The effect of stocking density on the survival and growth of pikeperch, Sander lucioperca (L.), larvae was examined in two consecutive experiments. In experiment I, 4-day-old larvae [body wet weight (BW): 0.5 mg; total body length (TL): 5.6 mm] were reared in 200-l cylindro-conical tanks in a closed, recirculating system (20 ± 0.5°C) at three stocking densities (25, 50 and 100 larvae l -1 ) and fed a mixed feed (Artemia nauplii and Lansy A2 artificial feed) for 14 consecutive days. At densities of 25 and 100 larvae l -1 , growth rate and survival ranged from 2.7 to 1.9 mg day -1 and from 79.2 to 72.3%, and fish biomass gain ranged from 0.6 to 2.0 g l -1 , respectively. There were two periods of increased larval mortality: the first was at beginning of exogenous feeding and the second during swim bladder inflation. In experiment II, 18-day-old larvae (BW: 35 mg; TL: 15.6 mm) obtained from experiment I were reared under culture conditions similar to those of experiment I, but at lower stocking densities (6, 10 and 15 larvae l -1 ). The fish were fed exclusively with artificial feed (trout starter) for 21 consecutive days. At densities of 6 and 15 larvae l -1 , the growth rate and fish biomass gain ranged from 28.8 to 23.1 mg day -1 and from 2.0 to 3.3 g l -1 , respectively. The highest survival (56.5%) was achieved at a density of 6 larvae l -1 . Mortality at all densities was mainly caused by cannibalism II type behaviour (27-35% of total). In both experiments, growth and survival were negatively correlated and fish biomass gain positively correlated with stocking densities.

No abstract

No abstract

The aim of this study was to compare physiological responses in Siberian sturgeon (Acipenser baeri) induced by propofol and CO 2 anaesthesia. Two procedures were applied during the experiment. In procedure I, blood samples were collected immediately after exposure (1, 2, 5, 10 min) to the anaesthetic. In procedure II, fish were exposed to the anaesthetic for 10 minutes and then were moved to anaesthetic free water. Blood was sampled after 5, 10, 20 or 30 min of recovery time. Gasometrical and biochemical analyses were performed on collected blood.In CO 2 anaesthetized fish strong hypercapnic acidosis was revealed. The drop of the HCO 3 -/CO 2 ratio, from 28:1 in control fish up to 4:1 in CO 2 anaesthetized ones, proved that the compensation mechanism is not capable of preventing acidosis during CO 2 anaesthesia in Siberian sturgeon. In contrast, only moderate, respiratory acidosis occurred in sturgeons anaesthetised with propofol. Hypercapnic acidosis during CO 2 anaesthesia was followed by a fourfold increase of ammonia level in the blood. Glucose level, increasing only during recovery time, indicates that a secondary stress response occurred when awareness of anaesthetized fish had been restored.