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Cardiac abnormalities may pose a threat to salmonid aquaculture due to their potential detrimental effect on fish health and welfare. The teleost heart is an extremely plastic organ with important morphological differences between wild and farmed fish that include ventricular shape, alignment of the bulbus arteriosus and epicardial fat deposition. However, little is known about how different factors and interactions among them may affect cardiac morphology of Atlantic salmon. To determine whether rearing temperature could induce cardiac malformations in large Tasmanian Atlantic salmon, we examined a range of cardiac morphology indicators and growth parameters in a population of 1-2 kg seawater salmon (n = 60 temperature-1 diet-1 ) exposed to control and elevated temperatures of 15 and 19°C, respectively, while fed one of two commercial feeds with different dietary energy levels. Most fish possessed conspicuous fat around the heart with a tendency towards a rounded ventricle and a more obtuse angle of the bulbus arteriosus. However, fish showed no significant differences in heart shape and bulbus alignment in relation to water temperature and dietary energy. These results suggest that cardiac morphology of large Atlantic salmon is unlikely to be affected by rearing temperature and dietary energy during the grow-out phase.

Chinook salmon (Oncorhynchus tshawytscha), also referred to as King salmon, is a premium aquaculture species farmed in New Zealand and to a small extent in western Canada. Despite the high research investment in the 50s and 60s, literature on nutrition on chinook salmon from recent years is sparse, particularly when compared to other salmonid aquaculture species, such as Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). To improve fish productivity, it is essential to provide specific and efficient diets based on satisfying chinook salmon requirements for nutrients and energy and adapting these to life-stage, season, and production variables. Diet specifications for chinook salmon have to date largely been based on knowledge derived from other salmonid species and may not be optimised for chinook salmon. Thus, there is a lack of knowledge in some fundamental areas. This review explores the production status and literature related to the macro and micronutrient requirements, and general nutrition of chinook salmon. In doing so it compares these requirements to other farmed salmonids to understand some of the differences between species and highlights the main gaps in the literature.

The respiratory quotient (RQ) has been used extensively as an index to evaluate metabolic energy expenditure in terrestrial animals including humans. In contrast, RQ use in understanding physiology and nutrition of aquatic ectotherms has been restricted due to technical challenges in measuring total CO2 in water. With technical advances in measuring total CO2 in water, RQ in aquatic ectotherms can be accurately determined and is potentially available as a valuable method. Here, we provide a comprehensive review of studies on RQ and metabolic energy substrate use in aquatic ectotherms. Metabolic energy substrate use is evaluated by a reliable stoichiometric bioenergetic approach, based on measuring RQ and nitrogen quotient (NQ) simultaneously. Stoichiometry provides a non‐destructive and unequivocal way to quantify the instantaneous oxidation of each major energy substrate (protein, lipid or carbohydrate). This review aims to refine knowledge about bioenergetics of aquatic ectotherms under different conditions including nutritional aspects of sustainable aquaculture. Notably, stoichiometry provides a promising approach to optimize feeds and feeding regimes to realize sustainable aquaculture under differing conditions and with differing feed ingredients. It also provides an approach to consider climate change impacts and physiological adaptation mechanisms for survival and development in farmed environments and natural ecosystems. Stoichiometric bioenergetics knowledge in aquatic ectotherms has relevance to commercial impacts in the face of overfishing and food security, and ecological significance in the face of environmental change scenarios. We suggest expanding the use of stoichiometry in future bioenergetic research in emerging aquaculture species.

Aquaculture is critical for ensuring global food and nutrition security, and fed-aquaculture, which depends on formulated nutritionally balanced manufactured feeds, must be sustainable. Single-cell ingredients (SCI) are predicted to play a significant role in future aquafeeds and have the potential to underpin sustainable fed-aquaculture for many species. The value of an aquafeed ingredient includes nutritional, commercial, environmental, and socioeconomic factors. Here we aim to review approaches to understanding the value of ingredients and use this to outline a practical approach for considering the use of SCI in aquafeeds. We conclude that following an initial experimental focus on nutritional value, a collaborative and iterative approach with an aquafeed manufacturer will provide the most likely route to successful commercialisation of SCI.

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).

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.

