J.L. Zambonino Infante

Early weaning of sea bass (Dicentrarchus labrax) larvae with a compound diet: Effect on digestive enzymes

Abstract Sea bass (Dicentrarchus labrax) larvae were weaned with a microparticulated diet at various times after hatching: 10, 15, 20 and 25 days; a control group was fed live prey (Artemia salina). The earlier the weaning, the lower the larval growth obtained. The amylase activity in the pancreatic segment increased swiftly after the weaning in all groups. This increase was the result of an extensive synthesis induced by the starch content (12%) of the compound diet. The enhancement of specific activities of intestinal peptidases, leucine aminopeptidase and γ-glutamyl transpeptidase after weaning was the result of compensatory adaptation, as was described in the case of malnutrition. The depressed activities of alkaline phosphatase, in the brush border membrane fraction, indicated malnutrition in weaned groups. Weaning before day 20 stops or delays larval development, particularly maturation of some digestive processes in larvae, such as the onset of pancreas secretory functions.

Protein hydrolysate vs. fish meal in compound diets for 10-day old sea bass Dicentrarchus labrax larvae

Abstract Four groups of Dicentrarchus labrax larvae were fed from day 10 post-hatching to day 41 with four isoenergetic and isonitrogenous (60%) compound diets differing only by the incorporation level of a commercial fish protein hydrolysate, CPSP G. In diet H0, the protein fraction was fish meal. In diets H19, H38 and H58, 25, 50 and 75% of the fish meal was replaced by CPSP, respectively. The four compound diets sustained larval growth throughout the experiment. The highest survival was obtained in the group fed H19 (47±5.0%). Final weights of larvae fed H0 and H19 diets (5.5±2.61 and 5.7±2.77 mg, respectively) were significantly higher than those of larvae fed diets H38 and H58 (3.3±1.03 and 2.6±0.70 mg, respectively). At day 41, the highest trypsin secretion levels were obtained in groups fed diets H0 and H19, suggesting a proper maturation of pancreatic digestive function. The incorporation of 19 and 38% hydrolysate in diets induced a high level of two membranous enzymes of intestine, alkaline phosphatase (AP) and aminopeptidase N (lap) as early as day 20. The cytosolic enzyme leucine–alanine peptidase (leu–ala) was also assayed. The ratios of AP/leu–ala and lap/leu–ala revealed that the development of the intestine was more advanced in the H19 fed group than in the others. The proper onset of intestinal digestive function was associated with good larvae survival. The experiment showed that the incorporation of a moderate dietary level of fish protein hydrolysate facilitates the onset of the adult mode of digestion in developing fish.

Development and response to a diet change of some digestive enzymes in sea bass (Dicentrarchus labrax) larvae.

Variations in some enzyme activities during larval development of sea bass fed live prey were investigated from hatching to day 40. Fluctuations in the enzyme specific activities (except for trypsin) occurred in three phases: initially a sharp increase until day 12, followed by a plateau and subsequently a decrease around day 23. Then activities remained constant until day 40. Trypsin activity kept rising until day 23, then fell. Enzymatic adaptation to a change in diet was studied by feeding larvae with microparticulate diet from day 25. Adaptation to dietary change was observed for amylase, alkaline phosphatase and leucine aminopeptidase, assayed in whole larvae. In larvae fed microparticulate dry diet, the activities of these three enzymes tended to be higher than in those fed natural prey. Although poor growth was observed in larvae fed microparticles, the brush border enzyme activities purified from whole body homogenate, were not impaired.

