Evaluating the most suitable nonlinear growth model for turbot (Scophthalmus maximus) in aquaculture 2 (weight application): Multi‐criteria model selection and growth prediction

Seeking the most suitable model to describe the growth of turbot, we analysed growth data of two different turbot (Scophthalmus maximus) strains reared communally in a recirculating aquaculture system. We fitted 10 different nonlinear growth models to individual weight gain data (n = 2,010) during the grow‐out phase. Analyses were carried out for each strain, for sexes within strains and for a pooled data set containing both strains and sexes. To assess the model performance, three different criteria are used. Further, a growth‐simulation was performed to evaluate the shape of the generated curve. This way we could assess the capability of the models to predict future growth. The 3‐parametric Gompertz model achieved the best fit in 42.9% of all cases tested and the lowest Bayesian information criterion in 100% of cases. The model produced realistically shaped curves and asymptotic values matching the biological attributes of the species. In contrast, 5‐parametric functions projected unrealistically shaped curves and predicted improbable mature sizes. Our results show that increasing number of parameters do not lead to increasing goodness of fit, but tend to result in overfitting, and demonstrate the advantages of the 3‐parametric Gompertz model for describing the growth of turbot.     

Analysing the growth of turbot (<Emphasis Type="Italic">Psetta maxima</Emphasis>) in a commercial recirculation system with the use of three different growth models

The growth data of a commercial aquaculture recirculation system were analysed to investigate the growth performance of reared turbot (Psetta maxima). Three common growth models (von Bertalanffy, Gompertz and Schnute) were fitted to the growth data documented over a time period of 6 years. To determine the most suitable model, three different criteria were used: (1) the Akaike index criterion, (2) the sum of squared residuals and (3) the average daily deviation between the estimated final weight and the observed final weight. The evaluation of the growth models showed that the Schnute model had the lowest Akaike index, the lowest sum of squared residuals and the lowest daily deviation between estimated and real weight of all tested growth models. The Schnute model produced sigmoid growth curves. The estimated growth coefficients were the most realistic ones in regard to biological interpretation. In contrast, the von Bertalanffy growth model and the Gompertz model estimated inaccurate exponential growth curves and are therefore unable to simulate the growth data as well as the Schnute model. The results indicate that the von Bertalanffy growth model is not the optimal model to simulate the present growth data and that the growth potential of reared turbot has probably not yet been fully exploited in the aquaculture system(s) examined (so far).     

A production season of turbot larvae Scophthalmus maximus (Linnaeus, 1758) reared on copepods in a Danish (56°N) semi‐intensive outdoor system

Turbot were reared from yolk sack larvae to juvenile in an outdoor semi‐intensive system. Three production cycles were monitored from May to September. A pelagic food chain was established with phytoplankton, copepods and turbot larvae. Abiotic and biotic parameters of lower trophic levels together with turbot larval survival, development, prey electivity and growth were monitored. A decreasing larval survival from 18.4% in May to 13.6% in July and just 7.0% in September was observed. The overall phytoplankton and copepod abundance decreased during the productive season. The turbot larval growth showed significant differences between larvae below (isometric) and above (allometric) 7 mm. Larval fish gut content showed no differences with available prey between production cycles. Therefore, it appears that the available prey concentration is governing their growth in this outdoor system. First‐feeding turbot larvae exhibited active selection for nauplii whereas developed larvae switched to copepodites and adult copepods. Although developing turbot larva exhibited active selection towards copepod size classes, there was no evidence of selective feeding on either of the two dominant copepod species. The turbot larvae's prey ingestion was modelled together with the standing stock of copepod biomass. The model results indicated that the estimated need for daily ingestion exceeded the standing stock of copepods. Hence, the initially established food web was unable to sustain the added turbot larvae with starvation as a consequence. We therefore suggest several solutions to circumvent starvation in the semi‐intensive system.     

Growth and survival of young turbot (Scophthalmus maximus L.) produced with cryopreserved sperm

This study assessed the growth and survival over a year of two groups of 4‐month‐old turbot Scophthalmus maximus (L.) derived from artificial fertilization with fresh (FG) and cryopreserved sperm (CG). Growth in both groups, measured monthly in terms of length and weight, were compared. Survival was also recorded. No significant differences were found when we compared weight and length data in both groups. Growth rates were similar between FG and CG young turbot during 1 year. Likewise, the same survival rate (92.2%) was found in both groups. Our results show the good survival and growth of young turbot obtained from cryopreserved sperm, and confirm the cryopreservation technique as a useful tool for raising turbot for commercial purposes.     