Simple Summary Using combinations of plant protein concentrates and EAA supplementation, high levels of replacement (50–75% of fishmeal protein) have been achieved in gilthead sea bream without affecting the growth performance or quality traits. It was confirmed in this study that 16% replacement of marine protein with plant protein meets the amino acid needs of sea bream. The results of the present study suggest the need to further investigate tissue-specific and species-specific responses in the timing and ability to regulate metabolism due to dietary nutrient utilization. Abstract Following a meal, a series of physiological changes occurs in fish as they digest, absorb and assimilate ingested nutrients. This study aims to assess post-prandial free amino acid (FAA) activity in gilthead sea bream consuming a partial marine protein (fishmeal) replacement. Sea bream were fed diets where 16 and 27% of the fishmeal protein was replaced by plant protein. The essential amino acid (EAA) composition of the white muscle, liver and gut of sea bream was strongly correlated with the EAA composition of the 16% protein replacement diet compared to the 27% protein replacement diet. The mean FAA concentration in the white muscle and liver changed at 4 to 8 h after a meal and was not different to pre-feeding (0 h) and at 24 h after feeding. It was confirmed in this study that 16% replacement of marine protein with plant protein meets the amino acid needs of sea bream. Overall, the present study contributes towards understanding post-prandial amino acid profiles during uptake, tissue assimilation and immediate metabolic processing of amino acids in sea bream consuming a partial marine protein replacement. This study suggests the need to further investigate the magnitude of the post-prandial tissue-specific amino acid activity in relation to species-specific abilities to regulate metabolism due to dietary nutrient utilization.

Marine tropical carnivorous (MTC) fish are less tolerant to high dietary lipid compared with cold and temperate climate fish. However, insufficient n‐3 long‐chain (≥C 20 ) polyunsaturated fatty acids (LC‐PUFA) compromises MTC fish health and growth which requires attention when choosing lipid sources in aquafeed formulations. Fish oil (FO) has been the major lipid source for feeding key MTC fish. We estimated that more than 200 thousand tonnes of FO were used to feed farmed MTC fish in 2016, representing nearly 25% of global FO production. Nevertheless, recent increases in FO prices and demand, and the foreseen inability of wild fisheries to produce sufficient FO in the future, have created a need for cheaper and more sustainable alternatives. Meta‐analysis showed that feeding vegetable oils (VO) to MTC fish can slightly reduce their growth, with a marked decrease in n‐3 LC‐PUFA content in the fish tissues corresponding with the increased replacement of FO and fishmeal in the diet. Rendered terrestrial animal fat or modulating the bioconversion of n‐3 LC‐PUFA precursors in VO can be utilised further in MTC fish nutrition with more research recommended on these approaches. Oils and oil‐rich meals from non‐food marine organisms are rich in n‐3 LC‐PUFA and represent an underutilised alternative to FO for tropical aquaculture. With oils rich in n‐3 LC‐PUFA produced from transgenic plants presently gaining regulatory approvals and becoming available as a renewable alternative to FO, aquaculture in the tropics and around the globe is ready to leap into a new phase of sustainable expansion.

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.

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.

Triploid Atlantic salmon populations are associated with higher prevalence of lower jaw skeletal anomalies affecting fish performance, welfare and value deleteriously. Anomalous lower jaw can be curved downward (LJD), shortened (SJ) or misaligned (MA). Two separate groups of triploid Atlantic salmon (~12 g) with either normal lower jaw (NOR) or SJ were visually assessed four times over three months for presence and concurrence of jaw anomalies (with severity classified) and opercular shortening to understand the relatedness of these anomalous developmental processes. The prevalence of jaw anomalies increased in both groups over time (NOR group - SJ, LJD and MA combined 0-24.5%; SJ group - LJD and MA combined 17-31%). SJ and LJD occurred both independently and concurrently whereas MA exclusively concurred with them. All three anomalies could be concurrent. Severity of both LJD and SJ increased in the SJ group only. Opercular shortening recovery was observed in both groups but at a slower rate in the SJ group. The SJ group specific growth rate (SGR) was significantly (P

Triploid Atlantic salmon tend to develop a higher prevalence of skeletal anomalies. This tendency may be exacerbated by an inadequate rearing temperature. Early juvenile all-female diploid and triploid Atlantic salmon were screened for skeletal anomalies in consecutive experiments to include two size ranges: the first tested the effect of ploidy (0.2–8 g) and the second the effect of ploidy, temperature (14 °C and 18 °C) and their interaction (8–60 g). The first experiment showed that ploidy had no effect on skeletal anomaly prevalence. A high prevalence of opercular shortening was observed (average prevalence in both ploidies 85.8%) and short lower jaws were common (highest prevalence observed 11.3%). In the second experiment, ploidy, but not temperature, affected the prevalence of short lower jaw (diploids > triploids) and lower jaw deformity (triploids > diploids, highest prevalence observed 11.1% triploids and 2.7% diploids) with a trend indicating a possible developmental link between the two jaw anomalies in triploids. A radiological assessment (n = 240 individuals) showed that at both temperatures triploids had a significantly (P

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.

