synthesis at three different temperatures. Juvenile barramundi (10.81+/-3.46 g) were held at 21, 27 and 33 degrees C and fed to satiation daily. Samples were taken over a 24h period at 0 (24h after the previous meal) and then at 4, 8, 12 and 24h after feeding to measure protein synthesis in the white muscle, liver and remaining carcass. Protein synthesis at 27 and 33 degrees C peaked 4h after feeding in all tissues and returned to pre-feeding rates by 12h. At 21 degrees C protein synthesis remained constant over 24h in all tissues. While the concentration of RNA remained stable over the 24h cycle and across temperatures, the ribosomal activity increased after feeding. This meant k(RNA), not the absolute amount of RNA, was the driving force underlying the post-prandial increase in protein synthesis. However, relative differences in protein synthesis between tissues were attributed to differences in RNA concentration. There was a significant positive relationship between white muscle and whole body protein synthesis. This was the first study to show an interaction between temperature and the time after feeding on protein synthesis for an ectotherm, and that a post-prandial peak in protein synthesis only occurred under optimum temperature conditions.

The striped trumpeter ( Latris lineata ) is a promising new candidate for diversification of aquaculture in temperate regions of Australasia. Striped trumpeter is also of scientific interest due to an unusually prolonged post-larval phase. The research aimed to identify the optimal temperature for rearing post-larval striped trumpeter approaching metamorphosis. Three-hundred-day-old post-hatch post-larvae (12.1 ± 0.2 g, 114.0 ± 0.5 mm, mean ± SE) were reared at 12, 14, 16 and 18 °C, over 84 days. Survival, growth and metamorphosis into juveniles were recorded every 21 days. Fish were fed to apparent satiation and reared in oxygen saturated water (95.9 ± 2.6%). At 14 °C, fish exhibited the best growth, had significantly higher lipid content and the majority (> 90%) of the population metamorphosed into juveniles. The performance of fish reared at 16 °C was similar to those at 14 °C but the carcass had a significantly higher protein content and a significantly smaller proportion of the population (66.2 ± 3.0%) metamorphosed into juveniles. A specific growth rate model showed that growth was highest at 14.4 °C. At 12 °C, fish showed the highest food conversion efficiency and all of the fish metamorphosed into juveniles. At 18 °C, fish showed the lowest growth, metamorphosis, and protein and energy retention. This is the first study on the effects of temperature on growth and development of striped trumpeter post-larvae. The results have important implications for aquaculture and fisheries management of striped trumpeter, in particular the rearing of post-larvae in hatcheries, timing of stocking into sea cages especially prior to metamorphosis, and for wild stock recruitment models.

Experimental lobster feeds are currently based on fish meal and fish oil formulations, and although survival and growth similar to that of lobsters fed fresh blue mussels has been achieved, varying the protein level in previous experimental feeds has not increased growth beyond that of lobsters fed natural food. This experiment assessed the growth performance of lobsters fed pelleted feeds containing constant amounts of protein, lipid and energy where the lipid was provided by a range of oil-rich ingredients (fish oil, FO; fish oil with added soybean lecithin, FOL; canola oil, CO; tuna oil, TO; mussel meal, MM; and squid meal, SQM). Feed performance was assessed by lobster growth rate, survival, final biochemical composition, nutrient retention and nutrient efficiency. Twenty tanks containing 15 post-larval lobsters each (1.5 ± 0.04 g) were randomly allocated one of six test feeds in triplicate, and the two remaining tanks were fed freshly opened blue mussels (FRM) as a reference feed. Lobsters were fed daily to excess for 10 weeks. Final individual weights of whole body and digestive gland were measured, and tissue chemical composition analysed. There were no significant differences in survival (88.4 ± 3.3%), or specific growth rate (1.3 ± 0.1%.day − 1 ) among the formulated feed fed lobsters, which were significantly lower than the survival (100 ± 0.0%) and SGR (2.2 ± 0.1%.day − 1 ) of FRM fed lobsters. The SQM fed lobsters had a significantly lower lipid efficiency ratio and lipid productivity value than lobsters fed TO, FOL and MM feeds. The digestive gland lipid content (g.100 g wet tissue − 1 ) of lobsters fed the feeds TO (3.7 ± 0.4), FO (3.5 ± 0.3) and SQM (2.2 ± 0.2) were significantly lower than lobsters fed feeds MM (9.9 ± 1.1), FOL (9.0 ± 2.3) and FRM fed lobsters contained most digestive gland lipid (12.3 ± 1.5).

