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Connecting the selective forces that drive the evolution of phenotypes to their underlying genotypes is key to understanding adaptation, but such connections are rarely tested experimentally. Threespine stickleback (Gasterosteus aculeatus) are a powerful model for such tests because genotypes that underlie putatively adaptive traits have been identified. For example, a regulatory mutation in the Ectodysplasin (Eda) gene causes a reduction in the number of bony armor plates, which occurs rapidly and repeatedly when marine sticklebacks invade freshwater. However, the source of selection on plate loss in freshwater is unknown. Here, we tested whether dietary reduction of phosphorus can account for selection on plate loss due to a growth advantage of low-plated fish in freshwater. We crossed marine fish heterozygous for the 16 kilobase freshwater Eda haplotype and compared the growth of offspring with different genotypes under contrasting levels of dietary phosphorus in both saltwater and freshwater. Eda genotype was not associated with growth differences in any treatment, or with mechanisms that could mitigate the impacts of phosphorus limitation, such as differential phosphorus deposition, phosphorus excretion, or intestine length. This study highlights the importance of experimentally testing the putative selective forces acting on phenotypes and their underlying genotypes in the wild.

The effects of feeding an 80% plant protein diet, with and without fish protein hydrolysate (FPH) supplementation, on the growth and gut health of Atlantic salmon were investigated. Fish were fed either (A) a control diet containing 35% fishmeal, (B) an 80% plant protein diet with 15% fishmeal, (C) an 80% plant protein diet with 5% fishmeal and 10% partly hydrolysed protein, or (D) an 80% plant protein diet with 5% fishmeal and 10% soluble protein hydrolysate. Fish on the 80% plant- 15% fishmeal diet were significantly smaller than fish in the other dietary groups. However, partly-hydrolysed protein supplementation allowed fish to grow as well as fish fed the control 35% fishmeal diet. Fish fed the FPH diets (diets C and D) had significantly higher levels of amino acids in their blood, including 48% and 27% more branched chain amino acids compared to fish on the 35% fishmeal diet, respectively. Plant protein significantly altered gut microbial composition, significantly decreasing α-diversity. Spirochaetes and the families Moritellaceae, Psychromonadaceae, Helicobacteraceae and Bacteroidaceae were all found at significantly lower abundances in the groups fed 80% plant protein diets compared to the control fishmeal diet.

A protein gap exists within the supply of fish feed ingredients due to intensifying global aquaculture production and demands. This is distinctly acute in salmonid farming where protein requirements are higher to other aquatic farmed species. In pursuit of a viable alternative, an eight-week feeding trial was conducted to evaluate the feasibility of including reared black soldier fly (BSF, Hermetia illucens) larvae into rainbow trout (Oncorhynchus mykiss) diets. Five diets were formulated: a fish meal-based basal diet (CTRL), two diets of BSF incorporation at 15 and 30% (BSF15; BSF30), and two diets at the same incorporation level with the addition of a supplementary protease enzyme (BSF15P; BSF30P) assigned to test potential dietary enhancement. No significant growth performance between the dietary treatments was observed. The fish condition factor in BSF30 was higher than BSF30P (P=0.025). Fillets showed increased muscle yellowness as dietary BSF increased (P=0.004). Trout fed BSF displayed significantly lower lipid peroxidation post-harvest (P

The microbiota in the gastrointestinal tract of any species is shaped by internal and external cues in addition to random events which can be difficult to disentangle from a range of interacting variables. Estimating ecological assembly processes can help elucidate these factors. In our study, farmed Atlantic cod (Gadus morhua) were fed a diet of 10% macroalgae supplement (Ulva rigida species [ULVA] or Ascophyllum nodosum [ASCO] or a non-amended control diet [CTRL]) over a 12-week period and the ecological assembly processes quantified. The CTRL samples showed selection (variable selection - divergence in communities related to selective environmental conditions) as a key assembly process, while dispersal limitation (limited movement results in divergent communities through stochastic processes) was a driver of the gut microbiome for fish fed the macroalgae supplemented diet at Week 12 (i.e., ASCO and ULVA). Fish from the ASCO grouping diverged into ASCO_N (normal) and ASCO_LG (lower growth), where ASCO_LG individuals found the diet unpalatable. The recruitment of new taxa over time was altered in the ASCO_LG fish, with the gut microbiome showing phylogenetic under dispersion (nepotistic recruitment of species). Finally, the gut microbiome (CTRL and ULVA only) showed increasing robustness to taxonomic disturbance over time and an increase in functional redundancy. This study advances our understanding of the ecological assembly and succession in the hindgut of juvenile Atlantic cod across dietary regimes. Understanding the processes driving ecological assembly in the gut microbiome, in fish research specifically, could allow us to manipulate the microbiome for improved health or resilience to disease for improved aquaculture production.