The nutritional condition of cultured Sagmariasus verreauxi juveniles over the molt and during starvation was investigated by studying their metabolism, bioenergetics of nutrient reserves, and hemolymph biochemistry. Juveniles were shown to downregulate standard metabolic rate by as much as 52% within 14 d during starvation. Hepatopancreas (HP) lipid was prioritized as a source of energy, but this reserve represented only between 1% and 13% of the total measured energy reserve and was used quickly during starvation, especially in the immediate postmolt period when as much as 60% was depleted within 3 d. Abdominal muscle (AM) protein represented between 74% and 90% of the total measured energy reserve in juvenile lobsters, and as much as 40% of available AM protein energy was used over 28 d of starvation after the molt. Carbohydrate reserves represented less than 2% of the measured total energy reserve in fed intermolt lobsters and provided negligible energy during starvation. Eighteen hemolymph parameters were measured to identify a nondestructive biomarker of condition that would reflect accurately the state of energy reserves of the lobster. Among these, the hemolymph Brix index was the most accurate and practical method to predict HP lipid and the total energy content of both the HP and the AM in juvenile S. verreauxi. The Brix index was strongly correlated with hemolymph proteins, triglyceride, cholesterol, calcium, and phosphorus concentrations, as well as lipase activity; all were useful in predicting condition. Electrolytes such as chloride, magnesium, and potassium and metabolites such as glucose and lactate were poor indicators of nutritional condition. Uric acid and the "albumin"-to-"globulin" ratio provided complementary information to the Brix index, which may assist in determining nutritional condition of wild juvenile lobsters of unknown intermolt development. This study will greatly assist future ecological studies examining the nutritional condition of juvenile lobsters in the wild, as well as the development of husbandry protocols and feeds for aquaculture.

The digestible protein (DP) and digestible energy (DE) requirements for maintenance and growth of brook trout (Salvelinus fontinalis) were determined using a factorial model at either optimum (15 °C) or elevated temperature (19 °C). Several key parameters of the factorial model were measured using a series of inter-related studies. The maintenance requirements for DP and DE were 0.10 gDP kg−0.69 day−1 (15 °C) and 0.31 gDP kg−0.78 day−1 (19 °C), and 34.86 kJDE kg−0.84 day−1 (15 °C) and 46.14 kJDE kg−0.86 day−1 (19 °C). The total requirements for DP were 0.10 gDP kg−0.69 day−1 + 2.14PG (protein gain) (15 °C) and 0.31 gDP kg−0.78 day−1 + 1.98PG (19 °C). The total requirements for DE were 36.86 kJDE kg−0.84 day−1 + 1.58EG (energy gain) (15 °C) and 46.14 kJDE kg−0.86 day−1 + 1.64EG (19 °C). The partial efficiencies for growth were 0.47 (15 °C) and 0.51 (19 °C) for protein, and 0.63 (15 °C) and 0.61 (19 °C) for energy. Nutrient gain was lower at the elevated temperature; however, feed formulation for brook trout should be adjusted to match changes in nutrient requirements at different culture temperatures. The protein and energy requirements model will be useful for developing commercial feeds and feeding charts for brook trout.

Understanding how aquatic species respond to extremes of DO and temperature is crucial for determining how they will be affected by climate change, which is predicted to increasingly expose them to levels beyond their optima. In this study we used novel animal-borne DO, temperature and depth sensors to determine the effect of extremes of DO and temperature on the vertical habitat use of Atlantic salmon Salmo salar in aquaculture cages. Salmon showed a preference for temperatures around 16.5 to 17.5 °C, however, selection of preferred temperatures was trumped by active avoidance of low DO (20.1 °C), which led to a considerable contraction in the available vertical habitat. Despite their avoidance behavior, fish spent a large amount of time in waters with suboptimal DO (

The Southern rock lobster, Jasus edwardsii, is a temperate species of spiny lobster with established well managed fisheries in Australia and New Zealand. It has also been under consideration as a species with aquaculture potential. Agonistic behaviour has important consequences under aquaculture conditions that encompass direct effects, such as damage or death of protagonists, and indirect effects on growth that relate to resource access, principally food and refuge. This study aimed to identify and characterize behaviours and to make a preliminary investigation of their occurrence under tank culture. Juvenile Jasus edwardsii were examined in a flow-through seawater system using a remote video camera system. Twenty-nine behaviours were divided into three sub-groups: aggressive (11), avoidance (6) and others (12). Aggressive behaviours included attacks, pushing, lifting, clasping and carrying an opponent. Avoidance behaviours included moving away in a backwards-, forwards- or side-stepping motion as well as with more vigorous tail flips. These behaviours were components of twelve behavioural groups that described contact, attack and displacement between individuals. Activity was crepuscular with two clear peaks, one in the morning and the other in the evening. The occurrence of behavioural groups was not different between the morning and evening. The frequency of aggressive behaviours was not affected by changes made to stocking density or access to food. The implications of agonistic behaviours are discussed further in relation to developing aquaculture.

