Drinking and Na super(+)/K super(+) ATPase activity during early development of European sea bass, Dicentrarchus labrax Ontogeny and short-term regulation following acute salinity changes

The short-term osmoregulatory capacity of sea bass (Dicentrarchus labrax) larvae and juveniles at consecutive developmental stages was evaluated by an analysis of drinking rates and whole-body and branchial Na super(+)/K super(+) ATPase activity. The effect of acute salinity stress on those parameters was assessed from hatching to the juvenile stage. Drinking rate normalised to body weight (DR sub(bw)) decreased throughout postembryonic development. DR sub(bw) was not affected by salinity in yolk sac larvae. However, significant differences were observed in older larvae and in juveniles submitted to hypo-and hyperosmotic challenges. Post yolk sac larvae and juveniles always drink, but at a lower rate in hypoosmotic media compared to hyperosmotic media. A correlation was established between DR sub(bw) and blood osmolality during the postembryonic development of the sea bass. Na super(+)/K super(+) ATPase specific and total activity in whole larval homogenates decreased from hatching to the 5-mm yolk sac larva stage and increased in 10-mm stage larvae. The enzyme specific activity in the gills, from post yolk sac larvae to juveniles, decreased whereas the total activity increased during the same period. Developing sea bass have a better capacity to cope with hypoosmotic than hyperosmotic media.