Growth Of European Sea Bass Research Articles

Dietary inclusion of blood hydrolysates affects muscle growth in European seabass (Dicentrarchus labrax)

Dietary supplementation with hydrolysates has been suggested to influence muscle protein synthesis and fish growth. This study assessed the impact of including 3% swine blood hydrolysates (BH) in a plant-based diet on muscle cellularity and the expression of molecular markers related to muscle fibre proliferation and hypertrophic growth of European seabass. Three BH fractions were obtained by two different processes, autohydrolysis (AH-H) and enzymatic hydrolysis followed by micro- (RMF-H) and nanofiltration (RNF-H). Each BH was added to a commercial-based diet, where 50% of fishmeal was replaced by vegetable proteins (negative control, NC). A fishmeal-based diet was used as positive control, PC. The diets were fed to juveniles (12 g) during 74 days. The RMF group showed down-regulation of myod1 and fgf4, essential to myoblast proliferation and differentiation, and upregulation of mafbx, responsible for protein breakdown, resulting in impairment of muscle hyperplasic growth and the lowest muscle fibres number. However, compensatory growth mechanisms were observed through capn1 downregulation and mymk upregulation, suggesting decreased muscle proteolysis and increased myoblast fusion. Despite this, the compensatory mechanisms were insufficient as RMF group had the worst growth. RNF group had a final weight similar to the NC, but downregulation of fgf4, fgf6 and capn1 may compromise growth potential at long term. The expression of these genes in the AH group was similar to that in the FM-based diet. Despite not having demonstrated growth promotion ability, BH affect muscle growth and cellularity factors, prompting further research on commercial-sized fish to reveal their impact on important commercial traits.

Nutritional innovations in superior European sea bass (Dicentrarchus labrax) genotypes: Implications on fish performance and feed utilization

The sustainable development of the aquaculture industry relies on the use of alternative conventional and emergent raw materials that contributes to a circular economy and to reduce the dependency on fish meals and fish oils coming from oceanic fish populations. Additionally, the genetic selection of farmed fish that can display higher growth and feed utilization when fed alternative feeds, is pointed out to be a complementary valuable tool to facilitate the implementation of circular economy approaches. The main purpose of the present study was to determine the effectiveness of genetic selection for growth in European sea bass, in response to a challenge with an alternative diet that aimed to partially replaced fishmeal (FM) by poultry meal (PM) and totally replace fish oil (FO) by a blend of poultry oil (PO) with a novel microalgae oil. The two families of fish juveniles were obtained by in vitro fertilization of selected for a multi-trait including high growth (genetically selected, GS) or non-selected (wild type, WT) broodstocks and then were nutritionally challenged with a control diet that mirrored a standard commercial diet with fishmeal (20%) and fish oil (7%), or a Future diet that partially replaced the FM by PM and totally replaced the FO by a blend of rapeseed oil, PO, and a novel DHA rich-algal oil. From the second month of feeding until the end of the trial, European sea bass that was selected since for 7 generations performed better in terms of growth than the wild-type genotype, possibly related with an apparent favored feed and nutrient utilization. Furthermore, selection decreased the perivisceral fat and increased the nutritional value of flesh by increasing DHA (in g/ 100 g flesh) and ARA contents. In contrast, the dietary treatment showed little effect on fish growth performance, denoting the successful partial replacement of FM by PM and the total replacement of FO by a blend of poultry oil and an emergent microalgal oil. However, Future diet tended to reduce the ADCs of some amino acids, as well as showed an additive effect to genotype in increasing the n-3 PUFA of flesh. Altogether, our data demonstrate that multi-trait genetic selection of European sea bass improve fish plasticity to cope with the variations of ingredients in alternative feeds with low FM/FO.

