Sea Bream Larvae Research Articles

Optimum krill phospholipids content in microdiets for gilthead seabream (Sparus aurata) larvae

The aim of the present study was to determine the optimum dietary levels of krill phospholipids (KPL) for sea bream (Sparus aurata) larvae, and its influence on larval development and digestive enzymes activity. Larvae were fed five formulated microdiets with five different levels of KPL. Complete replacement of live preys with the experimental microdiets for seabream larvae produced high survival and growth rates, particularly in fish fed the highest levels of KPL. In the present study, increase in dietary KPL up to 120 g kg−1 (100 g kg−1 total PL) significantly improved larval survival and growth, whereas further increase did not improve those parameters. An increase in alkaline phosphatase, trypsin and lipase activity with the elevation of KPL up to 120 g kg−1 was also found denoting a better functioning of digestive system. Besides, there was a linear substrate stimulatory effect of dietary KPL on phospholipase A2 activity. Finally, increasing dietary KPL lead to better assimilation of n-3 HUFA especially eicosapentaenoic acid, reflected in the higher content of these fatty acids in both neutral and polar lipids of the larvae. In summary, KPL were found to be an excellent source of lipids for seabream larvae. Optimum inclusion levels of this ingredient in microdiets to completely substitute live preys at this larval age were found to be 120 g kg−1 KPL.

Fish oil replacement by different microalgal products in microdiets for early weaning of gilthead sea bream (Sparus aurata, L.)

The aim of this study was to determine if algal products rich in DHA or ARA are able to completely replace fish oil in microdiets for marine fish larvae, gilthead seabream and if extra supplementation with EPA may further enhance larval performance. For that purpose, 20 day-old gilthead seabream larvae of 5.97 ± 0.4 mm mean total length and 0.12 ± 0.001 mg mean dry body weight were fed with five microdiets tested by triplicate: a control diet based on sardine oil; a diet containing AquaGrow® DHA (diet DHA) to completely substitute the sardine oil; a diet containing AquaGrow® ARA (diet ARA); a diet containing both products, AquaGrow® DHA and AquaGrow® ARA to completely substitute the fish oil; and, a diet containing both products, AquaGrow® DHA and AquaGrow® ARA, together with an EPA source. Temperature, air and salinity activity tests were also performed to detect larval resistance to stress. At the end of the experiment, final survivals did not differ among groups. The microorganism produced DHA was able to completely replace fish oil in weaning diets for gilthead seabream without affecting survival, growth or stress resistance, whereas the inclusion of microorganism produced ARA did not improve larval performance. Moreover, addition of EPA to diets with total replacement of fish oil by microorganism produced DHA and ARA, significantly improved growth in terms of body weight and total length. The results of this study denoted the good nutritional value of microorganisms produced DHA as a replacement of fish oil in weaning diets for gilthead seabream, without a complementary addition of ARA. However, dietary supplementation of EPA seems to be necessary to further promote larval performance.

Supplementations of dl‐Methionine and Methionine Dipeptide in Diets are Effective for the Development and Growth of Larvae and Juvenile Red Sea Bream, Pagrus major

Growth trials for larvae and juvenile red sea bream, Pagrus major, were conducted to elucidate the efficacy of two molecular forms of methionine; dl‐methionine (dl‐Met) and methionine dipeptide (Met‐Met). For the larvae experiment, five experimental diets were formulated and fed to fish (42 mg) for 30 days. A diet which has 15% soy protein isolate served as the control diet. Similarly, test diets supplemented with dl‐Met and Met‐Met at 0.5%, which were either precoated by zein or intact, were also formulated. For the juvenile experiment, five experimental diets were formulated wherein the control diet contained 25% soy protein isolate. Test diets were supplemented with dl‐Met and Met‐Met at 0.75%, which were either coated by carboxymethycellulose or intact and fed to juveniles (0.75 g) for 56 days. The results of two feeding trials showed both dl‐Met and Met‐Met can be equally utilized by red sea bream larvae and juveniles. Coating the amino acid significantly improved both fish larval and juvenile growth performance. The development of digestive protease activity of larvae was significantly influenced by coating the amino acid, but the type of methionine was not a factor in changing the protease activity of larvae.

