Juvenile Turbot Research Articles

Dietary replacement of fishmeal by corn distillers dried grains with solubles (DDGS) in diets for turbot (Scophthalmus maximus, Linneaus, 1758) Juveniles

The aim of this study was to determine the potential of corn distillers dried grain with solubles (DDGS) to partially replace fishmeal (FM) in practical diets for turbot. For that purpose, a control diet was formulated to include 40% FM and a mixture of plant protein ingredients (soybean meal, corn gluten, and wheat gluten). Three other diets were formulated based on the control but with 10, 17.5, or 25% of DDGS replacing FM. Diets were tested in triplicate, in an 84-days growth trial with juveniles of 29 g initial body weight. Feed intake was not affected by diet composition, but growth and feed efficiency linearly decreased with the increase of dietary DDGS level. Whole-body dry matter and protein contents were not affected by diet composition, but lipid and energy content were higher in fish fed the control diet than the 17.5DDGS and 25DDGS diets and the 25DDGS diet, respectively. The apparent digestibility coefficients (ADCs) of protein and amino acids were similar among diets, while the ADCs of energy decreased with the increase of dietary DDGS level. Digestive amylase and lipase activities in posterior intestine were lower in fish fed the 17.5DDGS and 25DDGS diets than the control diet, while proteases activity was not affected by diet. No differences among dietary treatments were observed on plasma glucose, but plasma total protein, albumin, triglycerides, and cholesterol were lower in fish fed the DDGS diets. Activity of key enzymes of glycolysis, gluconeogenesis, and lipogenesis was not affected by diet composition, but activity of alanine aminotransferase increased with the increase of dietary DDGS. Moreover, oxidative status of liver and intestine was not affected by dietary treatments, but susceptibility to oxidative stress was higher in the intestine than in the liver. Overall, it is concluded that replacing FM by DDGS in practical diets for turbot juvenile reduced growth performance and impaired overall nitrogen and energy metabolism.

Citric acid as a functional supplement in diets for juvenile turbot, Scophthalmus maximus L.: Effects on phosphorus discharge, growth performance, and intestinal health

The present study was conducted to investigate the suitability of citric acid as a feed additive for juvenile turbot (Scophthalmus maximus) to reduce phosphorus (P) excretion. A practical diet with similar profile as commercial diet was used as the positive control (C-P). C-P diet had no inorganic P supplementations, which was used as the negative control (C-0). Two citric acid supplemented diets, C-1.5 and C-3.0, were formulated by incorporating 1.5% and 3.0% citric acid into the C-0 diet, respectively. Each diet was fed to triplicate groups of 30 fish. The feeding trial lasted for 12 weeks. Turbot fed different diets showed similar growth performance, feed utilization efficiency and whole-body composition. Compared with group C-0, the pH of stomach contents in group C-3.0 was significantly lower while the pepsin activity and apparent digestibility coefficient of P in this group were notably higher. Diet C-3.0 resulted in the highest P retention, which was significantly higher compared to diet C-P but not to diet C-0. Compared to both control diets, citric acid supplemented diets significantly increased the activity of pepsin. No diet-related difference was observed in the blood biochemistry, nor in the histology and bacterial community profile of distal intestine. In summary, dietary inclusion of 3% citric acid markedly improved the bioavailability of P, without compromising intestinal function and health of fish. Citric acid seemed to be a promising feed additive for aqua-feeds to reduce P discharge into environment.