Genome Wide Association (GWAS) Analysis and genomic heritability for parasite resistance and growth in European seabass

There is an increasing demand for the breeding programs to focus on resistance against diseases since the treatments or vaccinations increase production costs and, in some cases, they are not available at all. Most of the studies focus on virus and bacterial diseases, but limited information is available for parasitic diseases in European seabass. A sample of infected fish (985) with Lernanthropus kroyeri and their parents were genotyped using the recently developed MedFISH SNP array. The sample was selected (selective genotyping) in order to capture the genetic variation of the resistance against the Lernanthropus kroyeri. Body weight was recorded at different growth stages in the population. The genetic parameters were estimated for body weight and parasite count, using Restricted Estimation Maximum Likelihood (REML) methods utilizing a Genomic Relationship Matrix (GRM). Additionally, univariate GWAS, multitrait GWAS and Regional Heritability Mapping (RHM) were performed in order to identify genomic areas related to host resistance and growth. A moderate genomic heritability was detected for growth at sea cage (0.39) and for weight at 2, 4, 6 months after the fish were transferred to the sea cage (0.46–0.41). A moderate to low genomic correlation between growth (body weight/growth at the sea cage) and parasites was observed (0.36–0.21). GWAS results indicated two putative QTL affecting host resistance to Lernanthropus kroyeri count, each one of them explaining approximately 2% of the phenotypic variation.

Recovery of Haemal Lordosis in European Seabass Dicentrarchus labrax (Linnaeus 1758)

Lordosis of the haemal part of the vertebral column is a frequent abnormality in reared fish. Haemal lordosis develops during the late larval and early juvenile life stages of fish, mainly due to the high swimming activity of the fish in the rearing tanks. In the present study, we have examined whether haemal lordosis recovers during the growth of European seabass. Furthermore, we aimed to develop simple morphometric indices (PrAn1 and PrAn2) that might link the severity of lordosis at the juvenile stage with fish morphological quality at harvesting. At 111 days post-hatching (dph, 53 ± 4 mm standard length, SL), 600 seabass juveniles with lordotic (L, 200 fish) or normal (N, 400 fish) external morphology were selected and introduced in a common tank. At 150 dph (75 ± 7 mm SL), 350 fish were randomly selected, pit-tagged and transferred to a sea cage for on-growing up to 502 dph (234 ± 16 mm SL). The morphological examination of the fish at 150 and 502 dph revealed that 60% (46 out of 77) of L juveniles turned into normal phenotype by the end of on-growing period. Interestingly, 56% of the fish with recovered external morphology (N-Rec) presented either a completely normal vertebral column (31%) or minor abnormalities of individual vertebrae (25%). Following the results of geometric morphometric analysis, the differences in the body shape between N-Rec and N fish were not statistically significant (p > 0.05, canonical variate analysis). The examined morphometric indices were effective in discriminating the normal fish from 58% (PrAn1) to 65% (PrAn2) of lordotic juveniles. Results are discussed with respect to the mechanism of lordosis recovery, and spotlights on their application for quality control and cull out of the abnormal fish in commercial hatcheries.

On the trail of detecting genetic (co)variation between resistance to parasite infections (Diplectanum aequans and Lernanthropus kroyeri) and growth in European seabass (Dicentrarchus labrax)