A feeding trial was conducted to evaluate the potential of dietary supplementation of autolysed brewer's yeast (AY) on African catfish. The catfish (22.5 ± 1.15 g/fish, 20 fish 33 L/tank) were fed with either of diets (390 g/kg crude protein, 140 g/kg lipid) supplemented with 0, 3, 6 or 10 g/kg AY (n = 3). After 49 days of feeding, the final body weight and metabolic growth rate of the catfish fed 3 g/kg AY (3‐AY) diet were higher than those fed the control diet (p .05) in intestinal perimeter ratio. However, an elevated (p

Background Aquaculture successfully meets global food demands for many fish species. However, aquaculture production of Atlantic cod (Gadus morhua) is just 2.5% of total market production. For cod farming to be a viable economic venture specific challenges on how to increase growth, health and farming productivity need to be addressed. Feed ingredients play a key role here. Macroalgae (seaweeds) have been suggested as a functional feed supplement with both health and economic benefits for terrestrial farmed animals and fish. The impact of such dietary supplements to cod gut integrity and microbiota, which contribute to overall fish robustness is unknown. The objective of this study was to supplement the diet of juvenile Atlantic cod with macroalgae and determine the impacts on fish condition and growth, gut morphology and hindgut microbiota composition (16S rRNA amplicon sequencing). Fish were fed one of three diets: control (no macroalgal inclusion), 10% inclusion of either egg wrack (Ascophyllum nodosum) or sea lettuce (Ulva rigida) macroalgae in a 12-week trial. Results The results demonstrated there was no significant difference in fish condition, gut morphology or hindgut microbiota between the U. rigida supplemented fish group and the control group at any time-point. This trend was not observed with the A. nodosum treatment. Fish within this group were further categorised as either ‘Normal’ or ‘Lower Growth’. ‘Lower Growth’ individuals found the diet unpalatable resulting in reduced weight and condition factor combined with an altered gut morphology and microbiome relative to the other treatments. Excluding this group, our results show that the hindgut microbiota was largely driven by temporal pressures with the microbial communities becoming more similar over time irrespective of dietary treatment. The core microbiome at the final time-point consisted of the orders Vibrionales (Vibrio and Photobacterium), Bacteroidales (Bacteroidetes and Macellibacteroides) and Clostridiales (Lachnoclostridium). Conclusions Our study indicates that U. rigida macroalgae can be supplemented at 10% inclusion levels in the diet of juvenile farmed Atlantic cod without any impact on fish condition or hindgut microbial community structure. We also conclude that 10% dietary inclusion of A. nodosum is not a suitable feed supplement in a farmed cod diet.

A 10-week feeding trial was conducted to evaluate the effects of partially substituting soya protein concentrate (SPC), with white lupin (Lupinus albus) meal in carp (Cyprinus carpio) diets. This study further investigated the dietary inclusion of a solid-state fermentation (SSF) product of Aspergillus niger in tandem with SPC replacement. Six experimental diets were produced to be isonitrogenous (42%), isolipdic (8%) and isoenergetic (19 MJ kg−1). Four diets were formulated to have 12.5 and 25% substitution of SPC using lupin meal, and with and without a supplement of 0.1% of SSF. An additional two diets were designed to serve as a basal reference with no SPC replacement, but one supplemented with 0.1% SSF inclusion. The results of this study showed that SPC can be replaced with up to 25% white lupin meal in carp diets, without reduction of growth performance, feed utilisation, body composition, gut integrity or health. The addition of SSF to the test diets enhanced growth performance (specific growth rate, P

