Effect of growth hormone transgenic Synechocystis on growth, feed efficiency, muscle composition, haematology and histology of turbot (Scophthalmus maximus L.)

The present study investigated the effect of supplementing feed with transgenic Synechocystis sp. PCC6803 containing the Paralichthys olivaceus growth hormone (GH) gene on growth, feed intake and feed efficiency ratio, muscle composition, haematology and histology of turbot (Scophthalmus maximus L.). At the end of the 40‐day feeding trial, the specific growth rate of fish fed the supplemented feed with 1.0% transgenic Synechocystis sp. PCC6803 was 21.67% higher (P<0.05) than that of control fish. Although body weight and feed efficiency ratio significantly increased (P<0.05) in fish fed the diet supplemented with transgenic alga, feed intake and condition factor of the experimental fish were unaffected. Muscle composition analysis showed that the protein content was positively influenced by the transgenic alga, whereas the lipid content was unaffected. Haematological parameters, including red blood cell, white blood cell, haemoglobin, and serum biochemical indices, such as enzyme activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, concentrations of total protein, glucose, blood urea nitrogen, creatinine, triglyceride and cholesterol and ion levels of K, Na, Cl, P were not influenced by supplementing the transgenic Synechocystis sp. PCC6803. Furthermore, no histopathological alterations were induced by transgenic alga treatment in the stomach, intestine, liver, spleen and kidney of the experimental fish. The results of the present study indicated that transgenic Synechocystis sp. PCC6803 containing P. olivaceus GH gene is an efficient growth promoter and a safe feed additive for fish.     

Experimental infection of turbot, Scophthalmus maximus (L.), by Moritella viscosa, vaccination effort and vaccine-induced side-effects

Moritella viscosa is the causative agent of winter ulcers in farmed salmonids and Atlantic cod in countries around the North Atlantic. The bacterium has also been isolated from various marine fish species. Bacterial diseases have been a limiting factor in farming of turbot, but M. viscosa has not so far been isolated. In this study, turbot was shown to be sensitive to M. viscosa infection in experimental challenges. Pathological changes in infected turbot were comparable with those previously described for winter ulcers in salmon. A multivalent commercial salmon vaccine, containing M. viscosa as one of five antigens and a mineral oil adjuvant, did not protect turbot against challenge 13 weeks post-vaccination. Weight gain of vaccinated turbot compared with controls was not reduced 7 weeks post-vaccination. Vaccination did not induce a specific anti-M. viscosa response, while elevated anti-M. viscosa antibody levels were detected both in vaccinated and unvaccinated fish 5 weeks post-challenge. The vaccine did, however, induce an antibody response against Aeromonas salmonicida, another vaccine component. Minor intra-abdominal adhesions were detected in vaccinated fish and fish injected with a mineral oil adjuvant. The measurement of various innate humoral immune parameters did not reveal significant differences between vaccinated and control groups.     

Experimental infection of turbot, Scophthalmus maximus (L.), by Aeromonas salmonicida subsp. achromogenes and evaluation of cross protection induced by a furunculosis vaccine

Turbot was shown to be sensitive to injection challenges by Aeromonas salmonicida subsp. achromogenes (Asa). A systemic disease was induced and the bacterium was isolated from various internal organs. Histopathological changes involved haemorrhages, necrosis and degeneration in skin and muscle, haemorrhages and necrosis in kidney, degeneration in the heart muscle, and fusion of the secondary gill lamellae. A polyvalent commercial salmon vaccine, containing A. salmonicida subsp. salmonicida as one of five antigens, did not confer protection in turbot against an experimental Asa infection 13 weeks post-vaccination. Vaccination induced a significant antibody response against Asa cells but not against extracellular products of the bacterium. The results of the study indicate that Asa may be a potential threat to turbot farming and that the development of new turbot vaccines is needed.     