Blue mussel meal as feed attractant in rapeseed protein‐based diets for turbot (Psetta maxima L.)

Antinutritional factors in rapeseed products have been identified to reduce feed palatability and growth performance of turbot. Therefore, we evaluated the potential of blue mussel (Mytilus edulis L.) meal as feed attractant in rapeseed protein‐based diets for turbot. Triplicate fish groups received isonitrogenous and isocaloric diets with fish meal (FM) protein replacements of 50% or 75% by rapeseed protein concentrate (RPC 50, RPC 75). These diets were supplemented with 0%, 2%, 4% or 8% of blue mussel meal. In contrast with RPC 50 diets, fish fed with RPC 75/0 showed significantly reduced daily feed intake (DFI) and specific growth rate (SGR). With increasing mussel meal inclusion, RPC 75 diets resulted in increased DFI and SGR, suggesting mussel meal as attractant in rapeseed protein‐based diets for turbot. Feed conversion was unaffected by any treatment. Protein productive value and apparent digestibility coefficients were unaffected by either RPC or mussel meal inclusion. With regard to the whole body composition, no differences in crude protein, crude lipid and ash content could be determined. Haematological characteristics were unaffected among the treatments indicating good nourished and unstressed fish. In conclusion, we demonstrated that the utilization of blue mussel meal improved the palatability of rapeseed protein‐based diets for turbot.     

Protection of turbot, Scophthalmus maximus (L.), and rainbow trout, Oncorhynchus mykiss (Richardson), against vibriosis using two different vaccines

Abstact. The potency of a whole-cell bacterin (WCB) and a toxoid enriched whole-cell vaccine (WCEB) administered intraperitoncally into rainbow trout, Oncorhynchus mykiss (Richardson), were compared. The most effective vaccine was further evaluated by bathing turbot, Scophthalmus maximus (L.). These vaccines were composed of three strains of V. anguillarun , of the serotypes 01 and 02. Both vaccines conferred the highest protection against strains of serotype 01 within 4 weeks. With the toxoid enriched vaccine giving the best results (77 RPS). When trout were revaccinated after 7 weeks with this vaccine, good protection was achieved against strains of serotypes 01 and 02. Interestingly, when the WCEB was administered by bath to turbot, acceptable levels of protection against strains of both serotypes were obtained after 4 weeks of immunization.     

Effect of size‐fractionated fish protein hydrolysate on growth and feed utilization of turbot (Scophthalmus maximus L.)

Four experimental diets were fed to turbot to examine the effect of fish hydrolysate and ultra‐filtered fish hydrolysate on growth performance, feed utilization and non‐specific immune response. Fish hydrolysate was produced by enzymatic treatment and size fractionated using ultra‐filtration (UF). The permeate (molecular weight <1000 Da) after UF and the non‐ultra‐filtered fish hydrolysate (NUF) were tested as feed ingredients. Diets UF1, UF2 contained 3.7%, 1.2% ultra‐filtered fish hydrolysate to replace fish meal protein respectively. The diets UF1, NUF were identical in composition except that the molecular weight of fish hydrolysate in the diet. Fish meal was used in the control diet. All diets were made equal in protein, lipid and energy. Each experimental diet was fed to juvenile turbot (27.87 ± 0.04 g) in triplicate for 8 weeks. Results of this study indicate that the best overall growth and feed utilization of turbot juveniles were obtained with a diet containing higher dose of the small molecular weight compounds in fish hydrolysate. Acid phosphatase, alkaline phosphatase, lysozyme and superoxide dismutase activity in serum were not affected by diet. Total antioxidant capacity was improved with increasing level of low molecule weight fish hydrolysate (UF1).     