The European seabass is one of the main commercial fish produced in Mediterranean marine aquaculture. Recently, its production has been negatively affected by losses due to frequent and recurring outbreaks of parasitic, bacterial and viral diseases. In recent years, the gill parasites Diplectanum aequans and Lernanthropus kroyeri are increasingly becoming more dominant and contributing more significantly to the observed losses. Genetic improvement for disease resistance represents an important strategy for controlling infectious diseases in farmed fish by increasing their robustness. In order to determine the possibility of including such trait in selective breeding programs, we need to comprehend whether additive genetic variation for resistance against Diplectanum aequans and Lernanthropus kroyeri exists. For this purpose, two open-sea parasite cohabitation trials (for two consecutive years) were performed in the commercial production sites of a private company (Nireus S.A), that had high infestation with Diplectanum aequans and Lernanthropus kroyeri. Juvenile European seabass (9425 offspring from 91 full-sib and half-sib families per year), originating from the company's breeding program were equally divided into two groups and transferred to two commercial farming sites located in the areas of Nafpactos and Sagiada, in western Greece, for the intended cohabitation studies. The parasite numbers on all the gill arches were counted and recorded at the end of the trials for the infestation levels. A third site (Palairos) without any parasite infestation was used as a control site. A multi-trait animal model was used to estimate the variance-covariance components and to evaluate the genetic parameters for Parasite Counts, recorded from all the gill arches of the fish, and their corresponding growth in sea cages. The estimated heritabilities for parasite count, using untransformed data, were 0.20 (D. aequans) and 0.28 (L. kroyeri) and for transformed data 0.29 and 0.26, respectively. The heritability estimates for body weight were 0.42−0.51 for D. aequans and 0.28−0.51 for L. kroyeri trials. Similarly, estimated heritabilities for the growth in sea cages were 0.43 and 0.29, respectively. Although parasite count has a low to medium unfavorable genetic correlation with body weight and growth (0.09−0.37), it seems that it is not significantly impairing selection for growth. Furthermore, the results of this study are very promising in terms of the existing potential for genetic improvement of parasite resistance, and provides a good basis for further genetic analysis using molecular markers.

Effect of Micro Particulate Diets and Different Weaning Periods on Survival and Growth of European Sea Bass (Dicentrarchus labrax) Larvae

Effect of Micro Particulate Diets and Different Weaning Periods on Survival and Growth of European Sea Bass (Dicentrarchus labrax) Larvae

The Effects of Dietary Vitamin C Levels on Tissue Ascorbic Acid Concentration and Growth in European Sea Bass (Dicentrarchus labrax, L.1758)

The effect of different dietary levels of L-ascorbic acid on the growth and vitamin C concentration in the tissue of European Sea bass (Dicentrarchus labrax, L.1753) with an initial body weight of 4.6±1.1 g was studied. Four practical diets were formulated to containing 10 (AA10), 25 (AA25), 42 (AA42) and 65 (AA65) mg ascorbic acid equivalent kg-1 diet. The results of a 20 week feeding trial showed that typical vitamin C-deficiency signs and high mortality in the fish fed with the AA10 diet. The fish fed with AA42 (42 mg kg-1 AA diet) showed a significantly higher final body weight than the other diets (P less than 0.05) and the concentrations of ascorbic acid (AA) in the brain of these fish were higher than in the other experimental group (P less than 0.05). In this study, the amount of storage in the organs occurred in this order: brain, kidney, liver.

Development of a liquid chromatography atmospheric pressure chemical ionization mass spectrometry method for determining off-flavor compounds and its application toward marine recirculating aquaculture system monitoring and evaluation of aeration as a depuration approach