This review aimed to place crustacean research on in vivo protein synthesis into a broader context, assess its potential for providing further insights into crustacean nutrition and physiology, and recommend future directions relevant to crustacean aquaculture. In crustaceans the flooding dose measurement of protein synthesis is the only method that has been used, it is relatively complex, time consuming and uses radioactive labels. Protein synthesis provides a subtle approach to assessing imbalances and deficiencies in dietary amino acid and energy. In addition, the calculation of protein synthesis retention efficiency (SRE) is recommended in order to understand and optimize parameters such as feeding regime and diet composition. For prawns, SRE was highest at optimum dietary protein content and quality. Similarly the most efficient feeding regimes in juvenile lobsters were demonstrated by the highest efficiency of retaining synthesized protein. Understanding how various abiotic and biotic factors influence protein synthesis has great potential for improving different aspects of crustacean aquaculture but very few studies have done this; better knowledge of how abiotic and biotic factors affect crustacean protein synthesis will contribute to optimising growth of crustaceans in culture.

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.

Background Atlantic salmon production in Tasmania (Southern Australia) occurs near the upper limits of the species thermal tolerance. Summer water temperatures can average over 19 °C over several weeks and have negative effects on performance and health. Liver tissue exerts important metabolic functions in thermal adaptation. With the aim of identifying mechanisms underlying liver plasticity in response to chronic elevated temperature in Atlantic salmon, label-free shotgun proteomics was used to explore quantitative protein changes after 43 days of exposure to elevated temperature. Results A total of 276 proteins were differentially (adjusted p-value

Understanding diet- and environmentally induced physiological changes in fish larvae is a major goal for the aquaculture industry. Proteomic analysis of whole fish larvae comprising multiple tissues offers considerable potential but is challenging due to the very large dynamic range of protein abundance. To extend the coverage of the larval phase of the Atlantic salmon (Salmo salar) proteome, we applied a two-step sequential extraction (SE) method, based on differential protein solubility, using a nondenaturing buffer containing 150 mM NaCl followed by a denaturing buffer containing 7 M urea and 2 M thiourea. Extracts prepared using SE and one-step direct extraction were characterized via label-free shotgun proteomics using nanoLC-MS/MS (LTQ-Orbitrap). SE partitioned the proteins into two fractions of approximately equal amounts, but with very distinct protein composition, leading to identification of ∼40% more proteins than direct extraction. This fractionation strategy enabled the most detailed characterization of the salmon larval proteome to date and provides a platform for greater understanding of physiological changes in whole fish larvae. The MS data are available via the ProteomeXchange Consortium PRIDE partner repository, dataset PXD003366.

Marine oils are important to human nutrition as the major source of docosahexaenoic acid (DHA), a key omega-3 long-chain (≥C20) polyunsaturated fatty acid (n-3 LC-PUFA) that is low or lacking in terrestrial plant or animal oils. The inclusion of fish oil as main source of n-3 LC-PUFA in aquafeeds is mostly limited by the increasing price and decreasing availability. Fish oil replacement with cheaper terrestrial plant and animal oils has considerably reduced the content of n-3 LC-PUFA in flesh of farmed Atlantic salmon. Novel DHA-enriched oils with high alpha-linolenic acid (ALA) content will be available from transgenic oilseeds plants in the near future as an alternative for dietary fish oil replacement in aquafeeds. As a preliminary validation, we formulated an oil blend (TOFX) with high DHA and ALA content using tuna oil (TO) high in DHA and the flaxseed oil (FX) high in ALA, and assessed its ability to achieve fish oil-like n-3 LC-PUFA tissue composition in Atlantic salmon smolts. We applied proteomics as an exploratory approach to understand the effects of nutritional changes on the fish liver. Comparisons were made between fish fed a fish oil-based diet (FO) and a commercial-like oil blend diet (fish oil + poultry oil, FOPO) over 89 days. Growth and feed efficiency ratio were lower on the TOFX diet. Fish muscle concentration of n-3 LC-PUFA was significantly higher for TOFX than for FOPO fish, but not higher than for FO fish, while retention efficiency of n-3 LC-PUFA was promoted by TOFX relative to FO. Proteomics analysis revealed an oxidative stress response indicative of the main adaptive physiological mechanism in TOFX fish. While specific dietary fatty acid concentrations and balances and antioxidant supplementation may need further attention, the use of an oil with a high content of DHA and ALA can enhance tissue deposition of n-3 LC-PUFA in relation to a commercially used oil blend.

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.

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.

