J. Socorro

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.

Recent advances in lipid nutrition in fish larvae

Due to the importance of dietary lipid utilization for larval rearing success, increasing attention has been paid during the last years to different aspects of larval lipid nutrition such as digestion, absorption, transport and metabolism, which are frequently studied by different research groups. The present study reviews the published information on these aspects, including some recent results obtained in our laboratory, that contribute to a better understanding of larval lipid nutrition.Neutral lipase activity was found in the digesta of larval gilthead seabream as early as first feeding, followed by a significant increase which reached up 8 times the initial levels at day 15 and was clearly influenced by the fatty acid composition of dietary lipids. Accordingly, the capacity for lipid absorption by the intestinal epithelium has been also observed at the onset of exogenous feeding, although the specific location in the different digestive tract segments differ with species. Whereas the capacity to absorb lipid increases with development in live prey-fed larvae, this improvemment is delayed in larvae fed formulated diet. Increasing dietary phosphatidyl cholines levels enhanced lipid absorption regardless of whether it is of soybean or marine origin, but the latter improved hepatic lipid utilization. Enzymatic, histological and biochemical evidences suggest that marine fish larvae are able to effectively digest and absorb n-3 HUFA-rich triacylglycerols, but feeding with phosphoacylglycerols, particularly if they are rich in n-3 HUFA, would enhance phosphoacylglycerols digestion and specially lipid transport alowing a better n-3 HUFA incorporation into larval membrane lipids and promoting fish growth. Although the essentiality of n-3 HUFA for larval marine fish has been studied extensively, only recently has the importance of dietary arachidonic acid in the larvae of few species been recognised. Evidences for competitive interactions among these essential fatty acids suggest that besides a minimum dietary requirement for each essential fatty acid, their relative ratios must also be considered.

Corn gluten and meat and bone meals as protein sources in diets for gilthead seabream (Sparus aurata): Nutritional and histological implications

Abstract Two experiments were conducted to compare the effect of the partial substitution of fish meal by two different protein sources, corn gluten (CGM) and meat and bone meals (MBM) in diets for juveniles gilthead seabream. Growth, feed efficiency, protein efficiency ratio and protein productive values were not significantly affected by the source of dietary protein, although higher values were observed with diets containing increasing levels of meat and bone meal. No differences were found in fish proximate composition at the end of the experiment. Histological studies of liver tissue showed no liver alteration in fish fed diets including increasing levels of corn gluten meal. On the contrary, an increased deposition of lipids, nuclei polarization and isolated necrotic focus were found in hepatocites of fish fed diets exceeding 20% of meat and bone protein. Apparent protein digestibility (ADC) in diets containing CGM showed similar results to those obtained with the control diet. However, a significant reduction in digestibility was observed when MBM was used as partial substitute of fish meal protein. A negative correlation between dietary ash content and protein digestibility was observed. Higher amounts of nitrogen were excreted as levels of CGM and MBM increased in the diets, being significantly higher in the case of 40% substitution either with CGM or MBM protein.

Combined effect of lipid level and fish meal quality on liver histology of gilthead seabream /Sparus aurata

Abstract Effect of eight diets comparing three different lipid levels (15, 22 and 27%) and two fish meal qualities were studied on growth and liver histology. Fish meal quality was judged by the content of biogenic amines and temperature processing techniques. The experiment included a comparison of pelleted feed with extruded feed for the 22% lipid diet. A total of 1140 gilthead seabream of 70 g average initial body weight were randomly stocked in 500-l fiberglass tanks in duplicate groups of 60 fish. After 2 months of experiment, the fish were transferred to 1-m3 tanks. Fish were fed twice a day to apparent satiation for 6 months until they reached about 400 g (commercial size). Fish fed diets containing high quality fish meal showed, in general, a higher growth than those fish fed with low quality fish meal. For diets containing high quality fish meal, the fish fed 22 and 27% dietary lipid had significantly higher growth than those fish fed 15% dietary lipid. On the contrary, in diets containing low quality fish meal, only fish fed 27% dietary lipid showed significantly the higher growth rate. Fish fed the pelletized diets showed a lower growth than those fish fed extruded diets. Livers from fish fed diets containing high quality fish meal and 27% lipid showed foci of swelling hepatocytes that were not found for low quality fish meal at the same dietary lipid content. Ultrastructurally, these foci were characterized to present irregular nuclei displaced to periphery of hepatocytes and large lipid droplets in the cytoplasm. Livers from fish fed high and low fish meal qualities with 22% lipid showed similar morphological characters of hepatocytes to those that fed 15% lipid, but the difference was observed in the nuclei displacement.

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.