The off-flavor compounds geosmin and 2-methylisoborneol (2-MIB) are well-known to impact the quality of farmed freshwater fish species, but little is known about off-flavors in marine aquaculture. To begin addressing this knowledge gap, a method for determining geosmin and 2-MIB using LC with atmospheric pressure chemical ionization (APCI) MS detection was developed. While 2-MIB was readily detected using LC-APCI/MS, geosmin exhibited on-column degradation that was independent of column chemistry and could not be eliminated. Optimized conditions were identified that balanced the separation and ionization efficiency of 2-MIB and geosmin while minimizing geosmin degradation, but the overall method sensitivity for geosmin was reduced by the on-column losses. The method was used with direct aqueous injections to determine the volatilization rates of geosmin and 2-MIB at ppb levels during aeration under laboratory conditions in both salt water and pure water to simulate marine and fresh water aquaculture, respectively. The volatilization rates of both compounds were 30% faster in salt water than in fresh water with or without aeration, but aeration was found to enhance the rate by a factor of 2.5 in both water types. The LC-APCI/MS method was combined with stir bar sorptive extraction (SBSE) to achieve greater sensitivity for determining off-flavors in recirculating aquaculture system (RAS) water. Using SBSE-LC-APCI/MS, the LODs for geosmin and 2-MIB were 70 ng/kg (part per trillion) and 6 ng/kg, respectively. The on-column losses resulted in a relatively high LOD for geosmin that renders this method unsuitable for determining geosmin at the low ng/kg levels expected in RAS. SBSE using both grab water samples and an in-situ diving unit were used to evaluate 2-MIB levels in the culture water of two separate marine RAS that were supporting the growth of European sea bass but had differing levels of water treatment. 2-MIB was readily detected using both SBSE approaches in the RAS with less sophisticated treatment when the animal stocking density was at its highest (50 kg/m3) but was not detected in the more sophisticated RAS regardless of stocking density. Geosmin was not detected in either system, but the results were inconclusive given its higher LOD. These limited results suggest that the anaerobic water treatment components, present only in the more sophisticated RAS, maintained the level of 2-MIB below the LOD.

Effects of dietary scallop and squid hydrolysates on growth of European seabass, Dicentrarchus labrax; California yellowtail, Seriola lalandi; and barramundi, Lates calcarifer

Squid processing byproducts and scallop viscera were homogenized and subjected to hydrolysis at 55°C for 1.5 hr, followed by pasteurization at 75°C for 30 min. The respective hydrolysates were incorporated into diets in which 30–70% of fishmeal (FM) was replaced with soybean meal (SBM) and evaluated as is (wet), dried, or impregnated into SBM for their effects on growth of European seabass, Dicentrarchus labrax; California yellowtail, Seriola lalandi; and barramundi, Lates calcarifer, in a series of 8‐week experiments. No adverse thermal deterioration in the quality of hydrolysate occurred because of drum drying, compared to the wet hydrolysate. No differences were observed in growth of California yellowtail between SBM mixed with dry hydrolysate and SBM impregnated with wet hydrolysate. Dietary inclusion of hydrolysate improved feed attractability and growth and was beneficial in the early juvenile stage but not in the growout stage for European seabass and California yellowtail. However, in barramundi, no discernable benefit was observed from the addition of hydrolysates. The improved feed attractability and growth appear to be dependent on species and type of hydrolysate. The texture of fillets of yellowtail fed 70% FM replacement with SBM + squid hydrolysate diets was significantly firmer than without squid hydrolysate.

Effect of fishmeal and fish oil replacement by vegetable meals and oils on gut health of European sea bass (Dicentrarchus labrax)

The main objective of this study was to assess the effects of graded levels of replacement of fishmeal (FM) and fish oil (FO) by terrestrial meals (TM) and vegetable oils (VO) on gut health of European sea bass (Dicentrarchus labrax) based on gut morphology, gut-associated immune system (GALT) and gut microbiota composition. Reducing the dietary FM and FO levels down to 10 and 3%, respectively did not affect the growth of European sea bass. Increase in TM and VO markedly affected anterior and posterior gut morphology and fatty acid composition, which mirrored the dietary fatty acid profile. FO replacement by VO increased lipid deposition in anterior gut lamina propria, denoting an effect in lipid metabolism and lipoprotein synthesis. In posterior gut, FM replacements by TM induced an engrossment of the submucosa, an up-regulation of the proinflammatory cytokines IL-1β and TNFα genes, a relatively high mucus production and changes in mucosal microbiota profiles. Finally, supplementation of 0%FM-0%FO diets with LC-PUFA contributed to maintain gut homeostasis in terms of GALT response and microbiota profiles alterations. Statement of relevanceFM and FO appropriate dietary levels for European seabass

Effect of Early Weaning on Survival and Growth of European Sea Bass, Dicentrarchus Labrax Larvae Using an Equal Mixture of Sea and Well Water