Bacteria fromthe Vibriogenus are autochthonous to aquatic environments and ubiquitous in aquaculture production systems. Many Vibrio species are non-pathogenic and can be commonly found in healthy farmed aquatic animals. However, some Vibrio species and strains are pathogenic leading to a variety of 'vibriosis' diseases. These diseases can have a significant negative impact on animal production, including farmed crustaceans such as shrimps, lobsters, and crabs. As such, vibriosis can pose a threat to meeting growing food demand and global food security. Preventive management is essential to avoid the onset of vibriosis. This includes a robust health management plan, the use of prophylaxis and treatment measures, and enhancing animal health through nutrition. Furthermore, the use of probiotics, prebiotics, synbiotics, quorum sensing disruption, green water, biofloc, bacteriophages, and immune priming could also play a role in preventing and controlling a vibriosis outbreak. This review aims to inform and update the reader about the current state of knowledge about Vibrio and associated vibriosis in farmed crustaceans (i.e. shrimp, lobster, and crabs). Furthermore, the review will identify potential knowledge gaps in the literature, which serves as a basis for future research priorities.

Macroalgae, commonly known as seaweed, offer a novel and added‐value dietary ingredient in formulated diets for fish. Production of biomass can be achieved without reliance on expensive arable land, as seaweed may be collected from coastal regions or farmed. There are three taxonomic groups represented by the term ‘macroalgae’: Rhodophyta (red), Chlorophyta (green) and Phaeophyta (brown). Like terrestrial plants, nutritional content in macroalgae can vary greatly amongst species, genera, divisions, seasons and locations. Aside from their basic nutritional value, seaweeds contain a number of pigments, defensive and storage compounds, and secondary metabolites that could have beneficial effects on farmed fish. This review appraises the beneficial qualities of these macroalgae compounds and their potential for exploitation in commercial finfish feeds. The current knowledge of the effects of macroalgae inclusion in finfish diets is also addressed. From these >50 fish feeding studies that were analysed, enhancing trends in fish growth, physiology, stress resistance, immune system and fillet muscle quality were reported. However, only a small fraction of algal species have so far been investigated as potential components in finfish diets, and furthermore, this review has identified a number of knowledge gaps that current research has yet to address. To conclude, an appraisal is made of the possible technologies employed to exploit seaweeds to an industrial level through stabilising the algal meal, enhancing the digestibility and functional food properties.

Invertebrate meals (e.g. polychaetes and insects) present novel and sustainable high-quality nutrient sources for use in fish feed formulations. To test this innovative source, an eleven-week feeding trial was conducted evaluating the effects of replacing the fishmeal (FM) component as an example of a superior protein source (FM CTRL) with ragworm meal (RW, Nereis virens) and/or silkworm pupae (SWP, Bombyx mori) in mirror carp (Cyprinus carpio) diets. Three experimental diets with partial replacement of FM (diets: RW + FM, SWP + FM and RW + SWP + FM) were formulated. All diets were formulated to be iso-nitrogenous, iso-lipidic and iso-energetic. Growth performance and feed utilization indices were assessed, and the feeding trial concluded with the analysis of haematological parameters to provide an indication of carp physiological and health status. Mean weight gain was greatest in mirror carp fed RW + FM (60.83 fish−1 day−1; P < 0.05 vs. all other diets) followed by SWP + FM (40.62 g fish−1 day−1; P < 0.05 vs. all other diets). The least weight gain was achieved in fish fed FM + SWP + RW+ and FM CTRL (34.34 and 33.96 g fish−1 day−1, respectively; not significantly different from each other). Fish fed on RW + FM diet had significantly lower plasma ammonia concentrations than any other dietary groups (P = 0.04). Mirror carp fed on SWP + FM diet (111.52 units mL−1) were observed to have a marked enhancement in alternative complement activity than FM CTRL (79.21 units mL−1, P = 0.041). Both ragworm and silkworm pupae meal present attractive sustainable functional feed component in carp diets, with benefits on enhancing growth performance and specific physiological parameters.

