Effect of the supplementation of live preys enriched in cod liver oil on the survival rate,growth and fatty acid profile of meagre (Argyrosomus regius) larvae

First‐feeding diets employed in the rearing of meagre (Argyrosomus regius) larvae are based on live preys that are commonly enriched to compensate for their deficiency of essential fatty acids. A feeding trial was conducted on meagre larvae (Argyrosomus regius) fed rotifer (Brachionus plicatilis) and Artemia salina enriched in lipids from an emulsion of cod liver oil (CLO) and a commercial product (CP). The effect of both enrichment products was evaluated on the survival rate, size and lipid composition of meagre larvae. The results showed that larvae fed CLO presented significant higher values of survival rate (35.0 ± 3.2%) and larval size (12.06 ± 1.17 mm) at the end of the experiment, compared to the CP diet (26.0 ± 2.5%, 11.41 ± 0.91 mm, respectively). Both zootechnical parameters were related to the content of polyunsaturated fatty acids in the larvae. Indeed, the larvae fed CLO presented a higher ratio DHA/EPA than those enriched in commercial product (0.82 ± 0.18 and 0.38 ± 0.12 at 26 days after hatching, respectively). Both larval groups presented similar body content of arachidonic acid (1.4 wt.% on average at 26 days after hatching), regardless the enrichment source. From all above, we can conclude that the enrichment of live preys with an emulsion of cod liver oil is an economically viable alternative to commercial products. Indeed, cod liver oil emulsions are able to fully meet the requirements for fatty acids of meagre larvae. Furthermore, cod liver oil is easily available from fish processing facilities.     

The importance of dietary HUFA for meagre larvae (Argyrosomus regius; Asso, 1801) and its relation with antioxidant vitamins E and C

Despite the interest of meagre (Argyrosomus regius) as a fast‐growing candidate for Mediterranean aquaculture diversification, there is a lack of information on nutrition along larval development. Importance of highly unsaturated fatty acids (HUFA) and the antioxidant vitamins E and vitamin C has not been investigated yet in this species. Six diets with two levels of HUFA (0.4% and 3% dw), two of vitamin E (1500 and 3000 mg kg^?1) and two of vitamin C (1800 and 3600 mg kg^?1) were fed to 15 dah meagre larvae. Larval growth in total length and dry body weight was significantly lowest in larvae fed diet 0.4/150/180 and showed few lipid droplets in enterocytes and hepatocytes and lower HUFA contents than the initial larvae. Increase in dietary HUFA up to 3%, significantly improved larval growth and lipid absorption and deposition. Besides, among fish fed 3% HUFA, increase in vitamin E and vitamin C significantly improved body weight, as well as total lipid, 22:6n‐3 and n‐3 fatty acids contents in the larvae. Thus, the results showed that 0.4% dietary HUFA is not enough to cover the essential fatty acid requirements of larval meagre and a high HUFA requirement in weaning diets is foreseen for this species. Besides, the results also pointed out the importance of dietary vitamin E and C to protect these essential fatty acids from oxidation, increase their contents in the larvae and promote growth, suggesting high vitamin E and C requirements in meagre larvae (higher than 1500 and 1800 mg kg^?1 for vitamin E and vitamin C respectively).     

Effect of increased dietary protein level in meagre (Argyrosomus regius) juvenile growth and muscle cellularity

In this study, two different dietary protein levels were tested (500 and 600 g/kg) in meagre juveniles of approximately 2 g, to determine whether a higher body protein diet would favour muscle growth. Results showed that meagre survival and growth were not affected by different levels of dietary protein. However, a higher content of protein was observed in the body composition of meagre fed the P60 diet (656 g/kg versus 624 g/kg). When fish were 82 days after hatched (DAH), protein retention efficiency was significantly higher in fish that were fed the P50 diet (37.1% versus 32.5%). Muscle cellularity changed considerably from the beginning to the end of the trial. The contribution of fibre hyperplasia to muscle growth was reduced although still accounted for 30% in 96 DAH meagre. Several differences were found in the frequency of fibres with areas between 1,000 μm² and 2,200 μm² between younger and older meagre, but no effect was found associated with dietary protein. This study suggests that neither growth nor muscle cellularity of fast‐growing juvenile meagre is positively affected by an increased dietary protein levels.     