Effect of Early Weaning on Survival and Growth of European Sea Bass, Dicentrarchus Labrax Larvae Using an Equal Mixture of Sea and Well Water

Bone morphogenetic protein 15 and growth differentiation factor 9 expression in the ovary of European sea bass ( Dicentrarchus labrax): Cellular localization, developmental profiles, and response to unilateral ovariectomy

Vertebrate oocytes actively contribute to follicle development by secreting a variety of growth factors, among which bone morphogenetic protein 15 (BMP15/Bmp15) and growth differentiation factor 9 (GDF9/Gdf9) have been paid particular attention. In the present study, we describe the cellular localization, the developmental profiles, and the response to unilateral ovariectomy (a procedure implying the surgical removal of one of the ovaries) of protein and mRNA steady-state levels of Bmp15 and Gdf9 in the ovary of European sea bass, an important fish species for marine aquaculture industry. In situ hybridization and immunohistochemistry demonstrated that the oocyte is the main production site of Bmp15 and Gdf9 in European sea bass ovary. During oocyte development, Bmp15 protein expression started to be detected only from the lipid vesicle stage onwards but not in primary pre-vitellogenic ( i.e. perinucleolar) oocytes as the bmp15 mRNA already did. Gdf9 protein and gdf9 mRNA expression were both detected in primary perinucleolar oocytes and followed similar decreasing patterns thereafter. Unilateral ovariectomy induced a full compensatory growth of the remaining ovary in the 2-month period following surgery (Á. García-López, M.I. Sánchez-Amaya, C.R. Tyler, F. Prat 2011). The compensatory growth elicited different changes in the expression levels of mRNA and protein of both factors, although the involvement of Bmp15 and Gdf9 in the regulatory network orchestrating such process remains unclear at present. Altogether, our results establish a solid base for further studies focused on elucidating the specific functions of Bmp15 and Gdf9 during primary and secondary oocyte growth in European sea bass.

A first insight into genotype × diet interactions in European sea bass (Dicentrarchus labrax L. 1756) in the context of plant-based diet use

This preliminary study assessed genotype _ diet interaction in late growth of European sea bass (Dicentrarchus labrax) fed with either a ￠sh meal (FM)- or a ￠sh oil (FO)-based diet (M) or an all-plant-based (PB) diet. Atotal of 550 ￠sh from 224 families were reared together and tagged. DNAwas sampled and microsatellites were used to assign parentage. When ￠sh weight was 192 _ 54 g, two tanks were fed with M (FM: 100%; FO: 100%) and two others with PB (FM: 0% and FO: 0%). Body weight (BW), fork length (FL) and ￠llet lipid content (CorrFat) were analysed with a linear model and with REML methodology.We observed no signi￠cant di!erences between groups, but a slightly lower (P50.03) daily growth coe⁄cient in sea bass fed PB than in those fed M. Heritability estimates of BWdi!ered signi￠cantly from zero (PB: 0.37 _ 0.18; M: 0.47 _ 0.24). Sire _ diet interactions were signi￠cant and genetic correlations ranged between 0.51 and 0.87, showing genotype _ diet interaction for BWand CorrFat. For the ￠rst time, genetic parameters in the context of total replacement of marine ￠shery by-products were estimated in European sea bass, showing re-ranking of family performances with extremely contrasted diets.

Genotype by environment interactions for growth in European seabass ( Dicentrarchus labrax) are large when growth rate rather than weight is considered

Two hundred fifty three full-sib families from 33 males and 23 females of European seabass were produced in a partly factorial mating design. All fish were reared in the same tank for 14 months until reaching mean weight of 35 g, then 7000 of them were individually tagged and weighed, and dispatched to four farms in different locations (France, Israel, Italy and Portugal) representing a wide variety of environmental conditions. Around mean weight of 400 g, 1177 to 1667 fish at each site were weighed. Daily growth coefficient (DGC) was calculated. Pedigrees were successfully redrawn for 99.2% of fish using microsatellite markers. Genetic correlations between sites were high for body weight (> 0.80 in all cases but one, i.e., five cases over six), but only moderate for DGC (0.21–0.61), with one exception. This indicates significant G × E interactions for growth rate, which were not revealed when studying body weight due to shared common environment of the fish prior to separation to the different rearing environments.