Effect of temperature on growth,digestion and immunity of green,white and purple sea cucumbers,Apostichopus japonicus (Selenka)

Three color morphs (white, green and purple strains) of Apostichopus japonicus (Selenka) were cultured in artificial seawater, for approximately 90 days, in three temperature ranges: 27–22°C (high), 22–17°C (mid) and 17–12°C (low). All strains grew in all temperature ranges. Temperature significantly affected growth rate, digestibility, digestive enzymes and immune‐related enzymes. Highest specific growth rates were exhibited in 4‐month‐old sea cucumbers at mid and high temperatures, and in 16‐month‐old sea cucumbers at mid and low temperatures. Specific growth rates of green and purple strains were not significantly different, but were significantly higher than that of the white strain at mid temperatures. The digestibility of each strain was significantly higher at 27°C, 22°C and 17°C than at 12°C. Green‐strain digestibility was higher than that of purple and white strains at specific temperatures. Protease and amylase activities of all strains followed bell‐shaped temperature curves with maximum digestive enzyme activity at 17°C. The activities of alkaline and acid phosphatases were higher in the guts of the green strain than in the white or purple strains at the same temperature. Superoxide dismutase activity was higher in the purple strain than in white and green strains.     

Dietary soya allergen β‐conglycinin induces intestinal inflammatory reactions,serum‐specific antibody response and growth reduction in a carnivorous fish species,turbot Scophthalmus maximus L.

This study was conducted to investigate the effects of dietary β‐conglycinin on the growth performance, digestion, gut morphology and immune responses of juvenile turbot (Scophthalmus maximus L.). Four diets were formulated to contain 0%, 2%, 4% and 8% purified β‐conglycinin. Triplicate groups of 30 fish were fed to apparent satiation twice daily for 12 weeks. Fish fed 4% and 8% dietary β‐conglycinin showed significantly reduced specific growth rate, feed efficiency ratio, apparent digestibility coefficient of nutrients and whole‐body lipid contents, as well as a profound infiltration of mixed leucocytes in the lamina propria and a significant decrease in the absorptive surface of distal intestine. The expression of pro‐inflammatory cytokines, TNF‐α and IL‐1β, in the distal intestine was significantly upregulated by 4% dietary β‐conglycinin, whereas a significantly lower expression level of IgM and anti‐inflammatory cytokine TGF‐β1 was observed in fish fed 8% dietary β‐conglycinin. Serum lysozyme and alternative complement pathway activity were first significantly enhanced by 2% dietary β‐conglycinin and then rapidly declined by 4% and 8% dietary β‐conglycinin. Respiratory burst activity of head kidney macrophages and serum superoxide dismutase activity were significantly suppressed by 4% and 8% dietary β‐conglycinin. Dietary β‐conglycinin (2–8%) significantly increased the level of specific antibody against β‐conglycinin in serum. Collectively, these results suggested that higher levels of dietary β‐conglycinin (4–8%) induced a variety of non‐specific and specific immune responses and intestinal mucosal lesions in turbot, resulting in inferior feed utilization and poor growth performance.     

Effects of ammonia exposure on stress and immune response in juvenile turbot (Scophthalmus maximus)

The aim of this study was to investigate the effects of ammonia exposure on stress and immune response in turbot. The species was exposed to five total ammonia nitrogen (TAN) concentrations: 0 (control), 1, 5, 20 and 40 mg L^?1 for 96 h. After 0, 24, 48 and 96 h of exposure, blood samples were collected to measure the levels of corticotropin‐releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, growth hormone (GH), lysozyme (LZM), complement 3 (C3), complement 4 (C4) and immunoglobulinM (IgM); liver samples were taken to analyse oxidative stress parameters (superoxide dismutase, SOD; catalase, CAT; glutathione, GSH; malondialdehyde, MDA), and gene expression of heat shock proteins (HSP 70 and HSP 90) and insulin‐like growth factor‐1 (IGF‐1). The results showed that exposure to higher concentrations of TAN (20 and/or 40 mg L^?1) enhanced the levels of CRH, ACTH and cortisol and attenuated the levels of GH, LZM, C3, C4 and IgM in plasma of turbot after 48 and 96 h. In liver, TAN (20 and/or 40 mg L^?1) apparently increased the activities of antioxidative enzymes (SOD and CAT), mRNA levels of HSP (HSP 70 and 90) and formation of MDA, decreased the content of GSH and mRNA levels of IGF‐1 after 48 and 96 h of exposure. Overall, our results suggested that high ammonia exposure caused activation of hypothalamic–pituitary–interrenal axis, inhibition of GH/IGF axis and immunity, and occurrence of oxidative stress.     

