Early assessment of gilthead sea bream (Sparus aurata) spawning dynamics by mini‐broodstocks

The implementation of any sustainable breeding program requires a maximization of effective size (Ne) to maintain inbreeding rate at minimum levels. However, the control of Ne remains a major challenge for those species whose reproduction in captivity is based on a spawning strategy where there is no control over the established matings. The present study aims to assess the spawning dynamic of gilthead sea bream (Sparus aurata) at different dates from two mini‐broodstocks (4 ♀ and 4 ♂). Here we report the use of a simple protocol based on the genotyping of fertilized eggs from a reduced set of microsatellite loci which provides a quick evaluation of daily spawning in terms of family structuring (number of active breeders and number and family size). According to our results, the daily spawning dynamics is characterized by a fluctuation in the number of active breeders, reaching maximum values (until 100%) during peak production phase. However, the proportion of possible mating (families) in a single daily spawning never exceeded more than 81%. Unbalanced parental contributions were highly frequent, with extreme cases involving the assignment of 50%–90% of the offspring to a single family. Therefore, the use of mini‐broodstocks and the grouping of spawning harvested at different dates are proposed as strategies to minimize the inbreeding risk by providing a more optimal pattern of family structuring (increase in the number of families obtained and a more balanced parental contributions) that entails a more conservative Ne/N ratio.     

Genetic variation in farmed populations of the gilthead sea bream Sparus aurata in Greece using microsatellite DNA markers

Genetic variation in seven reared stocks of gilthead sea bream Sparus aurata, originating from Greek commercial farms, was assessed using five polymorphic microsatellite markers and was compared with that of two natural populations from the Ionian and the Adriatic Seas. The total number of alleles per marker ranged from 11 to 19 alleles, and hatchery samples showed the same levels of observed heterozygosity with samples from the wild but substantially smaller allelic diversity and expected heterozygosity. The global genetic differentiation for the cultivated samples was significant as indicated by F_st analysis, which might indicate random genetic drift and inbreeding events operating in the hatcheries. On the contrary, no significant difference was found between the two wild populations. Population pairwise tests between farmed and wild stocks were also significant, with the exception of one hatchery sample, the Central Greece 1, which was not significantly different from the two wild samples perhaps due to its recent use in aquaculture from wild‐caught animals. The UPGMA tree topology grouped the wild samples together with the Central Greece 1 stock, and showed a clear division between wild and farmed sample sets for the six remaining hatchery samples. Knowledge of the genetic variation in S. aurata cultured populations compared with that in the wild ones is essential for setting up appropriate guidelines for the proper monitoring and management of the stocks either under traditional practices or for the implementation of selective breeding programmes.     

Morphological and histological characterization of an ectopically mineralized structure in a gilthead sea bream Sparus aurata with opercular deformation

In this study, we describe an abnormal ectopically mineralized structure (EMS) that was found inside the skull of a juvenile Sparus aurata that also showed a bilateral opercular deformation. The overall phenotype and tissue composition were studied using micro‐CT scanning and histological analyses. The ectopic structure occupies a large volume of the brain cavity, partially extruding into the gill cavity. It shows a dense mineralization and an extracellular matrix‐rich phenotype, with variation in both the morphology and size of the cell lacunae, combined with an irregular fibre organization inside the matrix. This study is the first to report such an EMS in a juvenile teleost fish, where the tissue does not resemble any other connective tissue type described in bony fish so far. The tissue phenotype seems to rule out that the EMS corresponds to a tumorous cartilage. Yet, it is rather reminiscent of a highly mineralized structure found in cartilaginous fish, where it is suggested to be associated with damage repair.     

A behavioural approach of dominance establishment in tank‐held sea bream (Sparus aurata L.) under different feeding conditions

Dominance is a strong behaviour exhibited by farmed species that very often impinges on fish growth and welfare. This study presents a behavioural approach of dominance, where colour pattern differentiation was tested as a signal of dominance presence in small sea bream population. The phenotype of dominance was first described in detail, referring to vertical dark stripes and splayed fins. Fish were kept in triplicate tanks for 21 days, during which they were exposed to three feeding conditions (well fed, limited fed and no‐fed) and continuous video recordings. Each tank was stocked with 15 individuals (~30.34 ± 1.70 g), and they were confined to the half volume of the tank via a removable net pen. Percentage of dominants per population was found up to 40%, while duration was calculated to 53.52 ± 7.44 s. Dominance behaviour was further quantified via colour pattern differentiation on sea bream body (CDA, contrast of dominance appearance). The results demonstrated that the body colour of sea bream is directly linked to species social hierarchies and such variations are visual signal of dominance rank inside the population. The fish feeding conditions had an influence on the dominance presence, but not on the dominance rank (as measured by the CDA) between fish groups. The described study provides state‐of‐the‐art knowledge on sea bream dominance. In relevance to aquaculture, dominance quantification would be a reliable tool to evaluate non‐equal food distribution in tank‐held populations, thus, avoid non‐regulate growth performance of fish before transfer to sea‐cage installations.     

