Survival, development and food energy partitioning of nase larvae and early juveniles at different temperatures

Survival was generally high, 94 100%, for newly hatched larvae of the nase Chondrostoma nasus held at 10, 13, 16, 19, 22, 25 and 28 degrees C up to da y 66 post-fertilization. The developmental rate decreased with age and incr eased with temperature. Specific growth rates increased with temperature: w ithin one temperature range growth rate decreased with ontogenetic developm ent. Food consumption and respiration increased with temperature and body s ize. A temperature increase From 25 to 28 degrees C resulted in slightly re duced survival, minor acceleration of developmental growth and respiration rates, and impeded skeleton formation. Growth efficiency of consumed energy decreased throughout the larval period From 55 to 67% at the first larval stage (L-1) to 36-48% at the first juvenile stage (J(1)). A similar trend F or assimilation efficiency and its utilization for growth was observed. The constant temperatures required by larval nase ranged from a minimum 8-10 d egrees C to a maximum 25-28 degrees C. A shirt of optimum temperatures. 8-1 2, 13-16, 15-18, 19 and 22 degrees C for nase spawning, embryonic developme nt, yolk feeding larvae, early externally Feeding larvae and, late larvae a nd juveniles, respectively, paralleled the spring rise in the river water t emperature. Larval and juvenile nase show high survival, growth and energy conversion efficiencies compared with other fish species. On the other hand , low survival rates and growth can be attributed to external perturbations ; thus, young nase may be considered a good indicator or the environmental and ecological integrity of river systems. (C) 2001 The Fisheries Society o f the British Isles.