Soya-saponins induce intestinal inflammation and barrier dysfunction in juvenile turbot (Scophthalmus maximus)

Soybean meal-induced enteritis (SBMIE) is a well-described condition in the distal intestine (DI) of several cultured fish species, but the exact cause is still unclear. The work on Atlantic salmon and zebrafish suggested soya-saponins, as heat-stable anti-nutritional factors in soybean meal, are the major causal agents. However, this conclusion was not supported by the research on some other fish, such as gilthead sea bream and European sea bass. Our previous work proved that soybean could induce SBMIE on turbot and the present work aimed to investigate whether soya-saponins alone could cause SBMIE and the effects of soya-saponins on the intestinal barrier function in juvenile turbot. Turbots with initial weight 11.4 ± 0.02 g were fed one of four fishmeal-based diets containing graded levels of soya-saponins (0, 2.5, 7.5, 15 g kg−1) for 8 weeks. At the end of the trial, all fish were weighed and plasma was obtained for diamine oxidase (DAO) activity and d-lactate level analysis and DI was sampled for histological evaluation and quantification of antioxidant parameters and inflammatory marker genes. The activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and intestinal glutathione level were selected to evaluated intestinal antioxidant system. The distal intestinal epithelial cell (IEC) proliferation and apoptosis were investigated by proliferating cell nuclear antigen (PCNA) labelling and TdT-mediated dUTP nick end labeling (TUNEL), respectively. The results showed that soya-saponins caused significantly dose-dependent decrease in the growth performance and nutrient utilization (p < 0.05). Enteritis developed in DI of the fish fed diet containing soya-saponins. Significantly dose-dependent increases in severity of the inflammation concomitant with up-regulated expression of il-1β, il-8, and tnf-α, increased IEC proliferation and apoptosis, and decreases in selected antioxidant parameters were detected (p < 0.05). The epithelial permeability (evaluated by the plasma DAO activity and d-lactate level) was significantly increased with the increasing of dietary level of soya-saponins (p < 0.05), which was concomitant with the destroyed the intracellular junctions. In conclusion, the present work proved that soya-saponins induced enteritis and compromised the intestinal barrier functions. Based on the present work, strategies focus on regulation of cell apoptosis, epithelial permeability, intracellular junctions and redox homeostasis worth further investigating to develop new and efficient ways for SBMIE alleviation.

Dietary arginine supplementation mitigates the soybean meal induced enteropathy in juvenile turbot,Scophthalmus maximusL.

A 12-week feeding trial was conducted to investigate the protective effects of arginine on the intestinal health of juvenile turbot (Scophthalmus maximus L.) fed high doses of dietary soybean meal. Sextuple replicates of 30 fish were fed each of four isonitrogenous and isolipidic experimental diets: fish-meal-based diet (FM); FM with 40% fish meal protein replaced by soybean meal protein (SBM); SBM+1% arginine (ARG1) and SBM+2% arginine (ARG2). Turbot-fed SBM showed typical soybean meal-induced enteropathy, characterized by an increase in the thickness of lamina propria, as well as significant decreases in the absorptive surface and activities of intestinal brush border membrane enzymes and Na+, K+-ATPase. On the contrary, fish-fed ARG1 showed enhanced intestinal mucosal barrier function in terms of the enhanced gene expression of anti-inflammatory cytokine and barrier-forming tight junction proteins, as well as depressed gene expression of pro-inflammatory cytokines and pore-forming tight junction proteins. Fish-fed AGR2 showed intermediate intestinal performances between SBM and AGR1. Dietary arginine (1%) also significantly regulated the expression of AMP-activated protein kinase α1 (AMPKα1), myosin light chain kinase (MLCK) and nuclear transcription factor-κB p65 (NF-κB p65), and these regulations correlated well with its regulations on intestinal mucosal barrier related genes at all sampling time-points. In conclusion, arginine supplementation (1%) in diet for turbot mitigated the soybean meal-induced enteropathy by enhancing the intestinal mucosal barrier function. The activation of AMPKα1 signalling molecule as well as the suppression of NF-κB p65 and MLCK signalling molecules may mediate the beneficial effects of arginine.

