Replacing live foods with microencapsulated diets in the rearing of seabass (Lates calcarifer) larvae: do the larvae ingest and digest protein-membrane microcapsules?

Abstract

Seabass larvae were fed all-protein-membrane microcapsules from first feeding, either alone or together with rotifers. To investigate ingestion and digestion, anaesthetized larvae that had been fed fluorescent microcapsules were examined under a confocal scanning laser-microscope. The passage of the microcapsules could be followed under continuous scan. Microcapsules were ingested by the larvae from first feeding. Although microcapsules from 15 μm to 150 μm were provided to the larvae, those ingested were 40-60 μm and took less than 60 min to pass through the gut. When only larger size microcapsules (80-150 μm) were provided, passage time was extended to more than 2 h because the microcapsules passed through the intestino-rectal valve with difficulty. All larvae fed microcapsules alone had died by the 10th day after hatching. The fluorescent protein wall of the microcapsules was not broken down in the larval intestine and the microcapsules passed through the rectum intact. Larvae fed microcapsules together with rotifers for 5 days and then microcapsules alone for 1 week had a mean survival rate of 2.4%. There was evidence that the protein wall of the microcapsules was broken down in the larval intestine when rotifers were present and that the protein membrane was absorbed. © 1991.