Reduction of skeletal anomalies in meagre (Argyrosomus regius,Asso, 1801) through early introduction of inert diet

The consolidation of meagre (Argyrosomus regius) in aquaculture requires an understanding and optimization of larval rearing and nutritional conditions. The aim of this study was to analyse the effects of an early introduction of inert diets during larval rearing, on growth performance, digestive enzymes activity and development of skeletal anomalies. This study evaluated the effects of three different timings for the introduction of inert diet during larval rearing: a control group (CTRL) where inert diet was initiated at 14 days after hatching (DAH) and two treatment groups that had an earlier introduction of inert diet at 8 DAH (T1) and 11 DAH (T2). Meagre larvae exhibited similar pancreatic and intestinal enzymatic activities among the different dietary treatments. No differences in the overall prevalence of anomalies were observed between treatments at 25 or 50 DAH, however, a significant reduction was observed in all groups with the transition from larval to juvenile stage. The precocious introduction of inert diet shifted the distribution of vertebral anomalies to a more anterior vertebral column region. Altogether, this study shows that earlier introduction of inert diets in meagre hatcheries can be beneficial for meagre production in aquaculture.     

A balanced amino acid diet improves Diplodus sargus larval quality and reduces nitrogen excretion

Fish larvae present high amino acid requirements due to their high growth rate. Maximizing this growth rate depends on providing a balanced amino acid diet which can fulfil larval amino acid nutritional needs. In this study, two experimental microencapsulated casein diets were tested: one presenting a balanced amino acid profile and another presenting an unbalanced amino acid profile. A control diet, live feed based, was also tested. Trials were performed with larvae from 1 to 25 days after hatching (DAH). Microencapsulated diets were introduced at 8 DAH in co-feeding with live feed and at 15 DAH larvae were fed the microencapsulated diets alone. Results showed a higher survival for the control group (8.6 ± 1.3% versus 4.2 ± 0.6% and 3.2 ± 1.8%) although dry weight and growth were similar in all treatments. The proportion of deformed larvae as well as the ammonia excretion was lower in the group fed a balanced diet than in the unbalanced or control groups (38.3% deformed larvae in control, 30% in larvae fed unbalanced diet and 20% on balanced diet group). Furthermore, larvae fed the microencapsulated diets presented higher docosahexaenoic acid and arachidonic acid levels. This study demonstrates that dietary amino acid profile may play an important role in larval quality. It also shows that balanced microencapsulated diets may improve some of the performance criteria, such as skeletal deformities, compared to live feeds.     

Co-feeding of live feed and inert diet from first-feeding affects Artemia lipid digestibility and retention in Senegalese sole (Solea senegalensis) larvae

The present study intended to evaluate the effects of early introduction of inert diet in lipid digestibility and metabolism of sole, while larval feed intake, growth and survival were also monitored. Solea senegalensis larvae were reared on a standard live feed regime (ST) and co-feeding regime with inert diet (Art R). Trials using sole larvae fed with Artemia enriched with two different lipid emulsions, containing glycerol tri [1-¹⁴C] oleate (TAG) and L-3-phosphatidylcholine-1,2-di-[1-¹⁴C] oleoyl (PL), were performed at 9 and 17 days after hatching (DAH) to study lipid utilization. Co-feeding did not affect sole survival rates (ST 59.1 ± 15.9%; Art R 69.56 ± 9.3%), but was reflected in significantly smaller final weight at 16 DAH (ST 0.71 ± 0.20; Art R 0.48 ± 0.14 mg). Higher feed intake was observed in sole larvae fed on Artemia enriched with labeled PL at 9 DAH but not at 17 DAH. At 17 DAH, the smaller larvae (Art R treatment) ingested proportionally more Artemia in weight percentage, independently of enrichment. At 9 DAH lipid digestibility was equal among treatments and higher than 90%, while at 17 DAH it was higher in ST treatment (around 73%) compared to the Art R group (around 66%). Lipid retention efficiency at 9 DAH was higher in the Art R treatment, reaching values of 50%, while these values almost duplicated at 17 DAH, ranging up to 80% in both treatments without significant differences. These results show that co-feeding of live feed and inert diet from first-feeding in Senegalese sole has a toll in terms of growth and lipid digestibility but does not seem to compromise lipid metabolic utilization.     