Determination of optimal fasting time before blood sampling to get baseline data on serum biochemical characteristics in juvenile turbot (Scophthalmus maximus)

Serum biochemical characteristics provide crucial information about the physiological condition of fish and are greatly affected by the sampling conditions. This study examined the effects of short-term fasting periods [in terms of degree-days (°C days)] on the serum biochemical parameters of juvenile turbot (Scophthalmus maximus) and revealed the optimal fasting time before blood sampling to obtain the baseline data. Stomach content index (SCI), digestive somatic index (DSI), viscerosomatic index (VSI), hepatosomatic index (HSI), serum thyroid hormones (thyroxine, T4; triiodothyronine, T3), cortisol, glucose, lactate, cholesterol, triglyceride, high-density lipoprotein, low-density lipoprotein, total protein, albumin, globulin and albumin/globulin level of juvenile turbot were determined after different fasting durations (0, 0.25, 0.5, 1, 2 and 3 days). Results showed that the levels of SCI, T4, T3, cortisol, glucose, lactate, cholesterol, and triglycerides were significantly affected during fasting, whereas the levels of SCI, glucose, lactate, cholesterol, triglyceride were not significantly different at 1 (16.5 °C days), 2 (31 °C days), and 3 days (48 °C days) of fasting. Meanwhile, no significant difference was found for T4 and T3 at 1 day (16.5 °C days) and 2 days (31 °C days) of fasting, and for cortisol at 1 day (16.5 °C days) and 3 days (48 °C days) of fasting. However, DSI, VSI, HSI, high-density lipoprotein, low-density lipoprotein, total protein, albumin, globulin and albumin/globulin levels remained unchanged and showed no significant difference. These results indicate the importance of fasting period on the digestive system and serum biochemical properties of turbot. Therefore, based on these results and considering the fish management, 1 day (16.5 °C days) is the best fasting period prior to blood collection from juvenile turbot for blood biochemistry determination.

Apparent Digestibilities of Selected Feed Ingredients Fermented by Host Bacteria in Juvenile Turbot, Scophthalmus maxima L.

Fermentation is considered a promising method to improve the limited utilization of plant protein sources. In the present study, Shewanella sp. MR-7, isolated from the intestine of juvenile turbot, was used to ferment selected plant sources. We investigated the apparent digestibility coefficients (ADCs) of three plant sources fermented and not fermented by Shewanella sp. MR-7 in diets of juvenile turbot: soybean meal (SBM), fermented soybean meal (FSBM), peanut meal (PM), fermented peanut meal (FPM), corn gluten meal (CGM) and fermented corn gluten meal (FCGM). The ADCs of dry matter (DM), crude protein (CP), gross energy (GE), and amino acids（AA）were analyzed. Our results showed that the ADC of the plant protein sources improved significantly with fermentation. Moreover, the FSBM showed the highest improvement for apparent amino acid digestibility while FPM showed the lowest compared with the unfermented plant protein source. In conclusion, our results indicated that Shewanella sp. MR-7 fermentation can greatly improve the ADCs of SBM, PM, and CGM in diets of turbot. This study providedvaluable information for the use of host bacteria as zymocyte in aquaculture.

Transcriptomic Profiling of the Immune Response to Crowding Stress in Juvenile Turbot (Scophthalmus maximus)

In this study, juvenile turbot Scophthalmus maximus were vaccinated with attenuated Edwardsiella tarda (EIBAV1) and reared at two different densities, low density (LD), (5.25±0.02)kgm−2, as control group and high density (HD), (20.53±0.05) kg m−2, as experimental group. Only density was considered as the variable. Five weeks after vaccination, the transcriptomes of spleen and head kidney from the turbot in two groups were analyzed with RNA-Seq technology. A total of 447 million reads were assembled into 41136 genes with an average length of 1274 bp and a N50 size of 2295 bp. A comparison of gene expression between HD and LD groups revealed 1155 differentially expressed genes (DEGs). Enrichment and pathway analysis of the 10 immune-related DEGs showed the centrality of toll-like receptor signaling pathway, cytosolic DNA-sensing pathway and platelet activation in the host immune responses. The 5 overexpressed inflammatory cytokines and 5 downregulated signal-regulated cytokines genes are covered by these immune-related DEGs. It was inferred that cells suffer damage and the immune response is restrained in turbot under crowding stress.