Effects of different dietary arachidonic acid : docosahexaenoic acid ratios on phospholipid fatty acid compositions and prostaglandin production in juvenile turbot (Scophthalmus maximus)

Five purified diets containing AA (20:4n-6) at 0.02–0.78% dry weight and DHA (22:6n-3) at 0.93–0.17% dry weight were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 0.87 g for a period of 11 weeks. The dietary DHA:AA ratio ranged from 62 to 0.2. Incorporation of AA into liver phospholipids increased with increasing dietary AA input. Phospholipids from fish fed diets containing 0.02, 0.06 and 0.11% of dry weight as AA generally contained less AA compared to fish fed fish oil while those fed diets containing 0.35 and 0.78% of dry weight as AA had higher AA levels in their phospholipids. The highest levels of AA were found in PI but the greatest percentage increase in AA incorporation was in PE and PC. Brain phospholipid fatty acid compositions were less altered by dietary treatment than those of liver but DHA content of PC and PE in brain was substantially lower in fish fed 0.93% pure DHA compared to those fed fish oil. This suggests that dietary DHA must exceed 1% of dry weight to satisfy the requirements of the developing neural system in juvenile turbot. In both tissues, (20:5n-3) concentration was inversely related to both dietary and tissue PI AA concentration. Similar dietary induced changes in AA, EPA and DHA concentrations occurred in the phospholipids of heart, gill and kidney. PGE₂ and 6-ketoPGF₁ were measured in homogenates of heart, brain, gill and kidney. In general, fish fed the lowest dietary AA levels had reduced levels of prostaglandins in their tissue homogenates while those fed the highest level of AA had increased prostaglandin levels, compared to fish fed fish oil. In brains, the PGE₂ concentration was only significantly increased in fish fed the highest dietary AA.Abbreviations AA arachidonic acid - DHA docosahexaenoic acid - EFA essential fatty acid - EPA eicosapentaenoic acid - HPTLC high performance thin-layer chromatography - HUFA highly unsaturated fatty acid - PC phosphatidylcholine - PE phosphatidylethanolamine - PGE prostaglandin E - PGE prostaglandin E - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acid - TLC thin-layer chromatography     

Larval growth of turbot, Scophthalmus maximus (L.) produced with fresh and cryopreserved sperm

The present paper assesses the fertilization and hatching rates, as well as the growth, of larvae obtained from four artificial fertilizations (AF) using fresh and cryopreserved sperm of the turbot Scophthalmus maximus (L.). Larvae growth in both sperm groups, measured in terms of length and weight at culture days 0, 7, 14 and 31, are compared, as well as their growth rates. The two groups' fertilization and hatching rates were not significantly different. Likewise, no significant differences in length and wet weight of 7‐ and 14‐day‐old larvae were found using fresh and cryopreserved sperm; however, significant differences were found in 31‐day‐old larvae, which were more attributable to the variability inherent in larval turbot culture, and to variability in the reproductive specimens used in our study, than to the type of sperm employed. These results indicate that the type of sperm used in artificial fertilization, i.e. fresh or cryopreserved, is not a determining factor, either for fertilization and hatching, or for subsequent larval development. Our results also confirm once again the high quality of cryopreserved turbot sperm, and its usefulness in commercial hatcheries.     

大菱鲆胚胎玻璃化方法研究

用大菱鲆(Scophthalmus maximus)神经期胚对6种抗冻剂的毒性进行检测,发现其毒性排列为1,2-丙二醇(PG)<甲醇(MeOH)<甘油(Gly)<二甲基甲酰胺(DMF)<乙二醇(EG)<二甲亚砜(DMSO).以DMF为主因子配制和筛选出11种玻璃化程度较好的玻璃化液,并用大菱鲆肌节期胚对其中5种玻璃化程度最好的玻璃化液进行检测,结果显示,A4(DMSO 20%+DMF 25%)、A7(DMSO 25%+DMF 20%)较适合于大菱鲆胚胎的平衡处理,利用A4和A7平衡处理神经期胚、肌节期胚、心跳期胚、出膜前期胚,结果显示大菱鲆神经胚和肌节胚对玻璃化液的适应能力较强.实验测试出不同时期胚胎在两种玻璃化液中的成活率,为大菱鲆各期胚胎在玻璃化液中的平衡处理提供了依据.利用大菱鲆肌节胚对不同的平衡步骤进行了筛选,发现五步法的平衡效果较好.     

The effect of dietary vitamin E and C level on market-size turbot (Scophthalmus maximus) fillet quality