Reproduction, gamete supply and larval rearing of New Zealand turbot Colistium nudipinnis (Waite 1910) and brill Colistium guntheri (Hutton 1873): a potential new aquaculture species

New Zealand turbot Colistium nudipinnis (Waite 1910) and brill Colistium guntheri (Hutton 1873) were studied to assess their potential for aquaculture development. The reproductive cycle of wild fish showed a long spawning season from winter to summer, during which it is possible to obtain gametes. Both species have a diurnal ovulatory cycle, and gamete collection, by stripping and fertilizing at sea, was most successful within 2–3 h before and after sunset. Male reproductive anatomy suggests that these flatfish spawn in close proximity and that pair formation is highly likely. The eggs of both species have multiple oil droplets, turbot eggs being slightly larger (0.99 mm diameter) with more droplets (18–55) than brill eggs (0.97 mm, 13–26 droplets). Hatching occurred approximately 84 h after fertilization at 14 °C. Newly hatched turbot averaged 2.2 mm in length, and brill averaged 2.1 mm. First feeding began 4 days post-hatch (DPH). During larval rearing, rotifers were replaced by Artemia nauplii at 10 DPH. Metamorphosis commenced at 12–15 DPH and was completed and the larvae settled by 45 DPH. Weaning to inert foods began at 20–22 DPH (50 mg weight) and was completed by 57 DPH. Survival of turbot was 22.8% from fertilized egg to hatching, 7.3% through incubation to 22 DPH and 2.1% through incubation to fully weaned juveniles. Weaning success for turbot from metamorphosis to 57 DPH was 31.5%.     

Fishmeal replacement by mixed plant proteins and maggot meal on growth performance,target of rapamycin signalling and metabolism in juvenile turbot (Scophthalmus maximus L.)

Fishmeal could only be replaced by plant proteins at limited levels in aquafeeds, especially for carnivorous fish. In this study, an experiment was designed to evaluate the possibility of improving the utilization of plant proteins by maggot meal supplementation in turbot diet. Five diets were formulated: a reference diet (FM) containing 63% fishmeal and four experimental diets (35(0%), 35(3%), 40(0%), 40(3%)) in which fishmeal was substituted at different levels by plant proteins with 0–3% maggot meal. Turbot (4.90 ± 0.03 g) was fed with these diets for 9 weeks. Fishmeal was successfully replaced by plant proteins in turbot diet without growth reduction at 35% but not 40%. However, maggot supplementation (3%) at 40% plant protein replacement level achieved comparable growth performance with that of fishmeal. Maggot meal supplementation improved apparent digestibility coefficients, plasma hydroxyproline levels, intestine trypsin activities and activated target of rapamycin (TOR) signalling, all of which were decreased or down‐regulated after high plant protein replacement. Therefore, this study demonstrated maggot meal, a potential valuable protein source for turbot.     

Characterization of Edwardsiella tarda strains isolated from turbot, Psetta maxima (L.)

The biochemical, serological and molecular characteristics of a group of 21 Edwardsiella tarda strains isolated from turbot, Psetta maxima, in two different areas of Europe were analysed and compared with a total of 13 strains of this bacterial species with different geographical and host origins. All the turbot isolates were biochemically identical to the E. tarda strains included as reference. The use of different techniques including microagglutination, dot blot and Western blot of lipopolysaccharides allowed us to determine that all the turbot isolates constitute an homogeneous and distinctive serological group. Genetic analysis by randomly amplified polymorphic DNA (RAPD) analysis demonstrated that although the E. tarda strains from turbot were compiled in a unique group using the primers P3 and P6, two clonal lineages could be detected when oligonucleotides P4 and P5 were employed.     

The effect of ultrafiltered fish protein hydrolysate level on growth performance,protein digestibility and mRNA expression of PepT1 in juvenile turbot (Scophthalmus maximus L.)