Purpose The primary aim of our study was to investigate use of long axis computed tomography (CT) in predicting avascular necrosis of the proximal pole of the scaphoid and subsequent fracture nonunion after internal fixation. In addition, we describe a new technique of measuring the position of a scaphoid fracture and provide data on its reproducibility. Methods Thirty-one patients operated on by the senior author for delayed union or nonunion of scaphoid fracture were included. Preoperative CT scans were independently assessed for increased radiodensity of the proximal pole, converging trabeculae, degree of deformity, comminution, and fracture position. Intraoperative biopsies of the proximal pole were obtained and histologically assessed for evidence of avascular necrosis. The radiologic variables were statistically compared with the histologic findings. The presence of avascular necrosis was also compared with postoperative union status, identified on longitudinal CT scans. Results Preoperative CT features that statistically correlated with histologic evidence of avascular necrosis were increased radiodensity of the proximal pole and the absence of any converging trabeculae between the fracture fragments. The radiologic changes of avascular necrosis and the histologic confirmation of avascular necrosis were associated with persistent nonunion. Conclusions Preoperative longitudinal CT of scaphoid nonunion is of great value in identifying avascular necrosis and predicting subsequent fracture union. If avascular necrosis is suspected based on preoperative CT, management options include vascularized bone grafts and bone morphogenic protein for younger patients and limited wrist arthrodesis for older patients. Type of study/level of evidence Diagnostic II.

Rates of protein synthesis were measured in the whole body and tissues of southern dumpling squid Euprymna tasmanica to validate the use of a flooding-dose of (3)H phenylalanine for the measurement of protein synthesis with different size squid and to make a preliminary investigation into the effects of feeding regime. In smaller (2.8+/-0.5 g, mean+/-SE) and larger (14.8+/-2.2 g) squid whole body fractional rates of protein synthesis were 9.45+/-1.21 and 1.49+/-0.29% d(-1), respectively. Differences in total whole body protein content meant there was no difference in absolute rates of whole body protein synthesis between the larger and smaller squid. In larger squid, fractional rates of protein synthesis were significantly higher in the digestive gland (9.24+/-1.63% d(-1)) than in the arm tissue (1.43+/-0.31% d(-1)), which were significantly higher than in the anterior (0.56+/-0.13% d(-1)) and posterior (0.36+/-0.04% d(-1)) mantle. In smaller squid there were no differences in protein synthesis between tissues and high individual variation, due to differences in feeding, was a likely cause. Consequently, the effect of feeding regime on protein synthesis was compared between two groups of individually held squid: daily-feeding and minimal-feeding squid. The daily-feeding squid had significantly higher feed intake, gained mass and had a significantly higher growth rate than the minimal-feeding squid which lost mass. Whole body protein synthesis was significantly higher in the daily-feeding squid as was the protein content of the digestive gland, anterior and posterior mantle. There were few other differences in indices of protein metabolism. Individual squid showed differences in growth and protein metabolism, and there were significant relationships between growth rate and both rates of protein synthesis and protein degradation. Thus, higher individual growth was a consequence of increased protein synthesis, decreased protein degradation and, therefore, increased efficiency of retaining synthesised protein.