Effect of diet composition on nutrient digestibility and digestive enzyme levels of gilthead sea bream (Sparus aurata L.)

An experiment was conducted to evaluate the effects of dietary composition on apparent digestibility coefficients of protein, fat and carbohydrate of gilthead sea bream. In addition α‐amylase and proteolytic activities were measured in the digestive tract of fish, held at 20±1°C. Six experimental diets were formulated containing approximately 40%, 45% and 50% protein, 11% and 21% fat and a starch level which fluctuated from 14% to 36%. Fish having an average weight of 100–130 g were used, fed at 1.5% of their body weight daily, and digestibility was measured using an indirect method. Enzyme activities were measured in the digestive tract of fish, fed diets containing a combination of 40%, 50% protein with 11%, 21% fat at 0.5, 5, 10, 24 h after a single meal. Starch digestibility was reduced with its level in the diet. It also negatively affected fat digestibility as well as protein digestibility, the last only at the high fat level. Dietary fat level had a negative effect on starch and protein digestibility. Fat affected also strongly α‐amylase levels in the digestive tract, while its effect on protease activity was of smaller magnitude. These results indicate that digestive enzyme activities and nutrient digestibility values are affected by dietary composition, carbohydrates and fat indicating the strongest effect.     

Insect larvae as feed ingredient selectively increase arachidonic acid content in farmed gilthead sea bream (Sparus aurata L.)

This work is aimed at obtaining farmed fish designed to contain targeted PUFAs. To this end, an experiment was conducted with farmed specimens of gilthead sea bream (Sparus aurata L.), which were fed meal containing different percentages of common green bottle fly (Lucilia sericata Meigen) larvae, cultured on appropriate substrates, and then the fatty acid profiles in fish muscles were determined. Results indicate that arachidonic acid content in fish muscle is significantly increased when replacing different proportions of fishmeal by larvae from L. sericata, which contains arachidonic acid up to 10.6% of total fatty acids. Thus, larvae seem to be a suitable vector for introducing target PUFA in fish muscle and it could also contribute to reduce the use of wild fish stocks for fishmeal production.     

Cottonseed oil as a complementary lipid source in diets for gilthead seabream Sparus aurata juveniles

The efficacy of using cottonseed oil (CSO) as a fish oil (FO) substitute in gilthead seabream (Sparus aurata) juveniles feed was evaluated. Fish (BW_i 4.0 ± 2.9 g) were fed one of four isoproteic (~48% CP) and isolipidic (~18% L) diets for 9 weeks. Added oil was either FO (control diet, CTRL) or CSO, replacing 50% (CSO50 diet), 60% (CSO60 diet) and 70% (CSO70 diet) of dietary FO. Results indicated that FO replacement by CSO up to 60% level had no detrimental effects on growth or nutritive utilization and composition in fish muscles. Higher CSO intake (CSO70 diet, 56 g kg^?1) led to a 16% reduction in weight gain, 14% in feed utilization (FCR) and 57% in muscle n‐3 long‐chain polyunsaturated fatty acids (lc PUFA) as compared with CTRL and to abundant accumulation of lipid within the hepatocytes. Use of CSO altered fatty acid (FA) profiles of muscle and liver. Data suggested utilization of linoleic acid (LOA) by fish and retain of docosahexaenoic acid (DHA) in muscles. Therefore, limits of CSO inclusion as the main source of supplementary dietary lipid, with no negative effects on fish performance or nutritive composition and utilization in muscles, are: 40–48 g kg^?1 feed for gilthead seabream juveniles.     