The efficacy of photoperiod manipulation to influence growth and developmental processes is well documented in a range of temperate aquaculture species. However, the application of such techniques with tropical species requires further investigation. This preliminary 20-day study investigated the influence of continuous photoperiod on growth of barramundi (Lates calcarifer). In addition, diel plasma melatonin profiles provided a physiological measure of how the endocrine system of barramundi responded to continuous photoperiod. Juvenile barramundi (1.33 ± 0.02 g) were held in recirculation systems under 12-h light: 12-h dark (12L:12D) or 24-h light (24L:0D) with a light intensity of 1,000 lux throughout the water column. Fish from both treatments grew to more than 14 times their original weight, with final weight (24L:0D = 21.59 ± 0.85 g; 12L:12D = 19.12 ± 0.55 g), total length (24L:0D = 12.67 ± 0.14 cm; 12L:12D = 11.96 ± 0.13 cm) and specific growth rate (24L:0D = 9.60 ± 0.05% bw day−1; 12L:12D = 9.14 ± 0.06% bw day−1) being significantly higher for fish grown on 24L:0D compared with 12L:12D. There were no significant differences in feed intake (24L:0D = 226.46 ± 6.27 g; 12L:12D = 219.02 ± 5.73 g) or feed conversion ratio (24L:0D = 0.71 ± 0.06; 12L:12D = 0.80 ± 0.07) between light treatments. Barramundi held under 12L:12D exhibited diel melatonin secretion, which peaked mid-dark phase (171.83 ± 4.81 pg ml−1) followed by a gradual decrease in base levels at the onset of illumination (68.61 ± 8.77 pg ml−1). When juvenile barramundi were subjected to 24L:0D, the amplitude of peak melatonin secretion was significantly suppressed during the subjective mid-dark phase (129.71 ± 2.36 pg ml−1). This preliminary study confirmed that barramundi respond to photoperiod manipulation in a similar manner to many temperate fish species, thus demonstrating the future potential use of artificial lighting to improve growth in this species commercially.

Vegetable oils (VO) have become the predominant substitute for fish oil (FO) in aquafeeds; however, the resultant lower content of n-3 long-chain ( ≥ C20) PUFA (n-3 LC-PUFA) in fish has put their use under scrutiny. The need to investigate new oil sources exists. The present study tested the hypothesis that in Atlantic salmon (Salmo salar L.), a high intake of stearidonic acid (SDA) from Echium oil (EO) would result in increased n-3 LC-PUFA biosynthesis due to a lower requirement for Δ6 desaturase. Comparisons were made with fish fed on diets containing rapeseed oil (RO) and FO in freshwater for 112 d followed by 96 d in seawater. EO fish had higher whole-carcass SDA and eicosatetraenoic acid (ETA) in freshwater and prolonged feeding on the EO diet in seawater resulted in higher SDA, ETA, EPA and docosapentaenoic acid (DPA) compared with RO fish. Fatty acid mass balance of freshwater fish indicated higher biosynthesis of ETA and EPA in EO fish compared with fish fed on the other diets and a twofold increase in n-3 LC-PUFA synthesis compared with RO fish. In seawater, n-3 biosynthetic activity was low, with higher biosynthesis of ETA in EO fish and appearance of all desaturated and elongated products along the n-3 pathway. SDA-enriched VO are more suitable substitutes than conventional VO from a human consumer perspective due to the resulting higher SDA content, higher total n-3 and improved n-3:n-6 ratio obtained in fish, although both VO were not as effective as FO in maintaining EPA and DHA content in Atlantic salmon.

The striped trumpeter, Latris lineata, is a native fish being developed for aquaculture in Tasmania, Australia. Striped trumpeter have a long postlarval stage and rearing has been reliant on the long-term use of Artemia. Two experiments were conducted to investigate weaning strategies. The first experiment used 52 d posthatch (dph) postlarvae previously reared on Artemia from 16 to 52 dph enriched with either low or high ascorbic acid. The treatments were Artemia, a microdiet, or cofeeding. The postlarvae were reared until 67 dph. The Artemia treatment yielded significantly higher mean survival, followed by cofeeding, and the microdiet. Feeding Artemia yielded significantly heavier postlarvae and the microdiet produced significantly smaller postlarvae. A second experiment used 41 dph postlarvae and investigated the effect of cofeeding duration prior to feeding with Artemia and microdiet as controls. Cofeeding periods of 5, 10, and 15 d were tested. Cofeeding for 5 d and microdiet feeding yielded significantly poorer survival compared with Artemia. Artemia feeding yielded significantly heavier postlarvae. In both experiments, the diets did not have a significant effect on jaw morphology. These experiments are the first to examine weaning strategies for striped trumpeter postlarvae and suggest cofeeding postlarvae from 40 dph and feeding microdiet exclusively at 50 dph.

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).