BackgroundStable isotope analysis of single amino acids (AA) is usually applied in food web studies for tracing biosynthetic origins of AA carbon backbones and establishing trophic positions of consumers, but the method is also showing promise for characterizing quantity and quality of dietary lipids and carbohydrates.MethodsTo investigate whether changes in high- and low-digestible carbohydrates affectδ13C values of glycolytic AA, i.e., AA carbon backbones sourced from the glycolytic pathway, we compared Atlantic salmon (Salmo salar) from a feeding experiment with and without dietary inclusion of the red macroalgaPalmaria palmata. The Control and experimental diets had similar relative proportions of macronutrients, but their ingredients differed; in the experimental treatment, 15%Palmariainclusion substituted proteins from fishmeal and carbohydrates from corn starch.ResultsWe found that13C values of the glycolytic AA were highly sensitive to substitution of corn starch withPalmaria. Theδ13C offsets of glycolytic AA between salmon and their diets were significantly greater in thePalmariainclusion than Control treatment. This greater offset can be attributed to the different utilization of high- vs. low-digestible carbohydrate sources, i.e., corn starch vs.Palmaria, in the two treatments, and metabolic routing of dietary lipids. In addition, similarδ13C values of essential AA between treatments indicate similar nutrient assimilation efficiency for all terrestrial (pea protein concentrate and wheat gluten meal) and marine (fishmeal and red alga) derived protein sources. These results show thatδ13CAAanalysis is a promising tool for improving our understanding of how carnivorous fish utilize macronutrient and route metabolic intermediates to tissue.

Supplementation of salmon (Salmo salar) diets with Ulva rigida (UR; 0, 5, 10, and 15% UR) or synthetic astaxanthin (positive control, PC) for 19-weeks preslaughter on quality indices of fresh (raw) salmon fillets was examined. Susceptibility of salmon fillets/homogenates to oxidative stress conditions (cooking/iron-ascorbate induced oxidation) was also measured. In salmon fillets stored in modified atmosphere packs (MAP; 60% N2:40% CO2) for up to 15 days at 4oC, U. rigida increased surface “−a*” greenness and “b*” yellowness values in a dose-dependent manner resulting in a final yellow/orange flesh color. Proximate composition, pH, and lipid oxidation (fresh, cooked, and fillet homogenates) were unaffected by dietary addition of U. rigida. On Day 12, 5% UR psychrotrophic bacterial growth was lower than controls. Salmon fed 5% UR did not influence “eating quality” sensory descriptors (texture, odor, oxidation flavor, and overall acceptability) in cooked salmon fillets compared to 0% UR. Higher leve...

A feeding study was carried out for fourteen weeks to evaluate the effects of partial inclusion of 5, 10 and 15 % of dillisk, Palmaria palmata, into formulated Atlantic salmon (Salmo salar) diets. A further fourth diet was produced without the presence of algae and was used as a basal reference diet. All the four diets were formulated to be iso-nitrogenous (40 %), iso-lipidic (25 %) and iso-energetic (26 MJ kg−1). Salmon growth (final body weight, weight gain, feed conversion ratio (FCR), specific growth rate (SGR)) were comparable across algal and control diets, with no significant differences amongst the treatments (P > 0.05). Comparisons of liver weight, viscera weight and viscerosomatic index (VSI) also suggested that the macroalgal inclusion did not affect fish growth (P > 0.05). Fish health indicators across haematological, immunological and hepatic function were generally similar between the experimental diets. The exceptions to this pattern included a significant decrease in alanine transaminase activity (P

A feeding trial was conducted to evaluate the effects of replacing fish meal (FM) with bacterial protein (BP) in African catfish (Clarias gariepinus) diets. Four iso‑nitrogenous (369 g kg−1) and isolipidic (142 g kg−1) diets were formulated to replace graded levels (0%, 30%, 60% and 100%) of FM protein resulting in a dietary inclusion level of 0, 27.90, 55.70 and 93.00 g kg−1 BP. Test diets were fed to the catfish (initial weight 18.17 ± 0.25 g fish−1, n = 20) in three replicate tanks. After 56 days of feeding, catfish fed with 30% BP diet had outperformed (P 0.05). While histological analysis of the catfish mid-intestine showed intact epithelial barriers with extensive mucosal folds extending into the lumen. The intestinal perimeter ratio of fish fed with 30% BP diet was higher (+32%) than those of the dietary control group (P 0.05). Indication of the liver health status was measured through serum aspartate transaminase, alanine transaminase, and alkaline phosphatase activities, and hepatocyte density, which remains statistically unchanged between the dietary groups (P > 0.05). Overall, the results show that BP can replace FM wholly or partly in African catfish (C. gariepinus) diet, without compromising growth performance, haemato-biochemistry, intestinal integrity, or liver functionality.