Quality of reared gilthead sea bream (Sparus aurata) during ice storage,as affected by dietary fish oil substitution; an instrumental and sensory designation approach

The fillet fatty acids (FAs) and volatile compounds (VCs) of gilthead sea bream, fed either fish oil‐based diet (FO) or plant oils (PO), were studied in dorsal and ventral fillet parts over a 12‐day ice storage. Fillet FA reflected the FA composition of the respective diets. Monounsaturated FAs were reduced with storage, while no FA differentiations occurred between fillet parts. VCs varied between diet treatments, with food chain‐transported compounds (α‐pinene and dimethylsulphide) showing higher abundance in the FO group. VCs proposed as fish spoilage indicators (trimethylamine, pentanal, propanal, 3‐methylbutanal and 1‐penten‐3‐ol) increased with storage, while concentration of carbon disulphide associated with fresh fish aroma decreased during the same period. VCs varied between fillet parts, with ventral part exhibiting higher concentrations in fat‐soluble (terpenes, aromatic hydrocarbons) and spoilage‐associated VCs. Sensory analysis revealed no significant differences between diet groups with the exception of fattiness, which was found significantly higher in the plant oil group.     

Growth,tissue metabolites and digestive functionality in Sparus aurata juveniles fed different levels of macroalgae,Gracilaria cornea and Ulva rigida

The aim of this study was to evaluate the inclusion of two macroalgae as dietary ingredients on growth, body composition, intermediate metabolism, intestinal enzymes and gut histology of Sparus aurata juveniles. Six isocaloric and isonitrogenous diets incorporating 5%, 15% or 25% of Gracilaria cornea or Ulva rigida meal were tested against a control diet. Duplicate groups of fifteen fish (14 g) were fed the experimental diets for 70 days. Growth performance showed an inverse linear relationship with the inclusion level of Gracilaria. Feed conversion ratio increased significantly in fish fed 25% Gracilaria. Ulva presented a quadratic relationship with the lowest SGR at 15% of inclusion. Fish fed 25% Ulva exhibited significantly lower lipid content than those fed control diet. Overall, metabolites did not show differences with specimens fed control diet, except for plasmatic glucose and muscle lactate. Intestinal proteolytic activity was reduced with the macroalgae inclusion level, but all fish showed the same enzyme pattern. The histological study revealed no negative effect on liver and intestine structure by the macroalgae inclusion. The present work demonstrated that these ingredients can be used in practical diets for sea bream, but a more comprehensive research is needed to determine the optimum dietary level in a longer feeding trial.     

Amino acid retention of gilthead sea bream (Sparus aurata,L.) fed with pea protein concentrate

A trial of 218 days of duration was carried out to assess the use of pea protein concentrate (PPC) as a substitute for fish meal in diets for juvenile gilthead sea bream (52 g average initial weight), using four diets (0, 16, 32 and 48) with PPC inclusion levels of 0, 162, 325 and 487 g kg^?1, respectively. At the end of the trial, the fish reached weights of 397, 385, 383 and 355 g for 0, 16, 32 and 48 diets, respectively; diet 48 gave the lowest specific growth rate (SGR, 0.88% per day) but 0%, 16% and 32% PPC did not present statistical differences. Feed conversion ratio (FCR), protein efficiency ratio (PER) and body composition were not affected by the diets. Digestible protein retention was significantly higher with the 0% diet, but no energy retention differences were observed. Retention rates of ingested and digestible amino acids were very similar; in general, the retention of essential amino acids decreased as dietary PPC increased, and lysine retention was the highest and phenylalanine retention was the lowest. From the results of this experiment, it may be concluded that fish meal can be replaced up to 32% by PPC in sea bream without negative effects on fish weight gain, FCR and PER.     

Dietary inorganic phosphorus or microbial phytase supplementation improves growth,nutrient utilization and phosphorus mineralization of juvenile red sea bream,Pagrus major,fed soybean‐based diets

A 2 × 3 factorial design with triplicates examined the interaction between dietary inorganic phosphorus (IP) and phytase on growth, mineral utilization and phosphorus (P) mineralization in juvenile red sea bream. The treatments were three levels of dietary IP supplementation at 0, 2.5 and 5 g kg^?1, either without or with phytase supplementation [2000 FTU kg^?1; phytase unit is defined as the amount of enzyme activity which liberates 1 micromol of inorganic phosphorus per minute at pH 5.5 and 37 °C at a substrate concentration (sodium phytate) of 5.1 mmol L^?1]. Juvenile red sea bream (IBW = 1.3 g ± 0.1) were stocked twelve fish per tank and fed for 50 days. Growth and feed efficiency were significantly (P < 0.05) enhanced by both dietary P and phytase supplementation. Feed intake and survival rate were not significantly affected by the dietary treatments. Both dietary IP and phytase supplementation significantly increased plasma IP and Mg levels. Concentration of vertebral mineral and scale P was significantly increased by both dietary treatments. A skeletal malformation syndrome of scoliosis occurred in fish fed both non‐IP and non‐phytase supplemented diet. Interaction between main dietary effects was detected for vertebral Zn, scale P and whole‐body ash and Mg content. With regard to growth and other examined productivity traits, phosphorus requirement of juvenile red sea bream can be met if supplemented with 2000 FTU phytase kg^?1 or in the absence of phytase, by dietary inclusion of 2.5–5 g kg^?1 of IP.     

