H. Fernandez-Palacios

Effect of broodstock nutrition on reproductive performance of fish

Abstract In many cultured fish species, particularly in those new for aquaculture, unpredictable and variable reproductive performance is an important limiting factor for the successful mass production of juveniles. An improvement in broodstock nutrition and feeding has been shown to greatly improve not only egg and sperm quality but also seed production. Gonadal development and fecundity are affected by certain essential dietary nutrients, especially in continuous spawners with short vitellogenic periods. Thus, during the last two decades, more attention has been paid to the level of different nutrients in broodstock diets. However, studies on broodstock nutrition are limited and relatively expensive to conduct. Lipid and fatty acid composition of broodstock diet have been identified as major dietary factors that determine successful reproduction and survival of offspring. Some fish species readily incorporate dietary unsaturated fatty acids into eggs, even during the course of the spawning season. Highly unsaturated fatty acids (HUFA) with 20 or more carbon atoms affect, directly or through their metabolites, fish maturation and steroidogenesis. In some species, HUFA in broodstock diets increases fecundity, fertilization and egg quality. As in higher vertebrates, vitamin E deficiency affects reproductive performance, causing immature gonads and lower hatching rate and survival of offspring. For example, elevation of dietary α-tocopherol levels has been found to reduce the percentage of abnormal eggs and increase fecundity in the gilthead seabream ( Sparus aurata ). Ascorbic acid has also been shown to play an important role in salmonid reproduction, where the dietary requirement of broodstock was higher than that of juveniles. Among different feed ingredients, cuttlefish, squid and krill meals are recognized as valuable components of broodstock diets. The protein component of cuttlefish and squid together with their optimal concentration of HUFA appear to be responsible for their positive effect on reproductive performance. Both polar and nonpolar lipid fractions of raw krill were found to effectively improve egg quality.

Soybean and lupin seed meals as protein sources in diets for gilthead seabream (Sparus aurata) : nutritional and histological implications

The use of vegetable protein sources in diets for freshwater fish has been studied in more detail than for marine fish species. Two experiments were conducted to compare the effect of the partial substitution of fish meal by two different vegetable protein sources, soybean and lupin seed meals. Mean feed intake and growth were not significantly influenced by type or level of plant protein in the diet. Feed utilization indexes such as feed efficiency, protein efficiency ratio and protein productive values were not significantly affected by the type of plant protein in the diet, although a general reduction of these values was observed with increased inclusion of soybean meal. Histological studies showed an increased deposition of lipid and decreased glycogen deposits in the liver with increased levels of dietary soybean meal. Protein digestibility coefficients for lupin seed meal diets were similar to the control and 10% higher than those for the soybean meal diets. A significant reduction in trypsin activity was observed in fish fed the lupin seed meal diets, and for soybean meal diets when the substitution level reached 30%. Diets including plant protein showed a higher peak of ammonia excretion rate, which appeared 2 h later than that of the fish meal diet. Highest values of dissolved ammonia were registered in fish fed a soybean meal-based diet. These results suggest that properly treated lupin meals could be an important alternative dietary protein source for gilthead seabream.

Effect of n − 3 HUFA level in broodstock diets on egg quality of gilthead sea bream (Sparus aurata L.)

Abstract A variety of morphological, biological and biochemical parameters of freshly spawned eggs of gilthead seabream ( Sparus aurata L.) were studied to determine the optimum n − 3 HUFA level in broodstock diets necessary to obtain a high-quality spawn. The effect of very high dietary n − 3 HUFA levels on fish reproduction was also investigated. Broodstock were separated into 8 groups and fed four diets containing different levels of n − 3 HUFA, ranging from 1.13 to 3.15%, for 3 months. Spawning and egg qualities were evaluated daily by 7 parameters. Besides, 8 samples of eggs were taken during the experimental period and were analyzed for proximate and fatty acid composition. After 3 weeks of feeding, significantly improved spawning quality in the broodstock fed 1.6% n − 3 HUFA was observed in terms of fecundity, hatching and larval survival. Unfertilized egg rates were significantly reduced by the increase in dietary 20:5n − 3. The highest level of dietary n − 3 HUFA was associated with a decreased fecundity and yolk sac hypertrophy in just hatched out larvae, n − 3 HUFA content in the eggs showed a positive correlation with dietary n − 3 HUFA, mainly due to the change in 20:5n − 3 content of the eggs.