Juvenile turbot (Scophthalmus maximus L., 1758) farmed in a modern low-water exchange RAS device: Growth performance using different diets and its commercial implications

ABSTRACTOne step to improve the economics of Recirculated Aquaculture Systems (RAS) is the use of the right feed. A 12-week lasting growth trial with juvenile turbot (Scophthalmus maximus) with an average initial weight of 54.4 ± 19.3 g evaluated the economic impact of choosing the best feed. Therefore, commercially available feeds recommended for turbot culture, two floating (feed 1 and feed 3) and one sinking (feed 2), were tested in a low-water exchange RAS device. Compositions of the macronutrients for the floating diets were 56.0% (protein), 12.0% (fat), 1.1% (fiber), and 10.0% (ash) for feed 1, which will be referred to as Floating 1, and 55.0% (protein), 16.0% (fat), 0.7% (fiber), and 11.0% (ash) for feed 3, which will be referred as Floating 2. The macronutrient composition of feed 2, which will be referred to as Sinking, was 50.0% (protein), 15.0% (fat), 1.4% (fiber), and 9.9% (ash). Growth performance differed significantly between feeds; the specific growth rates (SGR) ranged between 0.92% d−1 (Sinking) and 1.25% d−1 (Floating 1 and 2), resulting in a significantly higher growth rate for the floating feeds. Feed conversion ratios (FCR) were also significantly different, and Sinking showed the highest FCRs during the experiment. We assume that this was caused by the different swimming characteristics of the feeds and the foraging behavior of the fish instead of the different nutritional compositions of the diets. Including retailer prices, the feed costs per kg produced fish differed between 9.3% and 20.2%, resulting in the highest production costs for the Sinking. Therefore, finding the right feed for turbot and optimizing the feeding regime according to its requirements will improve the economic feasibility of turbot culture.

Dietary stachyose altered the intestinal microbiota profile and improved the intestinal mucosal barrier function of juvenile turbot, Scophthalmus maximus L.

Recent studies have revealed the beneficial effects of stachyose on intestinal histology and digestive function of fish. However, a comprehensive understanding of stachyose's impact on intestinal health of fish remains unclear, limiting its use in aqua-feed. In the present study, a 12-week feeding trial was conducted to investigate the effects of dietary stachyose on intestinal microbiota and mucosal barrier function of turbot (S. maximus L). Three isonitrogenous and isolipidic experimental diets were formulated to contain 0%, 1.25% and 5% stachyose, respectively. Sequencing of bacterial 16s rRNA V4 region indicated that dietary stachyose altered the intestinal adherent microbiota profile, which was supported by the diet-cluster of PCA, PCoA, beta diversity heatmap and phylogenetic tree. LEfSe and MetaStat analysis indicated that both 1.25% and 5% dietary stachyose significantly elevated the abundance of intestinal cellulose-degrading bacteria. However, the higher level of stachyose (5%) increased the abundance of intestinal beneficial bacteria as well as that of potential pathogenic bacteria. Moreover, 1.25% dietary stachyose significantly up-regulated the genes expression of occludin, claudin-3, and ZO-1, and down-regulated the gene expression of claudin-like in the intestine (P<0.05). Dietary stachyose at 5% significantly increased mucin-2 secretion and the gene expression of ZO-1, while significantly decreased the gene expression of claudin-like in the intestine (P<0.05). Collectively, our study showed that dietary stachyose supplementation could favorably modulate the profile of intestinal microbiota and enhance the intestinal mucosal barrier function in juvenile turbot. Stachyose showed promising potential of being used as prebiotic in diet for enhancing the intestinal health of turbot.