Plant protein and vegetable oil‐based diets modulate gilthead seabream (Sparus aurata) muscle biochemical status and proteolytic enzymes at an early postmortem stage

A 70 days feeding trial was carried out on juvenile gilthead seabream (Sparus aurata) (mean initial body weight: 362 ± 59 g) to evaluate whether the simultaneous replacement of fishmeal and fish oil by vegetable ingredients affected the muscle's proteolytic potential. Fish were fed either a fishmeal/fish oil diet, a fishmeal/vegetable oil diet, a plant protein/fish oil or a plant protein/vegetable oil diet. The use of dietary plant proteins resulted in lower sulphated glycosaminoglycans' content and lower glycogen phosphorylase activity in the muscle, while both plant proteins and vegetable oil increased muscle pH and reduced cathepsin B activity. Our results indicate that high replacement of fish meal and/or fish oil with plant ingredients has a significant impact on early postmortem metabolic processes and proteolytic potential of seabream muscle, especially when replacing both fish meal and fish oil.     

Effects of graded levels of minerals in a multi‐nutrient package on Gilthead sea bream (Sparus aurata) fed a plant‐based diet

Replacement of fish meal (FM) and oil (FO) by plant sources can alter the feed mineral profile. However, requirements of these nutrients have not been established for gilthead sea bream. The aim of the present study was to obtain information about the adequate levels of some of these minerals (such as Zn, Cu, Mn, Se, Co, Fe and Ca) in diets with low FM and FO levels. Six plant‐based practical diets were supplemented with increasing levels of a multi‐nutrient package for 155 days. Performance parameters, biochemical analyses of whole body, vertebrae, plasma and blood cells; haematocrit; expression of several genes in liver and vertebrae were conducted. Increasing multi‐nutrient package affected fish growth, expression of molecular markers and mineral content in different tissues. A regression method was used to establish a relation between multi‐nutrient package levels and different indicators. However, nutrient interactions made it difficult to obtain clear results and so specific effects of each mineral must be studied in more detail. Mineral supplementation was required for Zn, Cu, Mn, Se and Co, whilst basal levels of Ca were sufficient to cover the optimum levels. On the other hand, there is evidence regarding a possible interaction between Fe and Zn which reduced Fe availability and absorption.     

Effect of dietary phospholipid level on the development of gilthead sea bream (Sparus aurata) larvae fed a compound diet

The aim of the study was to determine the influence of dietary phospholipid (PL) levels on survival and development of first feeding gilthead sea bream (Sparus aurata) larvae. Larvae were fed from day 4 to 23 posthatching with an isoproteic and isolipidic formulated diet with graded levels of PL from 90–150 g kg^?1 dry matter (DM). A dietary PL content of more than 90 g kg^?1 DM seems to be necessary for sustaining growth of first feeding sea bream larvae. The survival rates of larvae fed the formulated diets (31–40% at day 23) were similar to those generally observed in marine aquaculture hatcheries with live prey feeding sequence. However, this high survival rate was not associated with high growth and the larvae showed, at the end of the study, a high proportion of individuals with abnormal liver and calculi in the urinary bladder. It is concluded that although the diets used here cannot be used in total replacement of live preys, they constitute a solid starting point for further nutritional studies with first feeding gilthead sea bream larvae.     