Impact of dietary protein hydrolysates on skeleton quality and proteome in Diplodus sargus larvae

In order to investigate the effects of dietary protein hydrolysates (PH) on larval growth performance, skeleton quality and proteome expression, triplicate groups of white seabream (Diplodus sargus) larvae were co-fed from first-feeding with live feed and three microencapsulated diets differing in the molecular weight of their PH fraction (Control – inclusion of CPSP-90; H – inclusion of a high amount in 0.5–30 kDa hydrolysates; L – inclusion of a high amount in <0.5 kDa hydrolysates). At 15 days after hatching (DAH), proteome expression changes were assessed in entire larvae by two-dimensional gel electrophoresis and the quality of larval skeleton was analysed at 28 DAH through double staining of cartilage and bone. Dietary PH fractions tested affected growth, the larvae fed diet L being significantly larger than those fed diet H, but it did not affect the incidence of deformed larvae, nor the number of deformities per fish. Two-dimensional analysis of larvae proteome allowed the detection and the comparative quantification of a total of 709 protein spots having a pI between 4 and 7, around half of which had an expression significantly affected by dietary treatment, the main difference being between proteome of Control larvae with those of both groups L and H. From these spots, 52 proteins involved in diverse processes such as cytoskeletal dynamics, energetic, lipoprotein, amino acid (AA), and nucleotide metabolisms, protein chaperoning and degradation, and signal transduction, were identified. This study revealed that the molecular weight of the dietary protein hydrolysate fraction had a minor impact on skeletal deformities in white seabream larvae, but affected growth performance and had a strong impact on larvae whole body proteome.

Artemia 공급 단계에서 은어(Plecoglossus altivelis), 조피볼락(Sebastes schlegeli ), 감성돔(Acanthopagrus schlegeli ) 및 넙치(Paralichthys olivaeus)의 소화효소 활성

We compared the nutritional requirements of whole larvae of the black seabream Acanthopagrus schlegeli, sweet fish Plecoglossus altivelis, olive flounder Paralichthys olivaeus and rock fish Sebastes schlegeli. The larvae were 20, 30, 14 and 5 DAH (or spawning) of black seabream, sweet fish, olive flounder and rock fish, respectively. Specific <TEX>${\alpha}$</TEX>-amylase activity (mU/mg protein) was highest (8,324.9 mU/mg protein) in rock fish larvae (P<0.05). Specific trypsin-like protease activity was highest (11,330.1 mU/mg protein) in black seabream larvae (P<0.05), which also exhibited the highest activity, 685.5 mU/mg dry weight (P<0.05). The specific activities per mg protein and mg dry weight of black seabream were the highest (187.4 mU/mg protein and 11.3 mU/mg dry weight, respectively) (P<0.05). A/P, P/L and A/L ratios of rock fish were 1.47, 90.3 and 133.1, respectively (P<0.05). We present here basic larval digestive enzymatic nutritional requirement data.

Protein hydrolysates from yeast and pig blood as alternative raw materials in microdiets for gilthead sea bream (Sparus aurata) larvae