Is it possible to successfully rear meagre (Argyrosomus regius Asso 1801) larvae without using rotifers?

In hatcheries, meagre Argyrosomus regius larvae still depend on an adequate supply of rotifers and Artemia, as no artificial diet can totally fulfil their nutritional requirements. However, production of live feed is highly expensive and demands intensive labour and specific facilities. This study investigated the effect of a dietary regime without the use of rotifers, to simplify the meagre larval rearing protocol. Two feeding treatments (T₁ & T₂) are compared to investigate their effects on survival and growth of meagre larvae. In T₁, larvae were fed rotifers from 2 to 5 days post hatch (dph), and Artemia from 4 to 15 dph. In T_2, larvae were kept under dark conditions and fed Artemia from 6 to 15 dph. Standard larval length (SL) was significantly higher in T₁ (p < .01) until 8 dph in comparison with larvae reared initially without rotifers. No significant difference in SL was found among treatments (p = .187) at 15 dph. Significant difference was found among treatments in survival rate at 15 dph (p < .003). The survival rate observed at 15 dph in T₂ (30 ± 4.2%) represents an important finding, although the highest survival rate was observed in T₁ (45.0 ± 3.4%). This study showed that it is possible to conduct larval rearing of meagre without using rotifers. Nevertheless, further research efforts are still needed to improve these results in comparison with the common larval rearing protocol.     

Effect of different enrichment products rich in docosahexaenoic acid on growth and survival of meagre,Argyrosomus regius (Asso, 1801)

Live prey used in aquaculture to feed marine larval fish – rotifer and Artemia nauplii – lack the necessary levels of n‐3 polyunsaturated fatty acids (n‐3 PUFA) which are considered essential for the development of fish larvae. Due to the high voracity, visual feeding in conditions of relatively high luminosity, and cannibalism observed in meagre larvae, a study of its nutritional requirements is needed. In this study, the effect of different enrichment products with different docosahexaenoic acid (DHA) concentrations used to enrich rotifers and Artemia metanauplii have been tested on growth, survival, and lipid composition of the larvae of meagre. The larvae fed live prey enriched with Algamac 3050 (AG) showed a significantly higher growth than the rest of the groups at the end of the larval rearing, while the larvae fed preys enriched with Multigain (MG) had a higher survival rate. DHA levels in larvae fed prey enriched with MG were significantly higher than in those fed AG‐enriched prey. High levels of DHA in Artemia metanauplii must be used to achieve optimal growth and survival of meagre larvae.     

Influence of dietary lipid on growth performance and some lipogenesis‐related gene expression of tongue sole (Cynoglossus semilaevis) larvae

A 30‐day feeding trial was conducted to investigate the effects of dietary lipid levels on growth performance, activities of digestive enzymes, fatty acid composition and some lipogenesis‐related gene expression of half‐smooth tongue sole (Cynoglossus semilaevis) larvae. Five isoproteic diets were formulated with graded lipid levels (6.68%, 9.84%, 13.47%, 17.89% and 21.88% dry weight) using fish oil as the main lipid source. Each diet was randomly allocated to triplicate groups of 150 larval tongue sole (35 DAH, 54 ± 1 mg). Fish were fed five times daily to apparent satiation during the feeding experiment. Results showed that, the survival rate (SR) of larvae increased significantly firstly, and thereafter decreased significantly. The specific growth rates (SGR) of larvae fed the diet with 13.47% lipid were significantly higher than other treatments. Larvae fed 9.84% or 13.47% dietary lipid showed higher trypsin, lipase, leucine aminopeptidase and alkaline phosphatase (AP) activities than other treatments, whereas amylase activity nearly showed reverse trend with them. The fatty acid composition of the tongue sole larvae was well correlated with dietary fatty acid profile. Expression of acetyl‐CoA carboxylase alpha (ACC1) was found to be slightly negatively correlated with dietary lipid level, and high dietary lipid level depressed the expressions of acetyl‐CoA carboxylase beta (ACC2) and fatty acid synthase (FAS) mRNA expression significantly, implying that larvae may cope with high dietary lipid mainly through down‐regulating lipogenesis‐related gene expression of FAS and ACC2. Besides, on the basis of SGR, the optimal dietary lipid level for larval tongue sole was estimated to be 13.56% using second‐order polynomial curve.     

