Evaluation of larval quality of viviparous scorpionfish Sebastiscus marmoratus

The aim of this study was to develop an acute test for larval quality in the viviparous scorpionfish Sebastiscus marmoratus. Rearing experiments until day 13 post parturition were conducted to investigate the survival of larvae for 13 different batches, and tolerance to starvation of larvae was examined and expressed by the survival activity index (SAI). The morphological characters, enzyme activity, and swimming behavior of larvae on day 0 and 1 were also observed, followed by the correlation analysis between SAI. Larvae with high SAI (?26) showed significantly higher survival on day 13 than larvae with low SAI, which confirmed that SAI is a reliable index that can be used to evaluate larval quality, similar to the former findings. The esterase activity (r = -0.713, P < 0.01), swim frequency (r = -0.735, P < 0.01) and swimming speed (r = -0.588, P < 0.05) of larvae on day 0 were significantly and negatively correlated with SAI. It was concluded that enzyme activity and behavioral characters of larvae just after parturition can be a real-time index for evaluating the larval quality of this species

Evaluating the nutritional condition of individual whitefish (Coregonus spp.) larvae by the RNA/DNA ratio

Larvae of Coregonus spp. were reared in the laboratory under different temperature (4,6 and 8°C) and feeding conditions (ad libitum, limited, with starvation intervals). Their RNA/DNA ratios were determined with a highly sensitive fluorescence technique. After resorption of their yolk reserves (about 2 weeks after hatching), well fed larvae (RNA DNA> 2·5) could he significantly distinguished from larvae reared under limited food supply (RNA DNA < 25), both at the 6 and 8°C levels. At 4°C no differences due to the feeding regime were found. During a second series of experiments, larvae were affected by an intestinal disease, which was caused hy the ingestion of unsuitable copepod plankton. This disease provoked high mortality, decreased growth and RNA DNA ratios which were almost as low as in temporarily starved larvae from the first series. Corcgouid larvae sampled in Lake Constanee during spring 1990 showed RNA· DNA ratios which were unexpectedly low when judged on the basis of mean body length and average ambient temperature. It was obvious from macroscopic observations that some of these WIld larvae were severely attacked hy the intestinal disease. The low RNA-DNA ratios in field samples arc, therefore, interpreted as a sublethal result of this disease