In this study, we have evaluated the incorporation of two types of protein hydrolysates at 9 and 12% levels of inclusion, one from yeast (Saccharomyces cerevisiae, YPH) and another one from pig blood (PBPH), in microdiets for gilthead sea bream (Sparus aurata) larvae, and compared these results to a microdiet containing fish protein hydrolysate and another group only fed with enriched live prey (rotifers and Artemia). The trial consisted in substituting up to 75% (wt/wt) the enriched Artemia with the experimental microdiets from 15 to 40days post-hatch, whereas larvae were exclusively fed on microdiets from 40 to 55dph. Protein hydrolysates used in the present study were obtained from different raw materials (yeast, pig blood and fish protein concentrate) and differed in their amino acid (AA) profile and in their molecular weight distribution. YPH and PBPH were mainly composed by free amino acids (FAA) (44%, MW<200Da), di- and tripeptides (50%, 200<MW<500Da) and 6% of larger polypeptides (500<MW<2500Da); whereas the fish protein hydrolysate (FPH) did only contain a minor quantity of FAA (1.5%) and was mainly composed of di- and tripeptides (36.5%) and larger polypeptides (51.4%, 500<MW<2500Da). The contents in FAA and di- and tripeptides in the microdiet containing FPH were 0.2 and 4.4%, respectively. FAA levels in microdiets including YPH and PBPH at 9 and 12% were 4.0 and 5.3%, whereas levels of di- and tripeptides were 4.5 and 6.0%, respectively. Results revealed that FPH in microdiets for marine fish larvae may be replaced by alternative protein hydrolysates obtained from yeast and pig blood, as fish fed with those diets performed, in terms of growth, survival, level of maturation of the enterocytes (activity of cytosolic and brush border enzymes) and incidence of skeletal deformities, as well as those larvae fed with only enriched live preys (rotifers and Artemia). Using YPH and PBPH, the inclusion level of protein hydrolysate in microdiets might be reduced to 9% (3% lesser to actual practices using fish protein hydrolysates) without affecting larval performance. Present results suggested the importance of leucine, valine and phenylalanine in fish larval skeletogenesis and in the appearance of skeletal disorders.

Morphological Development and Allometric Growth of Sharpsnout Seabream (Diplodus puntazzo) Larvae

In this study, morphological development and allometric growth were investigated in the sharpsnout seabream, Diplodus puntazzo, during larval development until the end of the weaning on day 42. Average total length (TL) of newly hatched larvae was 2.91±0.11 mm and it was 3.35±0.13 mm TL at the onset of feeding at 4 days after hatching (DAH). Initial swimbladder inflation occurred at 10 DAH (5.11±0.45 mm TL) and post-inflation became more elongate at 15 DAH (5.95±0.43 mm TL). The notochord flexion occurred between 5.95±0.43 mm TL at 15 DAH and 7.98±0.72 mm TL on 24 DAH. At the end of weaning, larvae were 16.03±1.74 mm TL at 42 DAH. The majority of all allometric changes from inflection point were integrated with the larval and the metamorphosis stage. Inflections in body proportion changes occurred mainly at 5.12, 5.95 and 7.98 mm TL, corresponding to initial swimbladder inflation and flexion period of notochord, respectively.

Effects of Feeding Enriched Artemia Fransiscana with HUFA, Vitamin C and E on Growth Performance, Survival and Stress Resistance of Yellowfin Seabream Larvae

Effects of feeding highly unsaturated fatty acid (HUFA), vitamins E and C enriched Artemia fransiscana nauplii on growth, survival and stress resistance of yellowfin seabream, A. latus were investigated. Larvae at first exogenous feeding with 53 ± 5 mg body weight were fed with HUFA+5%, 10% and 15% vitamin C-enriched Artemiai (C1, C2 and C3 groups, respectively), HUFA+5% and 10% vitamin E-enriched Artemia (E1 and E2 groups, respectively), HUFA+2.5% (W/W) vitamin C and E enriched Artemia (CE2 group), HUFA+5% (W/W) vitamin C and E-enriched Artemia (CE1 group), HUFA without vitamin (HUFA group) and non-enriched Artemia (control) in 3 replicates. Enriched Artemia feeding for all treatments was initialized on day 17 and finished on day 23 post hatch. After the period of enrichment, the larvae were fed with Coppens diet from day 23 to 36 and then, the sampling was done. Larvae resistance to osmotic and temperature stresses was performed with submersion in fresh water (0.5-1 ppt) and cold water (15°C) for 1h, respectively. Larvae growth factors except for DGR were not significantly different between the groups (p>0.05). Fish fed non-enriched Artemia had significantly higher DGR (0.63 ± 0.04) (p<0.05). Mortality rate was significantly different between control and other groups from day 17 (p<0.05). Stress tolerance, cortisol and total protein were not significantly different among the groups. Glucose was only significantly different between C3 and CE2. Results indicate that enrichment of Artemia fransiscana with HUFA and vitamins E and C increases survival in yellowfin seabream larvae at its first feeding.