Amino acid profiles of Diplodus sargus (L., 1758) larvae: Implications for feed formulation

The indispensable AA profile of fish carcass has been commonly used as a good indicator of fish amino acids requirements. Amino acid composition of the whole body tissue of Diplodus sargus was determined for the larval ages of 0, 2, 5, 8, 12, 17, 25, 35 and 45 days after hatching (DAH). No significant differences were found during this species ontogeny, except for phenylalanine. A comparative analysis of amino acid profiles from larvae and respective diet was performed. Low correlation was found to rotifers (R² approximately 0.5), while higher correlations were found for Artemia nauplli, metanauplii (R² approximately 0.8) as well as for the dry feed. These results suggest that D. sargus are subjected to higher nutritional imbalances during the first 10 days of feeding when larvae are fed on rotifers alone. Arginine, threonine, lysine, cysteine and histidine appeared to be limiting amino acids at 2, 12, 25 and 45 DAH, respectively. Similar results were reported in literature for Sparus aurata and Solea senegalensis, although D. sargus diets seem to have more amino acids in deficiency as well as more severe differences between larval and diet amino acid profiles. To solve these apparent nutritional imbalances, amino acid supplementation should be considered. The use of inert diets in early larvae ages seems to be most adequate as live feed supplementation appears to be more difficult.     

Dietary indispensable amino acids profile affects protein utilization and growth of Senegalese sole larvae

In diet formulation for fish, it is critical to assure that all the indispensable amino acids (IAA) are available in the right quantities and ratios. This will allow minimizing dietary AA imbalances that will result in unavoidable AA losses for energy dissipation rather than for protein synthesis and growth. The supplementation with crystalline amino acids (CAA) is a possible solution to correct the dietary amino acid (AA) profile that has shown positive results for larvae of some fish species. This study tested the effect of supplementing a practical microdiet with encapsulated CAA as to balance the dietary IAA profile and to improve the capacity of Senegalese sole larvae to utilize AA and maximize growth potential. Larvae were reared at 19 °C under a co-feeding regime from mouth opening. Two microdiets were formulated and processed as to have as much as possible the same ingredients and proximate composition. The control diet (CTRL) formulation was based on commonly used protein sources. A balanced diet (BAL) was formulated as to meet the ideal IAA profile defined for Senegalese sole: the dietary AA profile was corrected by replacing 4 % of encapsulated protein hydrolysate by CAA. The in vivo method of controlled tube-feeding was used to assess the effect on the larvae capacity to utilize protein, during key developmental stages. Growth was monitored until 51 DAH. The supplementation of microdiets with CAA in order to balance the dietary AA had a positive short-term effect on the Senegalese sole larvae capacity to retain protein. However, that did not translate into increased growth. On the contrary, larvae fed a more imbalanced (CTRL group) diet attained a better performance. Further studies are needed to ascertain whether this was due to an effect on the voluntary feed intake as a compensatory response to the dietary IAA imbalance in the CTRL diet or due to the higher content of tryptophan in the BAL diet.     

Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance,non‐specific immune responses and disease resistance in rainbow trout,Oncorhynchus mykiss

We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non‐specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk^® (MS), with Song‐Gang^® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8‐week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non‐specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non‐specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song‐gang^® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.     