Aquaculture is the most rapidly expanding food production sector and this trend is projected to continue in the coming decades. Intensification of farming methods alongside a tendency for farming higher trophic level species has led to concerns over nutrient loading of coastal waters. Where this is the case, Integrated Multi-Trophic Aquaculture (IMTA) has been proposed as a best-practice management option for reducing environmental impact. Fed aquaculture can also affect metal concentrations of surrounding biota by acting as a point source of contamination or by altering the abiotic environment in a manner that affects the capacity of organisms to accumulate metals. Seaweeds are integral to IMTA in providing the inorganic nutrient extraction component of the system, however it is unknown whether their close proximity to other aquaculture operations facilitates increased metal accumulation. As a result, the effect of cultivation and growth environment on accumulation of metals in the kelp Laminaria digitata (Hudson) J.V. Lamouroux was investigated, providing the first comparative experimental data examining the effect of multi-species cultivation on trace metal content of macroalgae. Thalli of L. digitata growing wild, cultivated as a single species (mono-cultivated), and cultivated alongside organic Irish salmon aquaculture facilities (IMTA) were analysed for metal content (As, Ba, Cd, Co, Cu, Mn, Sb, V, Zn). Cultivation in an IMTA context raised the content of Cu, Mn and V relative to that in mono-cultivated seaweeds however concentrations of metals were within the range of those from algae collected from undisturbed wild populations. Metal levels in the seaweeds do not pose a concern over inclusion as a dietary component with the possible exception of arsenic that exceeded some legislative limits. The results of this study provide novel information that can inform policy and sustainable aquaculture management practices aimed at reducing contamination of the aquatic environment and the impact on consumers. Statement of relevance This study provides the first comparative investigation of metals in seaweed from different cultivation environments and can be used to support best-practice management decisions involving IMTA. Laminaria digitata metal content was marginally increased for copper, manganese and vanadium at IMTA sites. Vanadium and antimony (emerging contaminants) in the commercially important seaweed L. digitata are reported for the first time.

BACKGROUND The use of Palmaria palmata (PP) as a natural ingredient in farmed Atlantic salmon diets was investigated. The effect of salmon diet supplementation with P. palmata (0, 5, 10 and 15%) or synthetic astaxanthin (positive control, PC) for 16 weeks pre-slaughter on quality indices of fresh salmon fillets was examined. The susceptibility of salmon fillets/homogenates to oxidative stress conditions was also measured. RESULTS In salmon fillets stored in modified atmosphere packs (60% N2/40% CO2) for up to 15 days at 4 °C, P. palmata increased surface −a* (greenness) and b* (yellowness) values in a dose-dependent manner, resulting in a final yellow/orange flesh colour. In general, the dietary addition of P. palmata had no effect on pH, lipid oxidation (fresh, cooked and fillet homogenates) and microbiological status. ‘Eating quality’ sensory descriptors (texture, odour and oxidation flavour) in cooked salmon fillets were not influenced by dietary P. palmata. Salmon fed 5% PP showed increased overall acceptability compared with those fed PC and 0% PP. CONCLUSION Dietary P. palmata was ineffective at providing red coloration in salmon fillets, but pigment deposition enhanced fillets with a yellow/orange colour. Carotenoids from P. palmata may prove to be a natural pigment alternative to canthaxanthin in salmon feeds. © 2014 Society of Chemical Industry

Enrichment of nutrients and metals in seawater associated with anthropogenic activities can threaten aquatic ecosystems. Consequently, nutrient and metal concentrations are parameters used to define water quality. The European Union's Water Framework Directive (WFD) goes further than a contaminant-based approach and utilises indices to assess the Ecological Status (ES) of transitional water bodies (e.g. estuaries and lagoons). One assessment is based upon the abundance of opportunistic Ulva species, as an indication of eutrophication. The objective of this study was to characterise Ireland's Ulva blooms through the use of WFD assessment, metal concentrations and taxonomic identity. Furthermore, the study assessed whether the ecological assessment is related to the metal composition in the Ulva. WFD algal bloom assessment revealed that the largest surveyed blooms had an estimated biomass of 2164 metric tonnes (w/w). DNA sequences identified biomass from all locations as Ulva rigida, with the exception of New Quay, which was Ulva rotundata. Some blooms contained significant amounts of As, Cu, Cr, Pb and Sn. The results showed that all metal concentrations had a negative relationship (except Se) with the Ecological Quality Ratio (EQR). However, only in the case of Mn were these differences significant (p = 0.038). Overall, the metal composition and concentrations found in Ulva were site dependent, and not clearly related to the ES. Nevertheless, sites with a moderate or poor ES had a higher variability in the metals levels than in estuaries with a high ES.