Teleost fish larvae adapt to dietary arachidonic acid supply through modulation of the expression of lipid metabolism and stress response genes

Dietary fatty acid supply can affect stress response in fish during early development. Although knowledge on the mechanisms involved in fatty acid regulation of stress tolerance is scarce, it has often been hypothesised that eicosanoid profiles can influence cortisol production. Genomic cortisol actions are mediated by cytosolic receptors which may respond to cellular fatty acid signalling. An experiment was designed to test the effects of feeding gilthead sea-bream larvae with four microdiets, containing graded arachidonic acid (ARA) levels (0·4, 0·8, 1·5 and 3·0%), on the expression of genes involved in stress response (steroidogenic acute regulatory protein, glucocorticoid receptor and phosphoenolpyruvate carboxykinase), lipid and, particularly, eicosanoid metabolism (hormone-sensitive lipase, PPARα, phospholipase A2, cyclo-oxygenase-2 and 5-lipoxygenase), as determined by real-time quantitative PCR. Fish fatty acid phenotypes reflected dietary fatty acid profiles. Growth performance, survival after acute stress and similar whole-body basal cortisol levels suggested that sea-bream larvae could tolerate a wide range of dietary ARA levels. Transcription of all genes analysed was significantly reduced at dietary ARA levels above 0·4%. Nonetheless, despite practical suppression of phospholipase A2 transcription, higher leukotriene B4 levels were detected in larvae fed 3·0% ARA, whereas a similar trend was observed regarding PGE2 production. The present study demonstrates that adaptation to a wide range of dietary ARA levels in gilthead sea-bream larvae involves the modulation of the expression of genes related to eicosanoid synthesis, lipid metabolism and stress response. The roles of ARA, other polyunsaturates and eicosanoids as signals in this process are discussed.

Ontogeny of gene expression of group IB phospholipase A 2 isoforms in the red sea bream, Pagrus ( Chrysophrys) major

The red sea bream ( Pagrus major) was previously found to express mRNAs for two group IB phospholipase A 2 (PLA 2) isoforms, DE-1 and DE-2, in the digestive organs, including the hepatopancreas, pyloric caeca, and intestine. To characterize the ontogeny of the digestive function of these PLA 2s, the present study investigated the localization and expression of DE-1 and DE-2 PLA 2 genes in red sea bream larvae/juveniles and immature adults, by in situ hybridization. In the adults, DE-1 PLA 2 mRNA was expressed in pancreatic acinar cells. By contrast, DE-2 PLA 2 mRNA was detected not only in digestive tissues, such as pancreatic acinar cells, gastric glands of the stomach, epithelial cells of the pyloric caeca, and intestinal epithelial cells, but also in non-digestive ones, including cardiac and lateral muscle fibers and the cytoplasm of the oocytes. In the larvae, both DE-1 and DE-2 PLA 2 mRNAs first appeared in pancreatic tissues at 3 days post-hatching (dph) and in intestinal tissue at 1 dph, and expression levels for both gradually increased after this point. In the juvenile stage at 32 dph, DE-1 PLA 2 mRNA was highly expressed in pancreatic tissue, and DE-2 PLA 2 mRNA was detected in almost all digestive tissues, including pancreatic tissue, gastric glands, pyloric caeca, and intestine, including the myomere of the lateral muscles. In conclusion, both DE-1 and DE-2 PLA 2 mRNAs are already expressed in the digestive organs of red sea bream larvae before first feeding, and larvae will synthesize both DE-1 and DE-2 PLA 2 proteins.