Exogenous enzymes supplementation enhances diet digestibility and digestive function and affects intestinal microbiota of turbot (Scophthalmus maximus) juveniles fed distillers' dried grains with solubles (DDGS) based diets

A trial was conducted to evaluate the effect of dietary exogenous enzymes supplementation on apparent digestibility of macronutrients, energy and amino acids, and on digestive enzymes activity and gut microbiota of turbot (Scophthalmus maximus) juveniles fed diets rich in plant feedstuffs. For that purpose, a control diet was formulated to contain circa half protein from fishmeal and the other half from plant feedstuffs (dried distillers' grains with solubles, soybean meal, corn gluten, and wheat gluten). Two other diets were formulated similar to the control but including exogenous enzyme complexes: Synergen® (Alltech; product of solid state fermentation of Aspergillus niger) or Natugrain®TS (BASF; non-starch polysaccharides degrading enzymes complex). Both exogenous enzyme complexes increased the apparent digestibility coefficient (ADC) of dry matter, while the ADC of protein, lipid, and energy were only increased with Natugrain®TS. Moreover, the ADC of methionine, isoleucine, and aspartic acid were increased with both exoenzymes supplementation, while the ADC of lysine and glycine were increased with Synergen® and the ADC of arginine and threonine were increased with Natugrain®TS. Dietary supplementation with Synergen® or Natugrain®TS did not affect intestinal pH but increased the activity of lipase and protease in the posterior intestine, while amilase activity was increased only with Natugrain®TS. Microbiota was also affected by both exoenzymes complexes, increasing its richness and diversity. Present results indicate that diet supplementation with exogenous enzymes complexes, Synergen® or Natugrain®TS, may be a feasible strategy to enhance the digestibility of plant feedstuff-rich diets for turbot juveniles.

Protective effect of glutamine and arginine against soybean meal-induced enteritis in the juvenile turbot (Scophthalmus maximus)

Soybean meal can induce enteritis in the distal intestine (DI) and decrease the immunity of several cultured fish species, including turbot Scophthalmus maximus. Glutamine and arginine supplementation have been used to improve immunity and intestinal morphology in fish. This study was conducted to investigate the effects of these two amino acids on the immunity and intestinal health of turbot suffering from soybean meal-induced enteritis. Turbots (initial weight 7.6 g) were fed one of three isonitrogenous and isolipidic diets for 8 weeks: SBM (control diet), with 40% soybean meal; GLN, SBM diet plus 1.5% glutamine; ARG, the SBM diet plus 1.5% arginine. Symptoms that are typical of soybean meal-induced enteritis, including swelling of the lamina propria and subepithelial mucosa and a strong infiltration of various inflammatory cells was observed in fish that fed the SBM diet. Glutamine and arginine supplementation significantly increased (1) the weight gain and feed efficiency ratio; (2) the height and vacuolization of villi and the integrity of microvilli in DI; (3) serum lysozyme activity, and the concentrations of C3, C4, and IgM. These two amino acids also significantly decreased the infiltration of leucocytes in the lamina propria and submucosa and the expression of inflammatory cytokines including il-8, tnf-α, and tgf-β. For the mucosal microbiota, arginine supplementation significantly increased microbiota community richness and diversity, and glutamine supplementation significantly increased the relative abundance of Lactobacillus and Bacillus. These results indicate that dietary glutamine and arginine improved the growth performance, feed utilization, and distal intestinal morphology, activated the innate and adaptive immune systems, changed the intestinal mucosal microbiota community, and relieved SBMIE possibly by suppression of the inflammation response.

The tolerance and safety assessment of taurine as additive in a marine carnivorous fish, Scophthalmus maximus L.