Effect of dietary arachidonic acid levels on growth and survival of gilthead sea bream /Sparus aurata L. larvae

In order to determine the effect of different levels of arachidonic acid (AA) in microdiets on growth and survival of gilthead seabream larvae, two experiments were carried out. In the first experiment, 17-day old larvae were fed microdiets for 14 days. In this trial, we tested four diets with a similar docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio and AA in the range of 0.1%–1.8% dry weight (d.w.) and a fifth diet with 1.0% d.w. of AA and a different DHA/EPA ratio. In the second experiment, 16-day old larvae were fed for 21 days on two microdiets with levels of 0.1% and 1.0% d.w. AA. All diets in the two experiments had the same total n−3 HUFA level. Growth was measured by total length and dry body weight of larvae. Larval lipids were extracted and fatty acid compositions of total neutral lipid (NL) and total polar lipid (PL) fractions were determined by gas chromatography. In the first experiment, the diet containing 1.8% d.w. of AA showed the best survival (P<0.05) but did not improve growth rate. In the second experiment, an increase in the AA dietary level from 0.1% to 1.0% d.w. significantly improved (P<0.05) larval growth. EPA accumulation in the PLs of the larvae was negatively affected by the inclusion of dietary AA. When working with a fixed dietary n−3 HUFA level (2.2% d.w.), the effect of dietary AA on larval growth was masked by that of the dietary DHA/EPA ratio. However, when DHA/EPA ratio in diet was unchanged (∼1.8), it was possible to improve larval growth by supplementing the diet with 1.0 d.w. of AA. The negative effect produced by the increment of dietary AA on the EPA incorporation into the larval PLs may be related to a competition interaction.

Effect of different dietary polar lipid levels and different n−3 HUFA content in polar lipids on gut and liver histological structure of gilthead seabream (Sparus aurata) larvae

Abstract In a previous study feeding larval gilthead seabream on microdiets, an improved growth rate was observed when dietary n−3 HUFA (n−3 highly unsaturated fatty acids) were contained in the polar lipid fraction. A beneficial effect of dietary lecithin on n−3 HUFA incorporation to the larval polar lipids was also observed. To confirm those results and in order to obtain additional information on larval gut and liver histological structure, 11-day-old larvae were fed 4 microdiets differing in lipid composition. In diets N′ and NL′, the main sources of n−3 HUFA were neutral lipids, and polar lipids in diets P′ and PL′. Three lecithin levels were tested, being the highest in diet NL′ and the lowest in diet P′. The total n−3 HUFA level in diets N′ and NL′ was enough to meet the essential fatty acid requirement of larval gilthead seabream obtained in a previous study with a triacylglyceride based diet, while diets P′ and PL′ had a total n−3 HUFA level lower than the minimum determined. A reduction in the larval essential fatty acid requirement to 1.5% d.w. was obtained by feeding dietary n−3 HUFA present in the polar lipid fraction. Feeding larvae with microdiets with low polar lipid levels produced an accumulation of lipid droplets in the enterocytes and a high number of lipid vacuoles in the hepatocytes producing nuclear migration and suggesting a need of dietary polar lipid for lipid transport.

The effect of dietary protein and lipid from squid and fish meals on egg quality of broodstock for gilthead seabream (Sparus aurata)

Abstract To investigate the specific component of squid meal which enhances spawning quality, gilthead seabream broodstock were fed four isonitrogenous, isolipidic and isocaloric diets containing fat-soluble or fat-insoluble extracts from fish and squid meals for 2 months during the spawning season. A positive effect of the fat-insoluble fraction of squid meal was observed on the total number of eggs, egg viability and the number of larvae produced daily per kilogram of female. Increased dietary levels of eicosapentaenoic acid correlated with the number of fertilized eggs produced, whereas elevation of n − 3 highly unsaturated fatty acid levels was correlated with a reduction in the percentage of eggs with more than one lipid droplet. The results of this study highlight the value of squid meal as a good protein and lipid source in diets for gilthead seabream broodstock.

