Evaluation of Starvation Status of Laboratory-Reared Japanese Flounder Paralichthys olivaceus Larvae and Juveniles Based on Morphological and Histological Characteristics

Japanese flounder Paralichthys olivaceus larvae and early juveniles were reared for 43 days after hatching in order to observe the effects of starvation during development and metamorphosis. Morphological and histological measurements were made to assess the nutritional status during growth and starvation from prematamorphic through postmetamorphic phases. Two groups of fish were compared; one with sufficient food supply and one under continuous starvation until death. The activity changes of fish during starvation were also observed. Among morphometric analyses, both ratios of body height at anus/head height and pre-/postanal lengths appeared to be sensitive to starvation during which substantial reduction was observed within a day of food deprivation. Starved fish gradually decreased swimming speed as starvation proceeded and finally stayed motionlessly on the tank bottom. Histological variables as intestinal and rectal epithelial heights and gall bladder volume changed significantly with onset of starvation. The gut epithelial heights of starving fish decreased with advances in starvation, although they fluctuated during the mid-metamorphic phase. In contrast, gall bladder volume increased remarkably soon after starvation. Ontogenetic changes in both gut epithelial height and gall bladder volume were evident, those associated with settlement and/or completion of metamorphosis. These findings suggest that a combination of morphologically and histologically sensitive characteristics could be utilized as a reliable measures to evaluate the nutritional status related to starvation in wild Jaoanese flounder larvae.