Dietary regulation of activities and mRNA levels of trypsin and amylase in sea bass (Dicentrarchus labrax) larvae

Specific activities and mRNA levels of trypsin and amylase were studied in sea bass larvae. From day 20 to day 40, Dicentrarchus labrax were fed two rations of one day old Artemia: satiation (LP) and one-eighth of the satiation ration (LP/8) or two isoenergetic compound diets that varied in protein (30 and 60%) and carbohydrate (37 and 7%) content (FP30 and FP60 respectively). Trypsin mRNA levels and specific activities were mainly influenced by the nature of dietary protein and the Artemia ration. By using fish meal as protein source, dietary protein concentration did not affect either mRNA level nor specific activity of trypsin. These results suggested that the trypsin synthesis was not affected at a transcriptional level by the protein ration, i.e., Artemia ration. Decrease in amylase mRNA observed from day 29 in the four dietary groups suggested that this decrease in amylase expression is genetically programmed during sea bass larvae development. Nevertheless, the composition and the quantity of the diet influenced the amylase specific activities revealing primarily translational regulation of amylase. This study shows for the first time that the molecular mechanisms which control the dietary adaptation of trypsin and amylase are independently regulated, age-dependent and influenced by the composition and the quantity of the diet.

Algal addition in sea bass (Dicentrarchus labrax) larvae rearing: effect on digestive enzymes

Abstract Two groups of Dicentrarchus labrax were reared from day 5 to day 20 post-hatching with live prey in running seawater with or without algae. The concentration of algae Isochryisis galbana was maintained between 20 000 to 40 000 cells ml −1 . On day 20, each group was divided into two subgroups, one still receiving live prey, the other fed a compound diet until day 32. On day 32, larvae fed live prey in the presence of algae exhibited an 18% higher survival than larvae reared without algae; in group fed compound diet, the algae supply induced a 26% survival enhancement. At day 16, it was observed a 40% weight improvement in the group reared in the presence of algae compared to the group reared without algae. At day 32, a slight but significant positive effect of algae on larvae weight was still noted in the group fed compound diet. From day 8 to day 16, the presence of algae in the rearing water resulted in an increase in trypsin activity whereas amylase and chymotrypsin were not affected. At day 26, alkaline phosphatase and maltase assayed in purified brush border membranes of intestine were significantly higher in larvae reared in seawater with algae than in those reared in clear water. This result suggests that the presence of algae facilitates the onset of hydrolytic functions of cell membranes. The significant improvement in survival of larvae reared in the presence of algae was related to the early development of brush border membranes. It is concluded that the algae acts by triggering digestive enzyme production, at both the pancreatic and intestinal level.

Maturation of the pancreatic and intestinal digestive functions in sea bass (Dicentrarchus labrax): effect of weaning with different protein sources.

The maturation of the digestive functions in sea bass (Dicentrarchus labrax) larvae was evaluated by the enzymatic profile of pancreas and intestine brush border membranes. Sea bass larvae were weaned at day 25 with three simplified diets different by their protein nature: 100% fish meal (FP), 100% casein mixture (CP) and 50% fish meal-50% casein mixture (CFP). The casein mixture contained 35% of hydrolysate. The control group was fed live preys. The specific activity of amylase decreased with age irrespectively of the diets whereas the specific activity of trypsin was enhanced. The casein mixture reduced pancreatic secretion in amylase and trypsin. The CFP group differed from the other groups fed on compound diets, exhibiting as soon as day 32 high activities of brush border enzymes, similar to controls. This sharp increase between day 25 and 32 appeared to be crucial for larval survival. The addition of a protein hydrolysate in a weaning diet seems to facilitate this maturation process.

Effect of the molecular form of dietary nitrogen supply in sea bass larvae: Response of pancreatic enzymes and intestinal peptidases.

Sea bass (Dicentrarchus labrax) larvae were weaned at day 25 with microparticulated diets in which 10% of the nitrogen supply had different molecular forms: amino acid mixture (SLAA), casein hydrolysate (SLH) or fish meal (SLP). The control group (LP) was fed live prey. No difference was observed in larval growth between the weaned groups, but the survival was significantly higher in the SLH group. Trypsin secretion was stimulated in the SLAA group, whereas the SLH diet reduced the secretion from the exocrine pancreas. The activity of the leucine-alanine peptidase, located in the cytosol of enterocytes, remained high in all weaned groups. However, the activity of the peptidases of the brush border membrane increased during the development phase in the control group. These results suggest that weaning with a classic compound diet delays enterocyte differentiation by maintaining the larval features of digestion. A compound diet containing protein hydrolysate can attenuate the delay of intestinal maturation.