Enhancement of gilthead seabream (Sparus aurata) larval growth by dietary vitamin E in relation to two different levels of essential fatty acids

The objective of this study was to determine the effect of dietary vitamin E on gilthead seabream (Sparus aurata) growth and survival, at two different highly unsaturated fatty acids (HUFAs) levels. Eighteen days old gilthead seabream larvae were fed four formulated experimental diets combining two different dietary levels of HUFAs (M: medium 2.5 + 1.5, DHA + EPA, H: high 5 + 2.5 DHA + EPA g per 100 g) with two different levels of vitamin E (M: medium 540 mg kg−1, H: high 2900 mg kg−1): MM, MH, HM, HH (HUFA/vitamin E). After 2-week feeding trial, the average survival rate was 52.6% and there were no significant differences found among treatments. Increase in vitamin E up to high level markedly improved larval growth, particularly when dietary HUFA levels were lower, suggesting a higher protection value when these fatty acids are more limiting. At medium dietary HUFA levels, increase in vitamin E from medium to high level enhanced larval growth performance in terms of total length. Moreover, increase in vit E enhanced HUFAs content in the larval polar lipids denoting the anti-oxidative effect of vitamin E.

Increased Mauthner cell activity and escaping behaviour in seabream fed long-chain PUFA

There is limited information on the specific effects of long-chain PUFA (LCPUFA) on neuron development and functioning. Deficiency of those essential fatty acids impairs escape and avoidance behaviour in fish, where Mauthner cells (M-cells) play a particularly important role in initiating this response. Gilthead seabream larvae fed two different LCPUFA profiles were challenged with a sonorous stimulus. Feeding n-3 LCPUFA increased the content of these fatty acids in fish tissues and caused a higher number of larvae to react to the stimulus with a faster burst swimming speed response. This faster startle response in fish fed n-3 LCPUFA was also associated with an increased immune-positive neural response, particularly in M-cells, denoting a higher production of acetylcholine. The present study shows the first evidence of the effect of n-3 LCPUFA on the functioning of particular neurons in fish, the M-cells and the behaviour response that they modulate to escape from a sound stimulus.

Effects of turbidity on survival of larval ayu and red sea bream exposed to predation by jack mackerel and moon jellyfish

We conducted laboratory experiments to examine the effects of turbidity on the survival of red sea bream Pagrus major and ayu Plecoglossus altivelis altivelis larvae when exposed to either visual (jack mackerel juveniles) or tactile (moon jellyfish) predators. The experiments were conducted in 30-l tanks with three different levels of turbidity obtained by dissolving 0, 50, or 300 ppm kaolin. Predators were introduced to the experimental tanks followed by larvae of either red sea bream (mean ± standard deviation 6.1 ± 0.3 to 11.4 ± 2.1 mm standard length) or ayu (6.6 ± 0.3 and 24.4 ± 1.8 mm). When exposed to jack mackerel, the mean survival rate of larvae was significantly higher in 300 ppm treatments compared with the other turbidity levels. When exposed to moon jellyfish, however, there was a less marked difference in the survival rates among different turbidity treatments. Survival rates of ayu larvae exposed to moon jellyfish were generally lower than those of red sea bream. Our study indicates that anthropogenic increases of turbidity may increase the relative impact of jellyfish predation on fish larvae.

Effect of rotifer enrichment with herbal extracts on growth and resistance of red sea bream, Pagrus major (Temminck &amp; Schlegel) larvae against Vibrio anguillarum