The effects of dietary taurine on growth performance, liver and intestine morphology, serum physiological and antioxidant parameters, serum thyroid hormone level, muscle taurine content and fatty acid composition of turbot were first evaluated, for the safe utilization in marine fish feed and for human food safety. Four experimental diets were formulated to contain 0, 10, 50 and 100 g/kg taurine. Each diet was randomly assigned to six replicates of 30 juvenile turbot (initial mean weight of 7.46 g). The feeding trial lasted for 10 weeks. The growth performance of fish was significantly enhanced by 10 g/kg dietary taurine. The integrity of the distal intestine was impaired and the absorptive surface was found to be significantly reduced by 100 g/kg dietary taurine. The obvious pathological changes in liver were observed in fish fed 100 g/kg taurine. Dietary taurine with 10 and 50 g/kg significantly increased the activities of serum superoxide dismutase, lysozyme and thyroid hormone. The taurine content in muscle was found to be significantly increased by dietary taurine; however, no significant differences were observed among taurine-supplemented treatments. This study suggested that 10 g/kg taurine was safe in turbot feed, and fivefold of safety margin was obtained.

Effect of dietary fatty acid composition on growth, fatty acids composition and hepatic lipid metabolism in juvenile turbot (Scophthalmus maximus L.) fed diets with required n3 LC-PUFAs

A 12-week feeding experiment was conducted to investigate the effects of dietary fatty acids composition on growth performance, lipid deposition and some genes expression of hepatic lipid metabolism in juvenile turbot (Scophthalmus maximus L.) (mean initial body weight, 9.49±0.03g) fed diets with required n3 LC-PUFA. Juvenile turbot were fed diets with palm oil (PO), rapeseed oil (RO), soybean oil (SO) or linseed oil (LO) replacing the same levels of fish oil (FO), respectively. Each diet was randomly fed to triplicate tanks, and each tank was stocked with 35 fish. The results showed that growth performance and feed utilization of turbot fed diets with required n3 LC-PUFA were independent of dietary fatty acids composition. As expected, C16:0, C18:1n, C18:2n-6, C18:3n-3 and n3 LC-PUFAs level in liver were up to the maximum in the PO, RO, SO, LO and FO group, respectively, and significantly higher than that in the other groups (P<0.05). Fish fed the diet with RO had the lowest plasma triglyceride and the highest HDL-c/LDL-c, although no significant difference of plasma triglyceride had been found between the RO group and the LO group. Hepatic lipid content in fish fed diets with SO, RO, and LO was significantly higher compared with PO and FO groups. The higher activities of hepatic G6PD and ME were found in fish fed diets with PO or FO compared to LO. The relative expression of LPL, LXR, and ApoB-100 gene in the RO group and the LO group, MTP gene in the LO group, PPARα and FAS genes in the PO group, and PPARγ gene in the SO group were significantly higher than those in the FO group. These results indicated that the increase in hepatic lipid deposition of turbot induced by the SO, RO, and LO diets are associated with up-regulation of some genes involved in lipids biosynthesis metabolism.

Dietary Zn and the subsequent organotropism in fish: No influence of food quality, frequency of feeding and environmental conditions (pH and temperature)

Trophic transfer of Zn in fish is affected by the type of food and environmental variables such as temperature. However, there is still a lack of knowledge regarding the effects of such factors on Zn organotropism. For this reason, a series of experimental studies have investigated how the distribution and the concentration of Zn is affected by some environmentally-relevant factors (food quality, food availability, water pH, and temperature) in turbot Scophthalmus maximus using radiotracer techniques. In three different experiments, Zn distribution in seven body compartments of juvenile turbot and the calculation of Zn concentration index (IC) for each compartment were compared. Its distribution as well as its concentration in the body compartments of juvenile turbots were not affected by the experimental conditions tested. This apparent consistency in the Zn organotropism can be explained by the ability of the fish to maintain Zn homeostasis at non-toxic Zn concentrations in their diet. These results are important to better understand the trophic transfer of Zn in fish under realistic environmental conditions.

Effects of dietary glycinin on the growth performance, digestion, intestinal morphology and bacterial community of juvenile turbot, Scophthalmus maximus L.