The intention of the study was to investigate the effect of ultrafiltered fish protein hydrolysate (UF) level on growth, feed utilization, apparent digestibility coefficients and proximal intestine peptide transporter 1 (PepT1) mRNA level for juvenile turbot (Scophthalmus maximus L.). Experimental diets (UF‐0, UF‐5, UF‐10, UF‐15 and UF‐20) were prepared containing about 68% plant protein, and fish meal protein was, respectively, replaced by 0%, 5%, 10%, 15% and 20% UF of dietary protein. Diet PP contained about 78% plant protein, and diet CAA contained about 10% crystalline amino acid mixture. All diets were fed to seven triplicate groups of turbot (initial weight 16.05 ± 0.03 g) for 68 days. Fish fed diet UF‐10 had an increasing tendency in growth compared with diets contained UF, while dietary UF level was not significantly correlated with specific growth rate and feed intake. Feed efficiency, protein efficiency ratio and protein productive value significantly correlated with dietary UF level, and fish fed diets contained low‐level UF had higher digestibility than that diets UF‐0, PP and CAA. There was a decreasing tendency in PepT1 expression level with dietary UF level. The results indicated that low‐level UF showed a positive effect on growth and feed utilization in juvenile turbot.     

Multimodel approaches in shark and ray growth studies: strengths,weaknesses and the future

Multimodel frameworks are common in contemporary elasmobranch growth literature. These techniques offer a proposed improvement over individual growth functions by incorporating additional candidate models with alternative characteristics. Sigmoid functions (e.g. Gompertz and logistic) are a popular alternative to the commonly used von Bertalanffy growth function (VBGF) as they are hypothesized to better suit certain taxa based on body shape (such as batoids) or reproductive mode (such as egg‐layers). However, this hypothesis has never been tested. This study examined 74 elasmobranch multimodel growth studies by comparing the growth curves of their respective candidate models. Hypotheses regarding model performances were rejected as the VBGF was equally likely to fit best for all taxa and reproductive modes. Subsequently, no individual model was suited to be used a priori. Differences between candidate model fits were greatest at age zero with Gompertz and logistic functions providing estimates that were 15% and 23% larger on average than the VBGF, respectively. However, length‐at‐age estimates of the different models became negligible at older ages. Differences between candidate models were mostly small (≤5%), and the multimodel framework only marginally affected length‐at‐age estimates. However, there were cases where some candidate models provided inappropriate fits that contrasted considerably to the best fitting model. In some of these instances, a single‐model framework could have yielded biologically unrealistic growth estimates. Therefore, no study could pre‐empt whether or not it required a multimodel framework. A framework was subsequently recommended to maximize the accuracy of model fits for elasmobranch length‐at‐age estimates using multimodel approaches.     

Bacterial Flora in Turbot Scophthalmus maximus Cultured in Deepwell Seawater of Liaodong Peninsula

The microbial flora in turbot (Scophthalmus maximus) cultured in deepwell seawater from Liaodong Peninsula, China was studied for the first time. The total amount of aerobic meso- and psychrophilic microflora from the culturing water, gills, and skin were 3.46–3.82, 3.19–4.28, and 1.70–1.95 log cfu/g, respectively. Out of 204 strains isolated from fresh turbot meat with skin, Gram-positive bacteria accounted for 19.2% of the total aerobic meso- and psychrophilic microflora, and 72.1% were Gram-negative bacteria. Phylogenetic analysis was performed using 16S rDNA sequences of microbial flora isolated from turbot. The predominant bacteria in fresh turbot were Micrococcus, Serratia liquefaciens, and Enterobacteriaceae. Meanwhile, the bacterial flora of refrigerated turbot fish were investigated, and the results indicated that Shewanella putrefaciens was the predominant spoilage bacteria.     

Phosphate-limited growth and uptake kinetics of the marine prasinophyte Tetraselmis suecica (Kylin) Butcher

The marine prasinophyte Tetraselmis suecica was grown in a chemostat culture system over a series of phosphate-limited growth rates ranging from 0.164 to 0.755 d^? 1. The relationship between phosphate concentration and growth rate was well described by the Monod equation with a half-saturation constant of 3.45 nM. The kinetics of short-term uptake of phosphate spikes were well described by the Michaelis–Menten equation, maximum uptake rates being 2–3 orders of magnitude higher than associated growth rates. The relationship between cellular carbon-to-phosphorus ratios and growth rates was consistent with the Droop formulation of nutrient-limited growth, and chlorophyll a/carbon ratios were linearly related to growth rate. The protein content of the cells inferred from calculated nitrogen-to-carbon ratios ranged from a minimum of ~ 7% at zero growth rate to a maximum of ~ 59% at a relative growth rate of 1.0. Control of the relative growth rate of T. suecica via selection of the phosphate concentration in the growth medium and dilution rate of the culture appears to be an effective and practical way to manipulate the biochemical composition of this species in order to maximize its nutritional value to invertebrate consumers in aquaculture systems.     