The present review examines renewable sources of oils with n-3 long-chain ( ≥ C20) PUFA (n-3 LC-PUFA) as alternatives to oil from wild-caught fish in aquafeeds. Due to the increased demand for and price of wild-caught marine sources of n-3 LC-PUFA-rich oil, their effective and sustainable replacement in aquafeeds is an industry priority, especially because dietary n-3 LC-PUFA from eating fish are known to have health benefits in human beings. The benefits and challenges involved in changing dietary oil in aquaculture are highlighted and four major potential sources of n-3 LC-PUFA for aquafeeds, other than fish oil, are compared. These sources of oil, which contain n-3 LC-PUFA, specifically EPA (20 : 5n-3) and DHA (22 : 6n-3) or precursors to these key essential fatty acids, are: (1) other marine sources of oil; (2) vegetable oils that contain biosynthetic precursors, such as stearidonic acid, which may be used by fish to produce n-3 LC-PUFA; (3) single-cell oil sources of n-3 LC-PUFA; (4) vegetable oils derived from oil-seed crops that have undergone genetic modification to contain n-3 LC-PUFA. The review focuses on Atlantic salmon (Salmo salar L.), because it is the main intensively cultured finfish species and it both uses and stores large amounts of oil, in particular n-3 LC-PUFA, in the flesh.

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.

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.

High inclusion levels of dehulled lupin (Lupinus angustifolius) in salmonid diets significantly decrease growth rates. This may be caused by the high concentrations of non-starch polysaccharides including oligosaccharide (OS) in lupin. The antinutritive effects of OS have not yet been fully investigated in fish. The objective of this study was to determine the effect of enzyme supplementation of dehulled lupin-based diets on the fish performance. There were two control diets: a fish meal-based diet with no plant protein (FM) and a diet that contained 50% dehulled lupin (L). Four experimental diets based on diet L and containing four different exogenous enzyme supplements were used: diet L(E) (Energex™); diet L(B) (Bio-Feed™ Pro); diet L(α) (Alpha galactosidase™); and diet L(Mix), which contained all the enzymes. Fish were randomly stocked into tanks in duplicate groups of 38 fish, 16.58±0.169 (SE) g, and were fed twice a day for 6 weeks. The supplemented enzymes did not improve weight gain in fish fed lupin-based diets. However, mixed enzyme significantly improved Protein Efficiency Ratio (PER). Apparent digestibility of DM, CP and GE significantly improved in fish-fed L(E) diet. None of the supplemented enzymes affected digestive tract indices or carcass composition. Surprisingly, weight gain was significantly higher in fish-fed L(α), L(E) and L(Mix) diets as compared with FM diet. Feed intake was significantly higher in fish-fed L, L(α) and L(E) diets compared with the FM diet. It is concluded that storing of lupin kernel under a suitable condition may have partially hidden the positive effects of exogenous enzymes through activating the endogenous enzymes

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.

Feeds and feeding are crucial to hatchery success. In freshwater, commercial manufactured feeds are successfully fed at first-feeding to many important aquaculture species. These fish typically have large larvae with well-developed digestive tracts and include carp, salmonids and catfish. Almost all marine larvae require a period of feeding on live feeds and can only use manufactured feeds several days after hatch when the larvae have grown larger and have a more advanced digestive tract. Different live feeds and manufactured feeds are introduced in relation to the changing nutritional physiology of larval fish. Current hatchery feeding regimes are outlined for several key species selected to represent different types of fish and aquaculture systems. Future developments and trends will be to: understand quantitative nutrient requirements of larval and early juvenile fish; reduce reliance of marine species for live feeds by increasing co-feeding and starting this earlier in the larval cycle; eventually replace live feeds with manufactured feeds (although this is some time away); adopt approaches for the rapid technology transfer across the multitude of species being investigated as candidates for aquaculture.

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

Previous studies have demonstrated that beta-glucans stimulate Atlantic salmon, Salmo salar L., head kidney macrophages both in vitro and in vivo and increase protection against various pathogens. Based on our previous work that showed potent immunostimulatory CpG motif-containing oligodeoxynucleotides increased resistance to amoebic gill disease (AGD), the present study investigated the immunostimulatory effects of three commercial beta-glucan-containing feeds and their ability to increase resistance to AGD. All three commercial beta-glucans were able to stimulate the respiratory burst activity of Atlantic salmon head kidney macrophages in vitro, albeit at different times and concentrations. However, dietary incorporation of the beta-glucans was unable to stimulate the in vivo respiratory burst activity of head kidney macrophages, or serum lysozyme production, and did not increase resistance against AGD. However, this trial showed for the first time that a small subpopulation of Atlantic salmon subjected to a severe AGD infection was able to resist becoming heavily infected and furthermore survive the challenge.