This study was run to investigate effects of dietary glycinin on the growth performance, digestion, intestinal morphology and bacterial community of juvenile turbot (Scophthalmus maximus L.). Graded levels (0%, 3%, 6% and 12%) of purified glycinin were added to the basal diet to formulate four experimental diets containing 0%, 2.18%, 4.17% and 8.31% immunologically active glycinin, respectively. Triplicate groups of 30 fish were fed to apparent satiation twice daily for 12weeks. Dietary inclusion of glycinin did not affect feed intake, feed efficiency ratio or weight gain of turbot, however, fish fed 12% glycinin showed a significant decrease in the apparent digestibility of dry matter and protein, as well as the whole-body lipid content. Meanwhile, slightly increased infiltration of mixed leukocytes in the lamina propria was observed in turbot fed 12% glycinin, so was specific IgM against glycinin in the serum. Sequencing of bacterial 16s rRNA V4 region showed that Proteobacteria (90.64%), Bacteroidetes (6.01%) and Firmicutes (1.73%) were the dominant bacteria in the intestine of turbot. Dietary inclusion of glycinin had no significant effect on the overall structure of bacterial community but dramatically reduced the relative abundance of the Vibrio genus, one of the core microbes, in a dose-independent manner. Our results suggest that turbot can tolerate a relatively high level of immunologically active glycinin (8.31%) in the diet without showing notable impairments of growth performance and gut function.

Interactive effect of ammonia and crowding stress on ion-regulation and expression of immune-related genes in juvenile turbot (Scophthalmus maximus)

The present study was to investigate the interactive effect of ammonia and crowding stress on ion-regulation and expression of immune-related genes in juvenile turbot (Scophthalmus maximus). The fish were exposed to four total ammonia nitrogen (0, 5, 20, 40 mg/L TAN) and two stocking density. After 96 h of exposure, blood, gill, and liver samples were collected to measure biochemical parameters and mRNA levels of immune-related genes. The results showed that co-exposure to high TAN (20 and 40 mg/L) and high density significantly increased plasma sodium (Na+), gill Na+/K+-ATPase activity and mRNA levels. Following individual and combined exposure to high TAN and high density, the heat shock protein 70 (HSP 70), HSP 90, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) genes expression were obviously higher than their control. Conversely, the lysozyme (LZM) and hepcidin mRNA levels were down-regulated in liver of fish exposed to high TAN alone and combination of high TAN-density. Moreover, glutathione S-transferase (GST) mRNA levels significantly increased in treatments with individual high TAN and high density, but decreased in high TAN-density co-exposed fish. Overall, ion homeostasis and immune status were adversely influenced in high exposed turbot under high density.

Investigations of temperature and pH variations on metal trophic transfer in turbot (Scophthalmus maximus).

Studying dietary metal transfer kinetics is essential to gain a better understanding in global metal accumulation rates and its impacts in marine fish. While there exists a solid understanding on the influence of various biotic factors on this transfer, metal assimilation in fish might be also affected by abiotic factors, as has been observed in marine invertebrates. The present study therefore aims to understand the potential effects of two climate-related master variables, temperature and pH, on the assimilation efficiency (AE) of essential (Co and Zn) and non-essential (Ag) metals in the turbot Scophthalmus maximus using radiotracer tools. Juvenile turbots were acclimated for 8weeks at two temperatures (17 and 20°C) and pH (7.5 and 8.0) regimes, under controlled laboratory conditions, and then fed with radiolabelled shrimp (57Co, 65Zn and 110mAg). Assimilation efficiencies of Co and Ag in juvenile turbot, determined after a 21-day depuration period, were not affected by pre-exposition to the different environmental conditions. In contrast, temperature did significantly influence Zn AE (p<0.05), while pH variations did not affect the assimilation of any of the metals studied. In fact, temperature is known to affect gut physiology, specifically the membrane properties of anterior intestine cells where Zn is adsorbed and assimilated from the ingested food. These results are relevant to accurately assess the influence of abiotic factors in AEs of metals in fish as they are highly element-dependent and also modulated by metabolic processes.