Fish fillet quality has been shown to be influenced by the level of antioxidants in preslaughter diet. Thus, an experiment was conducted to study the effect of different levels of vitamin E and C on the fillet quality of market‐size reared turbot (Scophthalmus maximus). Turbot of a mean initial weight of 347 ± 20 g were divided into four groups and fed commercial turbot diets (60% protein, 12% fat), supplemented with α‐tocopheryl acetate (mg kg^?1) and ascorbyl‐2 monophosphate (mg kg^?1) at the following dietary levels: 500/100, 1000/100, 100/1000, 100/100 respectively. Over a dietary supplementation period of 15 weeks, fish were fed to satiation and reached a final mean weight of 916 ± 29 g. α‐Tocopherol levels increased significantly (P < 0.001) in tissue (i.e. muscle, liver, heart and kidney) of fish fed diets containing elevated levels of α‐tocopheryl acetate. In ice storage, fillets of these fish exhibited significantly lower (P < 0.001) levels of lipid oxidation, and showed significantly less (P < 0.001) colour deterioration (higher hue angle and lower chroma). Elevated dietary α‐tocopheryl acetate levels had a negative effect (P ≤ 0.001) on the concentration of ascorbic acid in muscle tissue. An increase in dietary vitamin C did not have any detectable effect on fillet quality. Prolonged feeding times had a negative effect on lipid oxidation (P < 0.001) and colour deterioration (P < 0.01). These results suggest that increased dietary α‐tocopheryl acetate could prevent colour deterioration and lipid oxidation of turbot fillets in retail storage on ice.     

Stress responses of larval turbot, Scophthalmus maximus L., exposed to sub-lethal concentrations of petroleum hydrocarbons

Turbot larvae were exposed to dilutions of the water soluble fraction (WSF) of crude oil (1–25%), in a laboratory flow-through system. Whole body immunoreactive cortisol (IRC) content of premetamorphic 345 degree C day and early metamorphosing 450 degree C day larvae (23 and 30 days post hatch, respectively) was elevated when exposed to 25% WSF for 6 h, but the lower WSF concentrations did not induce IRC elevations. Larvae of 450 degree C days exposed to WSF for 6 h and then left in clean sea water for 24 h showed recovery of IRC, whilst the IRC content of 450 degree C day larvae exposed to WSF for 30 h remained elevated. Whole body thyroxine content of 345 degree C day larvae exposed to 25% WSF for 6 h was significantly elevated, which may have implications for larval development/metamorphosis. However, whole body triiodothyronine content of these larvae was not altered by WSF-exposure. Furthermore, larvae of 450 degree C days, WSF-exposed for 6 h or 30 h showed no thyroidal disturbance. Larvae of 345 degree C days exhibited significantly elevated whole body adrenaline and noradrenaline content after exposure for 6 h to 25% WSF; however, more diluted WSF did not influence adrenaline or noradrenaline content. These studies have demonstrated that larvae of 345 and 450 degree C days can successfully mount endocrine stress responses but that environmentally realistic concentrations of petroleum hydrocarbons do not induce these responses.     

Lipid digestion in turbot (Scopthalmus maximus) 11: Lipolysis in vitro of 14C-labelled triacylglycerol,cholesterol ester and phosphatidylcholine by digesta from different segments of the digestive tract

Preparations of digesta from the stomach, foregut, hindgut and rectum of turbot (Scophthalmus maximus) were assayed for the ability to hydrolyse glycerol tri[1-¹⁴C]oleate (¹⁴C-TAG), 1,2-di[1-¹⁴C]palmitoyl L-3-phosphatidylcholine (¹⁴C-PC) and cholesterol [1-¹⁴]oleate (¹⁴C-CE) over 1,2,3 and 17h. In the assay of foregut digesta with ¹⁴C-TAG substrate, 37.8% of the total radioactivity was found in the FFA class after the first hour of incubation. This value increased to a maximum of 68.5% of the available label after 17h incubation. Over the same time the proportion of radioactivity in diacylglycerols (DAG, 31.6%–7.4%) decreased while that in the monoacylglycerols increased (MAG, 14.0%–22.3%). In assays of digesta from the hindgut and rectum, after 1 h of incubation, the proportion of radioactivity recovered in FFA represented 64.9% and 74.8%, respectively, whereas the proportions in both DAG and MAG decreased with incubation time. Similarly to ¹⁴C-TAG, the highest rate of lipolytic hydrolysis of ¹⁴C-CE occurred in digesta from the posterior digestive tract where the proportions of radioactivity recovered in FFA of the hindgut (50.0%) and rectum (81.9%) preparations were substantially higher than those of the stomach (3.5%) and the foregut (14.4%) after 1h. With ¹⁴C-PC as substrate the levels of radiolabelled FFA in both the foregut and the hindgut (2.4% and 7.6%, respectively) were markedly lower than the 37.5% in the rectum. The results suggest that the posterior digestive tract is very active in non-specific and phospholipid lipolysis and a region where the major part of lipid digestion takes place.     

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

One 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.