A recently developed radioimmunoassay (RIA) for measuring insulin-like growth factor (IGF-I) in a variety of fish species was used to investigate the correlation between growth rate and circulating IGF-I concentrations of barramundi (Lates calcarifer), Atlantic salmon (Salmo salar) and Southern Bluefin tuna (Thunnus maccoyii). Plasma IGF-I concentration significantly increased with increasing ration size in barramundi and IGF-I concentration was positively correlated to growth rates obtained in Atlantic salmon (r2=0.67) and barramundi (r2=0.65) when fed a variety of diet formulations. IGF-I was also positively correlated to protein concentration (r2=0.59). This evidence suggested that measuring IGF-I concentration may provide a useful tool for monitoring fish growth rate and also as a method to rapidly assess different aquaculture diets. However, no such correlation was demonstrated in the tuna study probably due to seasonal cooling of sea surface temperature shortly before blood was sampled. Thus, some recommendations for the design and sampling strategy of nutritional trials where IGF-I concentrations are measured are discussed

The replacement of fish oil with a dried product made from thraustochytrid culture, a marine microorganism, in canola-oil-based diets for Atlantic salmon was investigated. Salmon (37 g) were fed for 51 days on diets containing only canola oil, canola oil and fish oil, or canola oil and the thraustochytrid. There were no significant differences in final weight (106.1 +/- 1.1 g), weight gain (69.6 +/- 1.1 g), feed consumption (16.5 +/- 0.2 mg dry matter g(-1) d(-1)), feed efficiency ratio (1.15 +/- 0.03 g (g-1)), or productive protein value (51.2% +/- 1.7%) between the diets. Nor were there any significant differences in whole-body chemical composition, organ somatic indices, or measures of immune function. However, following transfer to seawater and 2 challenges with Vibrio anguillarum, cumulative mortality was significantly lower in fish fed some fish oil than in those fed the 2 diets containing no fish oil. In conclusion, the thraustochytrid had no detrimental effects on the performance of salmon but, at the current inclusion of 10%, failed to confer the same effect as fish oil under challenging conditions.

The study aimed to test the similarity between apparent digestibility coefficients (ADC) calculated using either yttrium oxide or cholestane. Atlantic salmon were fed three diets containing a different mix of oil sources: diets contained only canola oil (CO), canola oil and fish oil (CFO), or canola oil and thraustochytrid meal (CTH) (a marine microorganism with potential as an alternative oil source). Both markers were concentrated by the same amount in the faeces compared to the diets. ADC values using cholestane tended to be higher than yttrium, and there was a significant marker effect for crude protein, energy, total lipid and triacylglycerol. Although statistically significant the marker effect was due to numerically small differences in ADC values and probably of limited biological significance. ADC values for the majority of fatty acids did not show marker effects. Consequently, it was concluded that the broad similarity in the digestibility of lipid components between markers validated the use of cholestane for calculating lipid digestibility in Atlantic salmon.

The availability of formulated diets is considered economically imperative if rock lobster aquaculture, based on the collection and ongrowing of puerulus, is to progress. Central to the development of diets is an understanding of the nutritional requirements of the species. This study determined the effect of different dietary carbohydrate/lipid ratios (17:1, 5:1, 2:1, 0.8:1) on the growth and nutritional condition of juvenile southern rock lobsters, Jasus edwardsii, by measuring standard growth parameters, proximate composition of the whole body and digestive gland, and from a histological investigation of the digestive gland. Four replicate groups of eight lobsters (initial weight 5.08±0.98 g (mean±S.D.)) per diet treatment were held in 50 l tanks, in a recirculating system at 18 °C for 84 days. Maximum growth and the highest levels of lipid and dry matter in digestive glands and whole bodies was found in lobsters fed a diet containing 27% carbohydrate and 13.5% lipid (2:1 ratio) suggesting that of the four experimental diets, this diet provided the best balance of lipid and carbohydrate. Digestive gland histology supported this conclusion and lobsters fed low carbohydrate, high lipid diets were in the best nutritional condition, with high lipid accumulation, and structurally sound epithelial cells. Digestive gland epithelial cells of lobsters fed the high carbohydrate, low lipid diets were compressed, of inconsistent shape and size, with low lipid accumulation. Histology is therefore seen as a feasible method, in addition to growth and proximate composition data, to further examine the effect of diets in nutritional studies of crustaceans.