Increase of the dietary n - 3/n - 6 fatty acid ratio and addition of phosphorus improves liver histological alterations induced by feeding diets containing soybean meal to gilthead seabream, Sparus aurata

Abstract In a previous study, several histological alterations were found in the liver of gilthead seabream fed with a diet containing 30% soybean meal (SBM). In the current study, SBM containing diets were supplemented with either potassium phosphate, zinc sulfate or phytase ( Aspergillus ficuum ), or increasing the dietary n −3/ n −6 fatty acids ratio to meet that of a fish meal based diet. Diet composition did not affect fish growth, feed efficiency (FE) or protein productive value (PER). Phosphorous supplementation significantly reduced hepatosomatic indexes (HSI), although it did not alter liver lipid content. Both phosphorous supplementation and correcting the dietary n −3/ n −6 fatty acid ratio significantly altered the lipid and protein content in fish muscle. Only these two treatments and principally the corrected dietary n −3/ n −6 fatty acid ratio, improved the liver histological alterations observed in fish fed with SBM based diets.

Dietary and culture influences on macrophage aggregate parameters in gilthead seabream (Sparus aurata) juveniles

Abstract Macrophage aggregates (MAs) are structures in the spleen, kidney and sometimes liver of fishes which have various functions such as recycling/storing/detoxification of cellular wastes and exogenous substances. They have been also reported to be important in the specific immune response and are used as health indicators. Changes in MA density, size and pigment content have been used in national and local monitoring programs in the U.S. as indicators of contaminant exposure. However, MA number and structure can also be affected by other factors, including general stress or nutritional status of fish. An experiment was conducted to study the effects of vitamin E and n −3 highly unsaturated fatty acid (HUFA) deficiencies and stocking density on spleen and kidney MAs of gilthead seabream, one of the most important species for Mediterranean aquaculture. Fish were held at two stocking densities, high and low, and fed experimental diets. Diet NE had no supplemental vitamin E, Diet NFA was deficient in n −3 HUFA and Diet C was a control diet. Number, size and shape factor of MAs were measured using image analysis. The percentage of tissue occupied by MAs was calculated from these measurements. The results showed that high stocking density alone increased the number of splenic but not kidney MAs of fish fed the control diet. A deficiency of n −3 HUFA alone also increased the number of splenic but not kidney MAs at both stocking densities. Vitamin E deficiency alone had no significant effect on MAs in either organ. However, the combined effect of vitamin E deficiency and high stocking density increased the number and size of kidney but not splenic MAs. This study indicates that specific dietary deficiencies can influence MA accumulation and that splenic MAs may be more responsive to general stress than kidney MAs.

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.

Occurrence of skeletal deformities and osteological development in red porgy Pagrus pagrus larvae cultured under different rearing techniques

The present study describes the osteological development and the occurrence of skeletal deformities in red porgy Pagrus pagrus larvae in relation to the intensification of the rearing system. Eggs obtained from natural spawning were cultured under two different rearing systems: intensive (100 eggs l⁻¹) in 2000 l and semi-intensive (mesocosm) system (5 eggs l⁻¹) in 40,000 l conico-cylindrical tanks. Fish samples were periodically collected along the development from hatching to juveniles at 95 days post hatching (dph). Osteological development, meristic counts and the presence of skeletal deformities were evaluated. Despite the external appearance of the juveniles being similar to wild standards, X-ray studies revealed a high number of fish (semi-intensive: 37·8%; intensive: 45·5%) with skeletal deformities. Regardless of the rearing system, no significant interaction was found between the per cent of the most common deformities, axial deviations (lordosis and presence of fused vertebrae). Cranial deformities and kyphosis incidences, however, were significantly higher in intensively cultured P. pagrus. Also, the fused vertebrae in these fish were located mainly in the caudal area instead of pre-haemal area for semi-intensively reared P. pagrus. Moreover, a significant interaction was found between the total number of vertebrae and the type of rearing system used; fish from the intensive system showing a higher number of fish with an extra vertebrae (10 abdominal + 15 caudal). Present results suggest a relationship among feeding sequence, osteological development and deformity incidence and location in P. pagrus larvae.

First records of Hippocampus algiricus in the Canary Islands (north-east Atlantic Ocean) with an observation of hybridization with Hippocampus hippocampus.

Morphometric and genetic analyses confirmed the first records of the West African seahorse Hippocampus algiricus at Gran Canaria Island (north-east Atlantic Ocean), and also the first evidence of interspecific hybridization in seahorses. These results provide additional data on the distribution of H. algiricus that may help to establish future conservation strategies, and uncover a new potential sympatric scenario between H. algiricus and Hippocampus hippocampus.