Optimum dietary soybean meal level for maximizing growth and nutrient utilization of on-growing gilthead sea bream (Sparus aurata)

Six isonitrogenous [450 g kg⁻¹ crude protein (CP)] and isoenergetic diets (23 kJ g⁻¹) with six levels of defatted soybean meal inclusion (0, 132, 263, 395, 526 and 658 g kg⁻¹) in substitution of fish meal were evaluated in gilthead sea bream of 242 g initial weight for 134 days. Fish fed diets S0, S13, S26 and S39 had a similar live weight (422, 422, 438 and 422 g, respectively) but fish fed diets S53 and S66 obtained the lowest final weight (385 and 333g, respectively), and similar results were presented in specific growth rate (SGR). Fish fed diets S53 and S66 also obtained the highest feed conversion ratio (FCR). Quadratic multiple regression equations were developed for SGR and FCR which were closely related to dietary soybean level. The optimum dietary soybean levels were 205 g kg⁻¹ for maximum SGR and 10 g kg⁻¹ for minimum FCR. Sensorial differences were appreciated by judges between fish fed S0 and S39 soybean level, but after a re-feeding period of 28 days with diet S0, these differences disappeared.     

Total nitrogen,carbon and phosphorus digestibility in gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fed with conventional and organic commercial feeds: implications for particulate waste production

Organic fish farming is postulated as a more environmentally friendly activity than conventional activities. However, environmental sustainability as regards waste output has not been addressed. In this respect, the most important environmental problems associated with fish farming are those related with the discharge of particulate wastes. In this study, total nitrogen, carbon and phosphorus digestibility was estimated in a wide size range of gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fed a commercially available conventional diet and an organic feed, as a previous step to assessing particulate waste output. Neither fish size nor feed nutrient content was seen to influence nutrient digestibility in either species. The organic diet provided higher carbon but lower nitrogen and phosphorus digestibility than conventional feed in both species. Simulations under real ongrowing conditions resulted in lower values for nitrogen and higher values for carbon particulate wastes when conventional feed was supplied to both species. Particulate phosphorus wastes were 2.6‐ to 3.4‐fold higher for fish fed the organic diet. Restrictions concerning NO the raw materials used for organic diet formulation and differences in nutrient bioavailability between the diets seemed to be the underlying reason for the differences found.     

Effect of dietary energy content on gilthead sea bream (Sparus aurata) feeding behaviour and nutritional use of the diet

We have studied how the diet energy level affects gilthead sea bream (Sparus aurata) daily pattern of demand‐feeding activity and nutritional use of the diet under summer‐ and winter‐like conditions. To that end, animals were kept in a closed circuit under controlled temperature and photoperiod, and fed one of two commercial diets with either high (H: 238 g kg^?1 fat) or low (L: 172 g kg^?1 fat) energy content. In summer conditions (26 °C; 12 : 12 L : D), both diets yielded similar growth rate (0.7 ± 0.0 and 0.7 ± 0.1) and thermal unit growth coefficient values (0.6 ± 0.0 and 0.6 ± 0.0), and although the daily rate of delivered feed was somewhat higher for fish under the high‐energy diet (16 ± 2 g kg^?1 of fish) the difference was not significant. In winter conditions (17 °C; 9 : 15 L : D), on the other hand, no differences were found for any of the parameters evaluated. Thus, the higher lipid content of the diet does not appear to have any protein sparing effect. The ‘summer’ demand‐feeding pattern displayed three daily peaks, which were quite apparent for fish under the low‐energy diet, but rather smoothed for those that ate the energy‐rich diet. This profile was replaced in winter conditions by a single peak around noon, and the animals also displayed a lower overall number of demands.     

Phytase and sodium diformate supplementation in a plant‐based diet improves protein and mineral utilization in rainbow trout (Oncorhynchus mykiss)

A basal isonitrogenous and isoenergetic plant‐based diet (Control) was supplemented with either 10 g kg^?1 sodium diformate (NaDF), 4000 FTU kg^?1 phytase (Phy) or a combination of both additives (NaDF + Phy). Three hundred juvenile rainbow trout with an average weight of 120 g were randomly distributed into 12 fibreglass tanks (300 L). After 65 days of trial, fish fed diets containing phytase, NaDF or the combination of both additives showed a higher growth rate (P < 0.05) compared to fish fed Control diet. NaDF increased feed intake (P = 0.032), while phytase inclusion resulted in a better feed conversion ratio (P < 0.0001) and a higher N retention efficiency (P = 0.02) compared with the Control. Apparent digestibility of P, Ca, Mg and Zn was improved by the use of phytase (P < 0.005) as well as P, Ca and Mg retention efficiency in fish (P < 0.0001). Using 4000 FTU kg^?1 phytase in plant‐based diets resulted in a 13% and 50% reduction in N and P loadings, respectively. The use of NaDF in combination with phytase in a plant‐based diet for rainbow trout resulted in a higher weight gain than that when NaDF was used alone.