Development of red porgy Pagrus pagrus visual system in relation with changes in the digestive tract and larval feeding habits

Abstract Red porgy larvae, like other sparids such as red seabream are visual feeders. The normal development of the visual system is essential for successful prey capture and predator avoidance, leading to increased larval growth and survival. The aim of this work is to characterise the development of visual organs in relation to changes in the digestive system and feeding habits. Twenty-five larvae from hatching to day 29 were daily collected from the rearing tank, fixed in formalin, embedded in paraffin, 5 μm sectioned and stained with haematoxylin and eosin (H&E) and Periodic Acid Shift Reactive-Haematoxiline (PAS-Hx). Light microscopy was used to study changes in ocular morphology with respect to digestive system development. At hatching, eye and digestive systems of Pagrus pagrus larvae have no function. However, at day 3 post-hatch, when the mouth opens, the larvae must be ready for prey capture and digestion. Despite this, few day 3 larvae had food in the digestive tract. At day 4 photoreceptors were well developed in the eye, pigmentation pattern was complete and thus the visual system was completely ready for prey capture. This development coincided with detection of digestive activity in the midgut and most of larvae starting to take food. The results of this study suggest that adequate development of the visual system is important to establish the start of exogenous feeding. Besides, the appearance of rod cells increases larval photosensitivity and suggests that changes in lighting regimes could be necessary throughout the larval phase.

Effect of lipid and n−3 HUFA levels in microdiets on growth, survival and fatty acid composition of larval gilthead seabream (Sparus aurata)

Abstract The results of studies on the essential fatty acid requirement of larval gilthead seabream differ in the recommended n −3 HUFA levels in rotifers ( Brachionus plicatilis ) necessary to obtain optimal larval growth and survival. Some authors have suggested that the total lipid content of the rotifers may influence the fatty acid requirement of the larvae. In order to study this hypothesis, an experiment was conducted by feeding gilthead seabream larvae microdiets containing combinations of two lipid and two essential fatty acid levels. Fifteen-day-old gilthead seabream larvae were fed with 4 microparticulated diets containing the following lipid and n −3 HUFA levels: (A) 12.44% and 0.82%; (B) 12.72% and 2.16%; (C) 19.45% and 0.74%; and (D) 20.03% and 2.05%. Larvae were fed the experimental diets together with a small amount of rotifers cultured on bakers yeast for 12 days. Larvae fed Diet A had the lowest growth rate ( P n −3 HUFA (B and D) supported the best survival rates regardless of their lipid content. These results showed that for the lipid levels tested, the larval n −3 HUFA requirement did not decrease as the lipid level in the diet decreased.

Rearing techniques for red porgy Pagrus pagrus during larval development

Red porgy can be considered as a potential candidate to diversify aquaculture production of sparids, due both to the importance of red porgy fisheries and market within Europe, and to its phylogenetic closeness to gilthead seabream. Spontaneously spawned eggs were obtained from a broodstock of wild individuals captured in Canarian waters. Different rearing trials were conducted to study the success of: (a) different egg stocking densities (100, 150 and 200 eggs/l); (b) first feeding with rotifers enriched with different products (Powersh-fish oil, freeze-dried shark eggs and Selco supplemented with Nannochloropsis sp); and (c) supply of rotifers to larval cultures at different concentrations (5, 7 and 10 rotifers/ml). In all cases, larval feeding lasted for 14 days. Larval length was measured at the time of mouth opening, at day 10 of life, and at the end of the experiments. Larval survival was estimated at the end of each experiment by counting all the remaining live larvae. Total lipid and fatty acid composition of rotifers and larvae were analyzed and discussed in relation to larval growth and survival. In this study, egg densities between 100 and 150 eggs/l and the use of rotifers enriched with Powersh-W, containing a high level of 22:6n−3, at concentrations of 5–7 rotifers/ml produced the best larval growth and survival.

First studies on spawning, embryonic and larval development of Dentex gibbosus (Rafinesque, 1810) (Osteichthyes, Sparidae) under controlled conditions

Abstract Pink dentex ( D. gibbosus ) can be considered as a potential candidate to diversify the culture of Sparidae, due both to the importance of dentex fisheries and market within Europe, and to its phylogenetic closeness to the gilthead sea bream ( Sparus aurata , Linnaeus, 1758). First trials to obtain D. gibbosus spawnings under captive conditions were carried out at the Planta Experimental de Cultivos Marinos (Instituto Canario de Ciencias Marinas, Gran Canaria, Canary Islands, Spain) in May, 1991. Broodstock management conditions determining egg quality, embryonic and larval development of D. gibbosus up to day 31 are described for the first time. Larval allometric characteristics were studied. The equation y =2.321×e 0.03975 x represents larval growth under experimental conditions. A comparison of egg size, hatching time and size of newly hatched larvae in several Sparidae under culture conditions is also presented. Results on broodstock acclimation, natural spawnings and larval growth rates suggest that pink dentex has a high potential for commercial culture.