Otolith growth of European sea bass (<em>Dicentrarchus labrax</em> L.) larvae fed with constant or varying food levels

in the late-feeding larvae (food available from 13 DAH), increment width increased progressively once food was supplied, and reached values similar to those for fed larvae after one week of feeding. Deprivation of food for two days in post-flexion larvae (in the fourth week of larval development) was reflected in the formation of progressively narrower increments which had still not returned to normal width two days after feeding was resumed. our results show that the width of the outermost otolith increments reflect the past feeding history and that the rogi can be used to distinguish well fed from suboptimally nourished larvae.

Production and characterization of recombinantly derived peptides and antibodies for accurate determinations of somatolactin, growth hormone and insulin-like growth factor-I in European sea bass ( Dicentrarchus labrax)

A specific radioimmunoassay (RIA) for European sea bass ( Dicentrarchus labrax) growth hormone (GH) was developed and validated. For this purpose, a stable source of GH was produced by means of recombinant DNA technology in a bacteria system. The identity of the purified protein (ion exchange chromatography) was demonstrated by Western blot and a specific GH antiserum was raised in rabbit. In Western blot and RIA system, this antiserum recognized specifically native and recombinant GH, and it did not cross-react with fish prolactin (PRL) and somatolactin (SL). In a similar way, a specific polyclonal antiserum against the now available recombinant European sea bass SL was raised and used in the RIA system to a sensitivity of 0.3 ng/ml (90% of binding of tracer). Further, European sea bass insulin-like growth factor-I (IGF-I) was cloned and sequenced, and its high degree of identity with IGF-I peptides of barramundi, tuna, and sparid fish allowed the use of a commercial IGF-I RIA based on barramundi IGF-I antiserum. These assay tools assisted for the first time accurate determinations of SL and GH–IGF–I axis activity in a fish species of the Moronidae family. Data values were compared to those found with gilthead sea bream ( Sparus aurata), which is currently used as a Mediterranean fish model for growth endocrinology studies. As a characteristic feature, the average concentration year round of circulating GH in growing mature males of European sea bass was higher than in gilthead sea bream. By contrast, the average concentration of circulating SL was lower. Concerning to circulating concentration of IGF-I, the measured plasma values for a given growth rate were also lower in European sea bass. These findings are discussed on the basis of a different energy status that might allowed a reduced but more continuous growth in European sea bass.

Effect of chronic ammonia exposure on growth of European seabass ( Dicentrarchus labrax) juveniles

Chronic effects of ammonia were studied in juvenile seabass, Dicentrarchus labrax (mean weight=11 g), exposed for 63 days to eight stable ammonia concentrations, ranging from 0.24 to 0.90 mg l −1 unionised ammonia nitrogen (UIA-N), respectively, from 6.1 to 22.3 mg l −1 total ammonia nitrogen (TA-N). Temperature (21.8 °C), pH (8.0), salinity (37.0 ppt), and oxygen concentration (over 80% saturation at the outlet) were maintained constant. Fish were fed using a self-feeder device, and they were starved during the last 8 days. Mortality of 28.9 and 42.6% occurred within the first 8 days at the two highest UIA-N concentrations, respectively, 0.90 and 0.88 mg l −1. From days 0 to 55, a 1.8-fold increase in weight gain was observed under the 0.90-mg l −1 UIA-N condition, compared to a 3.4-fold increase in the control. Weight gains were negatively correlated to ambient ammonia concentrations. Weight loss, or a transient period of growth stagnation, was observed from the onset of ammonia exposure to day 13 in seabass exposed to concentrations above 0.43 mg l −1 UIA-N. After day 13, weight gains were observed in all groups, indicating that the fish were able to adapt to increased ambient ammonia concentrations over time. By the end of the experiment, plasma ammonia levels were positively related to ambient ammonia concentrations, and oxygen consumption recorded in fasting fish was significantly dependent on ammonia concentrations. In seabass juveniles, the 0.26-mg l −1 UIA-N concentration, under an average pH of 8.0, can be considered as a safe long-term limit conditions in seawater.