The effects of the dietary medicinal herbs Massa medicata, Crataegi fructus (Cf), Artemisia capillaries, Cnidium officinale and their mixture (HM), on growth and resistance against Vibrio anguillarum were examined using larval red sea bream, Pagrus major. The methanol extracts of Cf and HM inhibited the proliferation of seven infectious bacterial strains including the genera Aeromonas, Edwasiella, Photobavterium, Pseudomonas and Vibrio. Rotifers enriched with emulsified bonito oil containing extracts of Cf and HM lowered the bacterial counts in their body on TCBS medium for the genus Vibrio in comparison with rotifers enriched by emulsified bonito oil alone. Although statistically not significant, larvae fed rotifer fortified with Cf from 3 to 20 days after hatching showed the best growth and final body weight followed by those given rotifer with HM and control enrichment. However, final body length of larvae fed rotifer with Cf was significantly larger than larvae fed on rotifers enriched with other herb extracts. After a challenge test with V. anguillarum, survival of larvae fed rotifer with Cf and HM was significantly higher than for the control treatment. These results revealed that Cf and HM in rotifer is useful to promote growth and resistance against V. anguillarum in red sea bream larvae, providing a new technology for mass production of disease-resistant fry and fingerlings.

Importance of the relative levels of dietary arachidonic acid and eicosapentaenoic acid for culture performance of gilthead seabream (Sparus aurata) larvae

The effect of different arachidonic acid (ARA) dietary contents at several dietary eicosapentaenoic acid (EPA) levels on the growth, survival and biochemical composition of gilthead seabream larvae was studied to better define the importance of this fatty acid as a function of EPA. Larvae of 18 days were fed one of the five isonitrogenous and isolipidic microdiets with three different EPA (0.3%, 2% and 4%) and ARA amounts (0.1%, 0.6% and 1.2%). Although a dietary increase in either ARA or EPA alone did not improve survival significantly, the increase in both fatty acids significantly enhanced growth and survival, suggesting an optimum dietary value of EPA:ARA close to 4:1.2. Dietary ARA was more efficiently incorporated into larval tissues than EPA. Increased dietary EPA or ARA contents reduced the incorporation of ARA or EPA into larval lipids, indicating their competition as substrates for different enzymes. The possible negative effect of further elevation of dietary ARA and its competition with EPA for phospholipids synthesis deserves further studies in marine fish larvae.

Toxicity of parathion on embryo and yolk‐sac larvae of gilthead seabream (Sparus aurata l.): Effects on survival, cholinesterase, and carboxylesterase activity

This study was conducted to examine the acute toxicity of the organophosphorus pesticide (OP) parathion on embryos and yolk-sac larvae of gilthead seabream (Sparus aurata), and to investigate the effects of this compound on cholinesterase and carboxylesterase activity of seabream larvae in the phase of endogenous feeding. The 72-h LC50 for yolk-sac larvae (0.523 mg L⁻¹) was about two-fold lower than the 48-h LC50 for embryos (1.005 mg L⁻¹). Parathion significantly inhibited the activity of ChE and CaE activity in yolk sac larvae but there were not significant differences in the sensitivity of both esterases to parathion as inferred by their 72-h IC50 values. Larvae exposed to parathion for 72 h showed a 70% inhibition of the whole body acetylcholinesterase at approximately the LC50.

Effects of feeding of carotenoids supplement rotifer on splenocyte proliferation reaction of red sea bream larvae (Pagrus major) and tiger puffer (Takifugu rubripes)

Effects of feeding of carotenoids supplement rotifer on splenocyte proliferation reaction of red sea bream larvae (Pagrus major) and tiger puffer (Takifugu rubripes)

Can dietary aromatic amino acid supplementation be beneficial during fish metamorphosis?