Atlantic salmon (Salmo salar L.) can produce (n-3) long-chain (LC)-PUFA when fed biosynthetic precursors. This has potential for developing sustainable aquafeeds. Echium oil (EO) is rich in stearidonic acid [SDA; 18:4(n-3)] and bypasses the initial D6 desaturase (FAD6) step in the (n-3) LC-PUFA biosynthetic pathway. EO was fed to seawater Atlantic salmon for 12 wk and compared with fish fed a diet containing canola oil (CO), a source of a-linolenic acid [ALA; 18:3(n-3)] or fish oil (FO) that provides (n-3) LC-PUFA. Fatty acid (FA) composition of liver, white muscle, and whole fish was measured to show whether dietary precursors were endogenously biosynthesized to LC-PUFA. Gene expression of liver FA elongase and FAD5 was upregulated in EO fish compared with FO fish. Furthermore, dietary precursors affected the FA concentrations of direct biosynthetic products in all tissues. The increased gene expression in the EO fish was reflected by an increased FA concentration of eicosapentaenoic acid [20:5(n-3)] in the liver compared with the CO fish. However, the high concentrations of (n-3) LC-PUFA found in seawater Atlantic salmon fed diets rich in FO were not attained via biosynthesis from precursors (ALA or SDA) in diets.

This study investigated whether the efficiency of lysine utilisation for liveweight gain, protein gain and lysine gain was affected by feeding regime in Atlantic salmon (Salmo salar L.) parr. Twelve diets containing from 10.15 to 20.79 g dietary digestible lysine kg− 1 were hand-fed either to satiation or to a controlled fixed ration. The controlled ration was set to equal the feed intake of the basal (lowest) lysine diet so that any growth above that of the group fed the basal diet at the controlled ration was due entirely to the additional dietary lysine. For both feeding regimes, with increasing dietary lysine there were significant linear increases in liveweight gain (P < 0.001) and in protein (P < 0.001) and lysine (P < 0.01) concentration of liveweight gain. Increasing dietary lysine resulted in a significant (P < 0.001) linear increase in feed intake at satiation. Efficiency of lysine utilisation for liveweight gain above maintenance lysine intake was significantly (P < 0.005) higher at satiation than for the controlled ration: 47.7 compared to 34.9 mg liveweight gain per mg digestible lysine intake, respectively. However, feeding regime had no significant effect on the efficiency of lysine utilisation for protein or lysine gain. This study demonstrated that feed intake does not influence the efficiency of lysine utilisation for protein or lysine gain in Atlantic salmon parr. The change in weight-specific lysine composition suggests a robust physiological mechanism maintaining the efficiency of lysine utilisation for lysine gain in Atlantic salmon parr.

Temperature has a marked and direct effect on many of the key physiological processes in ectotherms, including fish. Results from two growth trials on juvenile barramundi (∼ 3–5 g) were used to model the effects of temperature on the feed intake and growth performance, measured as specific growth rate (SGR), productive protein value (PPV) and productive energy value (PEV), across temperatures 21–39 °C (at 3 °C intervals). There were no significant differences between the chemical composition of the fish reared at different temperatures. Optimal temperatures were determined from quadratic polynomials: maximum feed intake (g d − 1 ), maximum growth (SGR, % d − 1 ) and growth efficiency (PPV and PEV, %) occurred at 32.8, 31.4, 31.2 and 30.2 °C, respectively. These models also determined that maximum growth occurred approximately 4 °C higher then previously demonstrated. Feed intake, SGR and growth efficiency remained ≥ 90% of the maximum biological response over an 8 °C temperature range. These models suggest that juvenile barramundi are eurythermal and therefore maximize growth by adopting strategies to optimize nutrient utilization over as wide a temperature range as possible. Furthermore, the decrease in growth efficiency at extreme (high) temperature occurs over only a few degrees and highlights the upper thermal tolerance of barramundi.