Preliminary results on sea bass (Dicentrarchus labrax) larvae rearing with compound diet from first feeding. Comparison with carp (Cyprinus carpio) larvae

Abstract Three compound diets, based on fish protein hydrolysate and yeast (diet A), soybean protein concentrate and yeast (diet B) and fish meal (diet C), were tested with start-feeding sea bass and carp larvae, during 28 days at 19°C (4 replicates) and 20 days at 24°C (3 replicates), respectively. In sea bass larvae, diet A yielded better results (survival: 35±6%, mean weight: 3.4±0.8 mg) than diets B (survival: 14±2%, mean weight: 1.8±0.4 mg) and C (survival: 19±5%, mean weight 1.1±0.2 mg). In carp larvae, feeding diet A resulted in a high survival (86±7%) and the best growth (mean weight: 73±14 mg), diet B led to in a higher survival (98±1%) but to a lower growth (mean weight: 45±12 mg) and diet C gave the poorest survival (45±6%) and mean weight (11±1 mg). Thus, start-feeding sea bass larvae proved to be able to utilize compound diets, as previously shown in carp and other freshwater fish larvae. Although inferior to live food, diet A containing fish protein hydrolysate supported significant growth and survival and can serve as a starting point for further study of the nutritional requirements of sea bass larvae.

Effect of lipid level in a compound diet on the development of red drum (Sciaenops ocellatus) larvae.

Red drum larvae were fed, from day 11 to day 24 post-hatch, with Artemia (LP group) or two isoproteinic-formulated diets with varying lipid levels, 15% (L15 group) and 30% (L30 group). The lipid fraction was composed of a mixture of cod liver oil and soy lecithin. Larvae fed Artemia exhibited the greatest length; L30 diet induced a larvae length significantly greater than that obtained with L15 diet (P<0.05). No difference was observed in larvae survival among the three dietary groups. The increase in dietary lipid concentration led to an increase in amylase and trypsin secretion levels in 24-day-old larvae. The pancreatic secretion level measured in L30 group was close to that of LP group, suggesting that the maturation of the pancreatic functions was normally developed. Red drum larvae fed the diet containing the higher lipid content (L30) exhibited a more developed brush border membrane digestion in the intestine than larvae fed L15 diet (P<0.05). Phospholipase A2 was stimulated by the increase of phospholipids in the diet, but no difference was observed for lipase between the two compound diet-fed groups; the LP group exhibited the lowest lipase activity. A plateau in lipase activity may have occurred in red drum larvae from 15% fat level in the diet, suggesting that the maximal lipase activity was reached with 12% neutral lipid in the diet. The positive effects observed with high dietary fat may be due to the phospholipid fraction of the lipid mixture used.

Sea bass (Dicentrarchus labrax) larvae fed different Artemia rations: growth, pancreas enzymatic response and development of digestive functions

Abstract Sea bass larvae were fed different rations of 1-day-old Artemia from day 16 until day 38: satiation (R1), one-half ( R 1 2 ), one-quarter ( R 1 4 ) and one-eighth ( R 1 8 ) of the satiation ration. Survival was not significantly different among the four groups; the higher the ration, the greater the growth. In the pancreatic segment, trypsin activity was directly related to food ration, whereas amylase activity was inversely proportional. Trypsin secretion increased with age earlier in R1 and R 1 2 groups than in the two highly restricted groups. R 1 8 maintained a high level of leucine-alanine peptidase (an intestinal cytosolic peptidase). The preservation at day 38 of high amylase and leucine-alanine peptidase levels, in highly restricted larvae, indicates a delay in the development of the adult mode of digestion.