Assessment of Growth, Lipid Metabolism and Gene Expression Responses in Senegalese Sole Larvae Fed With Low Dietary Phospholipid Levels

Effects of enrichment of live prey with soy lecithin on growth, stress resistance, digestive enzymes activity, and antioxidant capacity in yellowfin seabream (Acanthopagrus latus) larvae

Phospholipid (PL) is an essential nutrient that has vital effects on growth, stress resistance, and early development in marine fish larvae. In this regard, a 30-day feeding experiment was conducted in order to examine the effects of live prey enrichment with graded levels of soy lecithin (SL) on some physiological responses of Acanthopagrus latus larvae. Four experimental emulsion levels of SL were used to enrich rotifer and Artemia including very low (2%, N-Nil), low (4%, L), medium (8%, M), and high (12%, H). Newly hatched larvae were distributed into 12,250-L cylindrical tanks with an initial density of 15,000 larvae in each tank that was supplied with natural seawater (23 ± 1°C; 40.0 ± 1.0 g L-1). Larvae fed live prey enriched with 4% SL significantly had higher wet weight gain than other treatments. Air exposure and osmotic activity tests were also performed to detect larval resistance to stress. Larvae fed live prey enriched with 8% and 12% SL had higher survival compared to the other two groups. The accumulation of arachidonic (ARA) and docosahexaenoic acid (DHA) was increased in the whole body of larvae fed high SL-supplemented live prey. Alkaline phosphatase and aminopeptidase N activities in the guts brush border membrane of larvae in M and H groups were higher than other treatments. The trypsin and chymotrypsin activities in the N group were lower than in other groups. The highest and lowest amylase activities were in the H and N groups, respectively. The activity of catalase in the whole body of the M group was higher than the N group and the glutathione reductase activity was significantly increased in the M and L groups compared to the N and H groups. Total antioxidant capacity in the whole body of larvae in the N group was lower than in the other treatments. In summary, moderate levels of SL (4%-8%) are suggested for the enrichment of live prey in A. latus.

Dietary Phospholipids Enhance Growth Performance and Modulate Cold Tolerance in Meagre (Argyrosomus regius) Juveniles

Simple Summary

Meagre is a target species to diversify marine aquaculture in Europe due to its high growth rates and an excellent nutritional profile. Nevertheless, this species is highly sensitive to low temperatures. The objective of this study was to evaluate the effect of dietary phospholipid (PL) levels on growth and cold tolerance. Animals fed with a PL-enriched diet grew faster and significantly reduced the risk of death and increased the lethal doses 50 and 90 without modifying the average temperature at death. Regarding lipid profiles, the cold challenge promoted a general fatty acid accumulation in the liver that was attenuated in fish fed with the PL-enriched diet preventing the negative effect of a fatty liver.

Abstract

Meagre (Argyrosomus regius) is a fast-growing species currently produced in aquaculture. This species is highly sensitive to low environmental temperatures which results in high mortality events during production cycles. In this study, the effects of dietary phospholipids (PLs) on growth and cold tolerance were evaluated. For this purpose, control (CTRL) and PL-enriched diets (three-fold higher levels than CTRL) were supplied to meagre juveniles (12.9 ± 2.5 g) for 60 days, and growth was determined using a longitudinal approach. Weight gaining and SGR reduction were significantly different between dietary treatments. Animals fed with the PL-enriched diet were 4.1% heavier and grew 3.2% faster than those fed with the CTRL diet. Survival was higher than 98% in both groups. After finishing the growth trial, animals were submitted to two cold challenges and cold tolerance was evaluated as temperature at death (Tdeath), risk to death and lethal doses (LD) 50 and 90 using the cumulative degree cooling hours 6 h (CD6H). Tdeath ranged between 7.54 and 7.91 °C without statistical differences between dietary treatments. However, risk to death was significantly smaller (0.91-fold lower) and LD50 and LD90 were higher in animals fed with the PL-enriched than those supplied the CTRL diet. To assess the fatty acid (FA) composition of liver and brain in animals fed both diets after a cold challenge, FA profiles were determined in juveniles maintained at 14 °C and challenged at 7 °C. FA amounts increased in the liver of animals challenged at 7 °C. In contrast, several FAs reduced their levels in the PL-enriched diet with respect to CTRL indicating that these animals were able to mobilize efficiently lipids from this organ mitigating the negative effects of lipid accumulation during the cold challenge. In brain, the PL-enriched diet increased DHA level during the cold shock indicating a role in maintaining of brain functions. These results open a new research line that could improve the cold tolerance of meagre through dietary supplementation before winter.