Early life history of yellow puffer,Chonerhinos naritus (Richardson, 1848) from Sarawak,Northwestern Borneo

The growth and morphological development including fins, spine distribution and pigmentation of larval and juvenile of hatchery‐reared yellow puffer, Chonerhinos naritus were described to provide essential information on the early life history of this species. The total length (TL) of newly hatched larvae was 3.42 ± 0.23 (mean ± SD) mm, reaching 5.66 ± 0.38 mm on 5 days after hatched (DAH), 7.80 ± 0.28 mm on 11 DAH, 9.88 ± 0.40 mm on 27 DAH and 10.92 ± 0.58 mm on 30 DAH. The yolk was completely absorbed in preflexion larvae at 4 DAH. The mouth opening started at 3 DAH of yolk sac larvae, while the teeth appeared starting from preflexion larvae at 7 DAH. Overall aggregate fin ray numbers including caudal fin attained full complement in postflexion larvae at 27 DAH. Several melanophores with appearance of small stellate were first appeared dorsally on the head of flexion larvae at 13 DAH, expanded at the dorsal region of the head, above the eye in juveniles at 30 DAH. The spines first appeared in preflexion larvae of C. naritus at 7 DAH, covering the ventral skin region below pectoral fin base and expanded to the ventral part of the body and nearly covered the whole abdomen region before the anus and below the eyes in juveniles. C. naritus remain as larvae for approximately 29 days, during which they metamorphose to the juvenile stage prior to sexual maturation. Observations in larvae development of C. naritus revealed similar characteristics with other Tetraodontidae species.     

Lack of essential fatty acids in live feed during larval and post-larval rearing: effect on the performance of juvenile <Emphasis Type="Italic">Solea senegalensis</Emphasis>

Despite the large progress obtained in recent years, Senegalese sole (Solea senegalensis) production of high quality juveniles is still a bottleneck. This paper examines the effect of larval and post-larval lipid nutrition on juvenile performance and quality. Four dietary treatments were tested: A—enriched Artemia spp. (EA); B—non-enriched Artemia spp. (NEA); C—EA during the pelagic larval period and NEA after larval settlement; D—50% EA and 50% NEA. Juvenile fatty acid profile at 60 days after hatching (DAH) clearly reflected the larval and post-larval diet composition. Feeding sole larvae on NEA (poor in lipids and essential fatty acids-EFA) had a negative effect, reducing growth (total length and dry weight) after 30 DAH and decreasing digestive enzyme activity at the end of the rearing period (60 DAH). However, relatively good performance compared to the EFA-richest treatment (A) was obtained when larvae were fed 50% EA and 50% NEA (D) or even EA only during the pelagic larval period followed by NEA after larval settlement (C). Malpigmentation was not affected by the dietary regimes and its incidence was very low. However, skeletal deformities were prevalent, particularly in the caudal complex, independently of diet. The results confirm that Senegalese sole appear to have lower larval EFA requirements than most cultured marine species and potentially even lower requirements during the post-larval stage. The importance of studying the impact of early nutrition on later juvenile stages was clearly highlighted in this study.     

Effect of dietary microminerals in early weaning diets on growth,survival, mineral contents and gene expression in gilthead sea bream (Sparus aurata,L) larvae

In previous studies, combined inclusion of Zn, Mn and Se in early weaning diets improved larval growth, but suggested a potential toxicity by one of these elements. The present study aimed to determine the effect of the single inclusion of Zn, Mn, Se or Cu, their combination (Control+) or their absence (Control?) on larval diets. At the end of the trial, survival was significantly (p < .05) lowest in fish fed C+ diet (17.16 ± 7% mean ± SD), followed by that of larvae fed Mn diet (21.91 ± 7%). The highest survival was obtained by Cu diet (35.27 ± 15%), followed by C? diet (34.58 ± 9%). Cu and Se supplementation significantly improved total length and body weight, in comparison with the C? fish. On the contrary, fish fed Mn and C+ showed the lowest growth. Supplementation with Zn or Cu significantly increased CuZnsod, whereas gpx was significantly upregulated in fish fed Se and C+ diets. ARA/EPA level was significantly highest and DHA/EPA lowest in larvae fed the Cu diet in fish fed C+ diet. The results pointed out the importance of supplementation with Cu, as well as Se and Zn, on early weaning diets for gilthead sea bream, and the potential toxic effect of Mn.     

