Ontogeny of the digestive system of meagre Argyrosomus regius reared in a mesocosm, and quantitative changes of lipids in the liver from hatching to juvenile

Abstract

Histological development of the digestive system was studied in association with feeding preferences in meagre (Argyrosomus regius) from hatching to juvenile (44days after hatching, dah), using a mesocosm system. In addition, the liver lipid content was evaluated using histological methods (area covered with lipid vacuoles, ACLV%). The ontogeny of the digestive system was completed by 19dah (or 444degree days) with the gastric glands appearing at 15dah (361degree days), the pyloric ceaca at 17dah (404degree days) and the Y-shaped stomach formed at 19dah (444degree days). The rearing period was characterized first by relatively slow growth until tail flexion (~15dah) and fast growth thereafter (mean±SD total length of 45.14±4.00mm at 44dah). When the feeding protocol included exclusively rotifers, mean ACLV remained low (2.39±0.34%) while feeding on Artemia nauplii and copepods increased liver ACLV to 47.18±6.56% at 20dah. Changes in the feeding protocol were reflected in feeding preferences (stomach content), and variations of liver lipid content and the occurrence of vacuoles in the intestine. During transition from live prey to artificial feed (~28dah), ACLV decreased significantly – indicating a malnutrition period – concomitant with a delay in the acceptance of artificial feed of 8 days. Thereafter, consumption of artificial feed resulted in an increased ACLV to 56.3±7.6% at 36dah. The results indicate that during early development meagre is a fast growing species, developing rapidly the structures and basic organs of the digestive system required to overcome successfully the critical stages of larval rearing. The study also shows that histological evaluation of liver lipid content using the ACLV may be a valuable tool in commercial aquaculture to improve larval rearing protocols, and production efficiency.