Aromatic amino acids (AA, phenylalanine and tyrosine) are the precursors of thyroid hormones, which regulate metamorphosis in all vertebrates. In fish, this is a critical developmental stage where physiological requirements for aromatic AA may increase. Therefore, it is possible that dietary aromatic AA supplementation may be beneficial to accomplish a successful transition from larvae to the juvenile stage. This work aimed to assess the effect of dietary aromatic AA supplementation on tyrosine metabolism in species with an accentuated (Senegalese sole, Solea senegalensis) and a less marked (gilthead seabream, Sparus aurata) metamorphosis. For this purpose, either species were fed Artemia and subsequently received or not an aromatic AA supplement through tube-feeding, together with a L-[U- 14C] tyrosine marker, throughout metamorphosis. Tyrosine was elected as a tracer since the metabolic fate of this aromatic AA is directly linked to the production of thyroid hormones and metamorphosis. Results showed that dietary phenylalanine supplementation did not increase tyrosine retention in Senegalese sole larvae during metamorphosis, suggesting that this species may not be able to biosynthesise tyrosine from phenylalanine at a sufficient rate to supply its physiological requirements until after metamorphosis. Furthermore, dietary tyrosine supplementation effectively increased tyrosine availability in Senegalese sole body fluids at metamorphosis, most likely for coping with metamorphosis-related processes, such as production of thyroid hormones. Therefore, dietary tyrosine supplementation may be beneficial for Senegalese sole during metamorphosis. On the other hand, results indicated that gilthead seabream larvae do not seem to require an additional supply of aromatic AA during metamorphosis, probably because the physiological requirements for tyrosine do not increase during this developmental stage. The different results observed for Senegalese sole and gilthead seabream are probably related to the complexity of metamorphosis that each species undergoes and to the needs for production of thyroid hormones, which seems to affect aromatic AA requirements during this critical stage of development. These findings may be important for physiologists, fish nutritionists and for the flatfish aquaculture industry.

Influence of Microalgae Supernatant, and Bacteria Isolated from Microalgae Cultures, on Microbiology, and Digestive Capacity of Larval Gilthead Seabream, Sparus aurata, and Senegalese Sole, Solea senegalensis

This study aimed at investigating addition of microalgae in the rearing of marine fish larvae (green water technique). Addition of microalgae supernatant, or bacteria isolated from microalgae cultures, to the rearing tanks of larval Senegalese sole, Solea senegalensis, and gilthead seabream, Sparus aurata, had no significant (P < 0.05) influence on survival or growth of the larvae. Addition of four bacterial strains isolated from microalgae decreased however the numbers of presumptive Vibrio in gilthead seabream larvae and seawater were compared with the control treatment 7 d after hatching (P < 0.05). No such effects were shown on the numbers of presumptive Vibrio in the rearing of sole larvae. Addition of bacteria improved the digestive capacity of gilthead seabream larvae, as the total activity (U/larva) of trypsin, amylase, and alkaline phosphatase in the treatment with added bacteria were significantly higher (P < 0.05) than in larvae from the control treatment 10 d after hatching. No such effects were shown in the case of sole larvae. The present results indicated that bacteria associated with microalgae may play an important role for the inhibition of proliferation of Vibrio and improvement of digestive capacity during the first days of feeding of gilthead seabream larvae, but does not appear to be beneficial for larvae of Senegalese sole.

Influence of temperature on muscle fibre hyperplasia and hypertrophy in larvae of blackspot seabream, Pagellus bogaraveo

The effects of temperature on Pagellus bogaraveo muscle cellularity were investigated, by morphometry, throughout the endogenous feeding stage, testing two rearing temperatures: 14 and 18 °C. The following parameters were estimated in transversal body sections at post-opercular and post-anal body levels: the total cross-sectional muscle area, the total number of fibres and the mean cross-sectional fibre area. At hatching, no significant influence of the temperature was observed on the morphometric parameters measured in the white muscle. At mouth opening, an increase in the number of post-opercular white fibres was promoted by the highest temperature. During embryonic development, the red muscle fibre number in the post-anal part of the larvae increased with higher temperature, but it appears that the difference was no longer present at mouth opening. An increase in the fibre area and in the total cross-sectional area of red muscle at the post-anal level was promoted by a 4 °C increase in the temperature during the vitelline phase. In conclusion, the axial musculature of blackspot seabream embryos/larvae reacted differently to temperature influence according to the body location, strongly supporting the need to look at and account for different body locations when evaluating muscle cellularity in fish, namely in growth/aquaculture-related studies.