Effects of replacing fishmeal with different cottonseed meals on growth, feed utilization, haematological indexes, intestinal and liver morphology of juvenile turbot (Scophthalmus maximusL.)

A ten-week feeding trial was conducted to evaluate the effect of replacing fishmeal with two differently processed cottonseed meals (CSM), namely XC and SC, separately in turbot (5.28 ± 0.02 g). Nine isonitrogenous and isoenergetic diets were formulated without fishmeal replacement (FM), 150 g/kg (XC15, SC15), 250 g/kg (XC25, SC25), 350 g/kg (XC35, SC35) and 450 g/kg (XC45, SC45) of fishmeal replaced by CSM. Fishmeal was successfully replaced by XC in turbot diets without growth reduction at 350 g/kg, but not by SC even at 150 g/kg. The apparent digestibility coefficients of SC-included diets were significantly lower than XC-included diets at same replacement level. The activities of aspartate aminotransferase and superoxide dismutase were significantly affected in XC45 and SC45 group. The XC45 and SC-included diets caused shortened distal intestine villi height and structural damage of liver compared with FM diet. This study indicated that different processing methods could affect the nutritional value of CSM and effect as a protein source for turbot. CSM with high quality could be an important alternative dietary protein source for juvenile turbot.

Effect of fish meal replacement by plant protein blend on amino acid concentration, transportation and metabolism in juvenile turbot (Scophthalmus maximusL.)

The objective of the study was to evaluate the effects of incorporating plant protein blend in juvenile turbot (Scophthalmus maximus L.) diet on free amino acid (AA) concentration and the expression of genes related to peptide and AA transporters, key enzymes of AA metabolism and AA response (AAR) pathway. Fish were fed diets with fish meal (FM), or 400 g/kg FM replacement by plant protein blend for 9 weeks. Compared with the FM diet, PP40 diet did not affect plasma essential amino acid (EAA) concentration or AA metabolic enzymes gene in intestine, while it significantly upregulated all the detected peptide and neutral AA transporters gene. Results in muscle indicated that PP40 diet led to a great reduction of EAA concentrations and mRNA abundance of two kinds of AA transporters (SNAT2 and b0,+AT), while it greatly increased the gene expression of L-type and T-type AA transporters (LAT2 and TAT1) and the enzymes of AA catabolism (BCKDH-E2) and anabolism (asparagine synthetase). In addition, the expression of genes related to AAR pathway were all greatly stimulated by PP40 diet in muscle. Our results provide a molecular explanation for the change of tissues AA concentrations caused by plant protein in turbot, which maybe applicable for general carnivorous fish.

Effects of Feeding Frequency and Ration Level on Growth Performance and Non-Specific Immunity of Juvenile Turbot (Scophthalmus maximus) at Different Growth Stages

Four growth trials were carried out to optimize a feeding regime for turbot in industrial aquaculture systems at 15±0.5°C. Six ration levels (50%, 60%, 70%, 80%, 90%, and 100%) of satiation were tested in trial I and five ration levels (60%, 70%, 80%, 90% and 100%) of satiation were tested in trial III. For optimal feeding frequency, turbot were fed to satiation for 1 meal/day, 2 meals/day, 3 meals/day in trial II, and 1 meal every other day, 1 meal/day, and 2 meals/day in trial IV. The average initial body weight of fish was 28.90±0.07g for trials I &amp; II, and 181.75±1.05g for trials III &amp; IV. Growth performance generally decreased and feed utilization increased with decreasing ration levels, while no significant differences were observed with small sized turbot fed to 80%, 90%, 100% levels of satiation, and with large sized turbot fed to 90% &amp; 100% levels of satiation. There was no increase in size heterogeneity with decreasing ration levels. Ration levels significantly influenced water quality. There were no significant differences in growth and feed efficiency among turbot fed with different feeding frequencies. Feeding small size turbot once a day and large size turbot once every other day at a ration level of 80% satiation is suggested for better feed utilization and less waste output.