The effect of feed availability (ration level and feeding frequency) on the culture performance of the juvenile (5–22 g) southern rock lobster Jasus edwardsii was examined to determine whether multiple daily feeding of a formulated feed would stimulate growth. Furthermore, the relationships between feed availability, agonistic behaviour, dominance, growth and survival were examined. A total of 252 lobsters (mean weight 5.26 g) were stocked into 28 black 52-l tanks at a density of nine lobsters per tank (42 m −2 ) and maintained at a temperature of 18.8 °C in a recirculating seawater system for 119 days. Lobsters were fed with high (4% BW day −1 ) or low (0.5% BW day −1 ) rations divided between one, two or four meals per day. These regimes were compared to a regime of fresh mussels ( Mytilus edulis ) fed to excess once per day. Feeding lobsters with a high-ration level, 4 day −1 , made no significant ( P >0.05) improvements in specific growth rate (SGR) (0.77–0.82% BW day −1 ), survival (75–84%) or biomass yields (96–102 g) compared to feeding 1 or 2 day −1 . Low-ration-fed lobsters had a higher final mean weight (17.5–20.9 g) compared to high-ration lobsters (13.4–14.3 g), however, survival of lobsters that were fed with low ration of 4 day −1 (41%) was significantly ( P P Lobsters were size-ranked (g) to determine the effects of feed competition on the growth and survival of individuals of different rank. The ability and/or motivation of the largest lobsters to maintain their size status increased as feed availability decreased, suggesting that feed restrictions increased the strength of dominance. Size-ranking also demonstrated that small lobsters were more vulnerable to being cannibalised, especially when the feed-ration level was low. Feed competition was consistent with the concept of economic defensibility, predicting that levels of agonistic behaviour are highest when a low ration was patterned into smaller, more easily defended meals (low-ration fed, 4 day −1 ). In contrast, feed competition and agonistic behaviour were rarely observed when feed was freely available (high-ration fed, 4 day −1 ). The high levels of cannibalism of small size-ranked lobsters meant that assessing growth depensation was not a useful approach to the evaluation of the relationships between competition and growth in groups. The implications for J. edwardsii culture are that feeding high-ration levels of formulated feeds, more than once daily, reduces feed competition and incidence of agonistic behaviour. However, there appear to have few benefits in terms of growth or survival. The recommendation from this study is to feed lobsters once daily to excess after dusk.

The utilization of dehulled lupin as a partial replacement for fish meal was studied in diets of rainbow trout. Fish were fed diets with 0%, 10%, 20%, 30%, 40% and 50% of dehulled lupin, at a daily feeding rate of 2% body weight for 8 weeks at 15 ± 0.5 °C. Growth performance generally decreased with increasing dehulled lupin in the diet (R2 = 0.81, P

Development of a formulated pellet to replace ‘bait’ fish in farmed southern bluefin tuna (SBT), Thunnus maccoyii (Castelnau), feeds is in progress; however, inherent difficulties have been encountered in conducting large-scale growth trials to evaluate experimental pellet quality. Consequently, alternative methods are being investigated to develop a suitable feed more rapidly. This work explored whether Atlantic salmon, Salmo salar L., could be used as a ‘surrogate’ species for nutrition research on SBT by screening experimental SBT feeds. Atlantic salmon (initial mean weight 161.4 g) were fed a commercial salmon feed (Com.Sal), a commercial northern bluefin tuna feed (Com.NBT), one of three experimental SBT feeds (CRC-A, -B, -C) or dry pelleted pilchards for 42 days, at which time growth was assessed. In vivo and in vitro protein digestibility of the feeds was also evaluated. Weight gain of Atlantic salmon fed Com.Sal (99.8 g) and Com.NBT (93.5 g) were found to be significantly (P

This study was undertaken to assess whether collection of faeces by a stripping method was suitable for measuring digestibility in large seawater Atlantic salmon of up to 5 kg. Experiments were conducted to determine the effects on the apparent digestibility coefficient (ADC) of faecal collection technique, urine and mucus contamination of faecal samples, immediate repeated sampling on individuals, stripping pressure during the collection of faeces, dorso-flexion of the tail prior to faecal sample collection, variation between individual fish and section of gut sampled. Faecal collection by rectal suction and dissection was compared with the stripping collection method. Rectal suction produced comparable results to stripping; however, ADC for crude protein was significantly ( P P P

Many studies with fin fish have demonstrated the potential to use alternative dietary protein sources to fish meal based on growth responses, although these trials mostly neglect to determine if such protein sources affect immune function. This study investigated the effect of fish meal replacement with dehulled lupin meal (LPN) or hydrolysed poultry feather meal (FTH). Atlantic salmon (Salmo salarL.) parr were supplied isonitrogenous and isoenergetic diets with 40% of the dietary protein provided by LPN or FTH, or 400 g/kg of the dietary protein provided equally by LPN and FTH (MIX). A diet mainly containing fish-meal protein acted as a control (CON). Growth, immune function, blood chemistry and disease resistance were assessed after 56 days. Significant differences (P< 0·05) in weight gain were detected between Atlantic salmon given the CON and FTH diets, whilst those salmon given LPN and MIX did not differ from any other. Productive protein values were significantly lower (P< 0·01) for salmon on FTH compared with those on CON and MIX. Immune function (as assessed by lysozyme, antiprotease, neutrophil oxygen radical production and plasma total immunoglobulin) and blood chemistry (as assessed by plasma total protein and glucose) were not significantly (P> 0·05) affected by any diet. Mortality rates of Atlantic salmon challenged with Vibrio anguillarum were not influenced by diet. These data suggest Atlantic salmon could be supplied diets with the fish meal component reduced to supply approximately 600 g/kg of the total protein, with the remaining 400 g/kg supplied by dehulled lupin meal or a combined dehulled lupin and hydrolysed poultry feather meal without any adverse effects on growth, immune function or blood chemistry.