Amino acid profiles and amino acid utilization in larval African catfish (Clarias gariepinus): effects of ontogeny and temperature

The present study investigated the qualitative amino acid (AA) requirements of larval African catfish Clarias gariepinus. Yolk-sac larval AA profiles were measured at different temperatures and also in animals reared at 28 °C fed Artemia nauplii or an experimental dry diet. The AA profile of C. gariepinus larvae changed during ontogeny, especially before the start of exogenous feeding. The AA profiles of the food items (yolk, Artemia and the dry diet) differed considerably from that of the larvae. No selective absorption of yolk AA was detected. Higher temperatures led to increased absorption and depletion rates of AA, and also to a higher retention efficiency of yolk nutrients. However, changes in temperature did not induce preferential absorption or depletion of individual AA, and caused only small variations in the AA profile. Depletion rates of individual AAs varied, possibly due to differences between larval and yolk AA profiles, and also to changes in the larval AA profile during ontogeny. There was little regulation of catabolism of individual AA in yolk-sac and starved larvae, and no sparing of essential AA.     

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.     

Effects of different natural or prepared diets on growth and survival of juvenile spider crabs, <Emphasis Type="Italic">Maja brachydactyla</Emphasis> (Balss, 1922)

The effects of different diets (natural or pellets) on growth, survival, and moulting interval of juvenile spider crabs, weighing between 0.011–1.56 g and up to 17.6 mm in carapace length, were tested over a period of 90 days. During experiment I, five diets were tested: (1) frozen shrimp—Paleomonetes sp., (2) fresh mussels—Mytilus sp., (3) white fish fillets—Merlucius merlucius, (4) blue fish fillets—Sardina pilchardus, and (5) commercial crustacean pellets. Spider crabs fed fresh mussels grew larger (0.98 ± 0.69 g) and had higher growth rates (4.0 ± 0.7 %BWd⁻¹) compared to the other four diets. The crabs fed shrimp pellet and frozen shrimp grew to intermediate sizes and were smaller than the ones fed fresh mussels, but they were larger than spider crabs fed either blue or white fish fillets (0.46 ± 0.63 and 0.26 ± 0.13 g, respectively) compared to the ones fed white fish fillets (0.12 ± 0.04) and blue fish fillets (0.04 ± 0.02 g). The spider crabs fed blue fish fillets only lasted until day 60 of the experiment, after this day none of the 20 fed this diet were left. During experiment II, two diets were tested: (1) white and blue fish fillets and (2) commercial fish pellet. There were no differences in growth both in weight or carapace length (2.9 ± 1.8 and 2.1 ± 1.5 g in weight, and 18.9 ± 5.0 and 17.7 ± 3.3 mm, respectively) at the end of the experiment. Similarly, there were no differences in growth rates in weight between the two diets (1.2 ± 0.4 and 0.9 ± 0.3 %BWd⁻¹, respectively) or in carapace length (0.4 ± 0.1 and 0.4 ± 0.2 %BWd⁻¹, respectively). Fresh mussel appears to be a very good diet to culture the early stages of this species, while shrimp pellets also deliver acceptable results. On the contrary, frozen shrimp, fish fillets either from blue or white species (much higher lipid content in the blue species), and fish pellets were found to be bad diets for the culture of the early stages of M. brachydactyla.     

Evaluation of dietary histidine supplementation on meagre,Argyrosomus regius,juvenile growth,haematological profile,stress and muscle cellularity

Histidine plays an important role in haemoglobin synthesis, antioxidant defence system and stress resistance, and it is thought to be a limiting amino acid in most meagre diets. In this study, two different diets, a control and a diet supplemented with 3% histidine, were tested in 60‐day‐old meagre (initial weight—6.2 g) for 82 days. Survival varied between 92% and 94%, and neither SGR nor whole fish composition seemed to be affected by the diet. When fish were submitted to a stress test (outside water for 30 s), it was observed that the levels of glucose and lactate significantly increased in both treatments. The concentration of cortisol increased after the stress test only in the His 30 g/kg group. Muscle cellularity was affected by the diets, where the control group showed a higher mean fibre area and lower fibre density. These results, associated with a lower frequency of smaller fibres, suggest a decrease in fibre recruitment and a higher fibre hypertrophy. In conclusion, the supplementation of diets with 3% led to a more pronounced response to the stress test in terms of cortisol levels and increased muscle fibre recruitment, decreasing muscle fibre hypertrophy contribution to muscle growth.