Temperature is recognized to be the most important environmental factor affecting growth and protein synthesis in fish. The optimal temperature for growth of juvenile barramundi is 31 °C, although culture often occurs at temperatures which are above and below this optimum. Juveniles (2.96 ± 0.46 g) were held at five different temperatures ranging from 21 to 33 °C at 3 °C intervals. Fish were fed to satiation twice daily (504.5 g kg− 1 crude protein, 190.5 g kg− 1 lipid, 128.5 g kg− 1 ash, and 20.2 GE MJ kg− 1). Daily feed intake (g), growth (% d− 1), growth efficiency, and protein synthesis (measured 24 h after feeding) were determined for each temperature. Feed intake was significantly higher at 33 °C, than at any other temperature. Growth and growth efficiency were not significantly different between the 27, 30 and 33 °C groups but were significantly higher than the 21 and 24 °C groups. In order to take account of the variation in protein synthesis over the 24 h following feeding and model daily protein turnover, daily rates of protein synthesis were estimated from previously determined relationships between white muscle and whole body rates of protein synthesis. This showed that protein synthesis was not significantly different between 27 and 33 °C, synthesis retention efficiency was over 40% at these temperatures, and at 21 °C growth efficiency was poor. Growth efficiency and protein metabolism were optimal over a temperature from 27 to 33 °C.

The worldwide increase in aquaculture production and the concurrent decrease of wild fish stocks has made the replacement of fish oil in aquafeeds an industry priority. Oil from a plant source Echium plantagineum L., Boraginaceae, has high levels of stearidonic acid (SDA, 18:4omega3, 14%) a biosynthetic precursor of omega-3 long-chain (or =C(20)) polyunsaturated fatty acids (omega3 LC-PUFA). Atlantic salmon (Salmo salar L.) parr were fed a control fish oil diet (FO) or one of 3 experimental diets with 100% canola oil (CO) 100% SDA oil (SO), and a 1:1 mix of CO and SDA oil (MX) for 42 days. There were no differences in the growth or feed efficiency between the four diets. However, there were significant differences in the fatty acid (FA) profiles of the red and white muscle tissues. Significantly higher amounts of SDA, eicosapentaenoic acid (20:5omega3, EPA), docosahexaenoic acid (22:6omega3, DHA) and total omega3 FA occurred in both red and white muscle tissues of fish fed SO and FO compared with those fed CO. Feeding SO diet resulted in omega3 LC-PUFA amounts in the white and red muscle being comparable to the FO diet. This study shows that absolute concentration (mug/g) of EPA, DHA and total omega3 have been maintained over 6 weeks for Atlantic salmon fed 14% SDA oil. The balance between increased biosynthesis and retention of omega3 LC-PUFA to maintain the concentrations observed in the SO fed fish remains to be conclusively determined, and further studies are needed to ascertain this.

This study aimed to compare nitrogen budgets for juvenile (1.17 ± 0.07 g, mean ± S.D.) big-bellied seahorses fed live, frozen and pelleted feeds and to examine the potential of non-destructive measurements of excretion to predict feed performance. Three feeds were tested against live Artemia: frozen mysid shrimp species (Paramesopodopsis rufa, Tasmanomysis oculata,Tenagomysis sp.), a pellet prepared from the mysid shrimps and a commercial crumbled feed. Nitrogen budgets were constructed from nitrogen retention measured over a 30 day growth experiment, ammonia and urea excretion measured over 24 h on days 15 and 30, and nitrogen digestibility. After 30 days seahorses fed Artemia and frozen mysid had significantly (P

Temperature is recognized to be the most important environmental factor affecting growth in fish. Barramundi are cultured over a wide range of temperatures and extreme high temperatures which they can experience under culture approach the upper thermal tolerance limit for this species. A growth trial was conducted on juvenile barramundi to examine the effects of high temperatures ranging from the minimum optimal temperature (27 degrees C) for growth efficiency to the extreme upper thermal limits (39 degrees C) for feed intake, growth and growth efficiency. Juveniles (4.87 plus or minus 0.32 g) were held at four different temperatures 27, 33, 36 and 39 degrees C and fed twice daily to satiation (503.5 g kg-1 crude protein, 182.5 g kg-1 lipid, 150.1 g kg-1 ash, 20.52 GE MJ kg-1). Feed intake (g per day) and SGR (% per day) increased with increasing temperature up to 36 degrees C. At 39 degrees C feed intake, growth, feed efficiency ratio, protein efficiency ratio and productive energy value were significantly lower than at the other temperatures. This demonstrates that growth was optimized at temperatures from 27 to 36 degrees C and that barramundi have a much wider range for maximum growth efficiency than preciously thought.