European sea bass growth and N and P loss under different feeding practices

This study was performed to assess growth rate, feed efficiency, and N and P loss of sea bass (initial body weight 3.5 g), held in 500-l tanks under ambient temperature and natural light, and fed according to the following methods: by automatic feeders that released feed continually in daylight according to feed manufacturers' recommendations (AF100%); half of the above continually in daylight (AF50%); half of the above again but in two meals only (AF50%M); and by self-feeders that supplied feed at low (SFL), medium (SFM) and high (SFH) reward. None of the feeding conditions affected the survival rate of fish. SFL fish had the highest specific growth rate, while AF50% and AF50%M the lowest. Population weight distribution in the restricted automatic-fed fish (AF50% and AF50%M) was more homogenous compared to the other feeding conditions. These two practices produced high feed efficiency ratios (0.93 and 0.95, respectively), compared to the AF100% (0.57) and self-fed ones (SFL: 0.60; SFM: 0.37; SFH: 0.21). Self-feeding at low reward of 0.6 g trigger −1 could be considered as the optimum feeding practice, combining higher weight gain, lower N and P loss, and intermediate feed supply compared to the other treatments. In the SFH method, fish did not adjust their manipulation of the self-feeders according to their feed needs. Daily feeding activity in all self-fed fish groups was independent of feeding reward.

Growth of European sea bass ( Dicentrarchus labrax L.) under hypoxic and oscillating oxygen conditions

Effects of moderate hypoxia and oscillating oxygen conditions on growth of European sea bass ( Dicentrarchus labrax L.) were investigated. Groups of four to six sea bass (initial weights 40–90 g) were exposed to one of three oxygen regimes (40% air saturation; oscillations between 40–86% with a period of 770 min; 86% as a control) at 22°C and a salinity of 37 for 1 month. All fish survived and gained weight, but relative to the controls, the sea bass exposed to hypoxic conditions consumed significantly less food, exhibited a reduced growth, and had a lower condition factor. Oscillating groups were intermediate, and not statistically distinguishable from either normoxic or hypoxic treatments. Feed conversion efficiency and variation in body size were not significantly affected by oxygen conditions. Growth was correlated with feed intake, suggesting that reduced growth under moderate hypoxic or oscillating oxygen conditions is primarily due to reduced appetite and not a consequence of a decrease in feed conversion efficiency.

Effect of three feeding strategies (automatic, ad libitum demand-feeding and time-restricted demand-feeding) on feeding rhythms and growth in European sea bass ( Dicentrarchuslabrax L.)

We studied the effect of automatic-feeding (A), ad libitum demand-feeding (D) and time-restricted demand-feeding (RD) on the feeding rhythm and growth performance of European sea bass maintained under natural summer conditions. RD and A had access to feed during three meals a day of 1 h duration each (08:00–09:00, 16:00–17:00 and 00:00–01:00). Feeding demands in D showed daily rhythms that varied according to both water temperature and photoperiod. When submitted to system RD, their feeding patterns were strongly associated with periods of feed availability. Feeding strategies affected both biomass increase and feed efficiency ratio, the worst results being obtained in A. On the other hand, the feeding system had no effect on body composition nor on weight homogeneity of the different groups. These results showed that sea bass can adapt to different feeding strategies, although for maximum benefit to be gained from the diet, these strategies should reflect the feeding rhythms of the fish.