Water quality and nitrogen budget in turbot Scophthalmus maximus culture system supplemented with lactic acid bacteria

To understand the nutrient utilization efficiency and distribution in indoor fish culture system under treatment of probiotics, this study examined water quality and nitrogen budget in turbot Scophthalmus maximus culture system supplemented with four strains of lactic acid bacteria (LAB) isolated from fishery products. The results showed that the concentration of ammonia nitrogen (NH?‐N) and nitrite nitrogen (NO?‐N) in LAB treatments were all significantly lower (p < 0.05) than in the control group. The nitrate nitrogen (NO?‐N) in LAB treatments showed no significant differences (p > 0.05) compared with control group. The fish feed and water exchange accounted for 79.07% and 17.02% of total N input respectively. For N output, the drainage and residual diets in LAB treatment accounted for 24.50%–25.80% and 1.33%–1.60% respectively, and they were significantly lower than in the control group (27.60% and 2.20% respectively). Fish growth and lost N in LAB treatments accounted for 27.10%–30.50% and 11.00%–18.50% respectively, and they were both significantly higher (p < 0.05) than in the control group (22.30% and 5.30% respectively). The results indicated that the indigenous LAB strains were capable of improving fish growth, and reducing NH?‐N and NO?‐N level (at concentration of 10⁵ cfu/ml) by directly adding in S. maximus culture water. Moreover, specific strains of LAB may increase nitrogen loss by promoting denitrification process in culture system.     

水中Mn(Ⅱ)对大菱鲆幼鱼生长及碱性磷酸酶和超氧化物歧化酶活性的影响

水温14~16℃下,将初始体质量为(5.0±1.0)g的大菱鲆养殖在40L水体的水族箱中,研究在不同Mn(Ⅱ)质量浓度(0.04、0.08、0.16、0.32、0.64、1.28、2.56、5.12、10.24mg/L)下大菱鲆的生长及碱性磷酸酶和超氧化物歧化酶的活性。结果表明,当水体中Mn(Ⅱ)质量浓度低于2.56mg/L时,鱼的生长较快,其中Mn(Ⅱ)质量浓度为0.64mg/L时生长最快;当Mn(Ⅱ)质量浓度低于0.64mg/L时,大菱鲆肝脏的碱性磷酸酶和超氧化物歧化酶活性随着Mn(Ⅱ)质量浓度的提高而增加,当Mn(Ⅱ)质量浓度超过0.64mg/L时,碱性磷酸酶和超氧化物歧化酶的活性急剧下降;0.64mg/L组的碱性磷酸酶和超氧化物歧化酶的活力均较高,随着Mn(Ⅱ)质量浓度增加,碱性磷酸酶和超氧化物歧化酶的活力先增后减;据剂量效应推测,0.64mg/L为Mn(Ⅱ)表现出毒性作用的临界质量浓度。     

The effects of ration level on feed intake and growth, and compensatory growth after restricted feeding, in turbot Scophthalmus maximus L.

Feed intake and growth were studied in groups of turbot fed daily rations of 0.25%, 0.38% and 1% of body weight day^–1 for 41 days. Then, all groups were fed 1% of body weight day^–1 for the next 34 days. The two restricted rations resulted in reduced growth rates (30% and 60% of fully fed controls), and there was a tendency for increased growth heterogeneity (coefficient of variation increased from about 100% to about 150%) compared with controls on full rations. Nevertheless, restricted rations did not result in any increase in size heterogeneity with the passage of time: the coefficient of variation for weight changed little irrespective of feeding treatment. The turbot became hyperphagic and displayed compensatory growth after the change from restricted to excess feeding, with compensatory growth being most marked among the fish that had been subject to the most severe feed restriction. The results provided some evidence of increased variability in feeding and growth within groups of turbot fed restricted rations, possibly as a result of the establishment of weak feeding hierarchies. When feeding restrictions were lifted, the turbot that had reduced growth under feed restriction were able to completely compensate for lost growth.