Description: Effects of moderate hypoxia and oscillating oxygen conditions on growth of European sea bass (Dicentrarchus labrax L.) were investigated. Groups of four to six sea bass (initial weights 40–90 g) were exposed to one of three oxygen regimes (40% air saturation; oscillations between 40–86% with a period of 770 min; 86% as a control) at 22°C and a salinity of 37 for 1 month. All fish survived and gained weight, but relative to the controls, the sea bass exposed to hypoxic conditions consumed significantly less food, exhibited a reduced growth, and had a lower condition factor. Oscillating groups were intermediate, and not statistically distinguishable from either normoxic or hypoxic treatments. Feed conversion efficiency and variation in body size were not significantly affected by oxygen conditions. Growth was correlated with feed intake, suggesting that reduced growth under moderate hypoxic or oscillating oxygen conditions is primarily due to reduced appetite and not a consequence of a decrease in feed conversion efficiency.

Description: Somatic growth and nucleic acid content were studied in North Sea houting Coregonus oxyrhinchus larvae fed exclusively on dry diets at 2 temperatures (8.4 and 17.5°C) during a 32 d rearing experiment. The higher temperature enhanced growth significantly. Mean dry weights at the end of the experiment were 3.6 mg (SD = 1.07, range 1.4 to 5.7 mg) and 31.5 mg (SD = 21.9, range 3.6 to 96.0 mg), and mean standard lengths were 17.7 ± mm (SD = 1.6, range 11.8 to 19.6 mm) and 25.5 mm (SD = 4.2, range 17.0 to 35 mm), respectively. Significant responses to temperature were also found in the nucleic acids. However, these differences were not as remarkable and gave indications that differences in protein growth between treatments was based on protein biosynthesis being driven by the activity of the ribosomes, rather than their number. The use of the degree-day approach to normalize the data clearly showed the temperature-dependence of somatic growth. Only small differences in growth and nucleic acid content were observed in the comparable range of the first 280 degree-days in fed fish. In non-fed fish, the starving potential was very similar (approx. 350 degree-days). Shifts in growth pattern from predominantly hyperplasia to predominantly hypertrophy were detected, with ongoing growth at both temperatures.

Description: A total of 354 adult European smelts Osmerus eperlanus (L.) were tested for their ability to survive the screen system of the cooling water inflow of a power plant. With increasing number of musculature parasitic third-stage larvae of Pseudoterranova decipiens, the survival rate of O. eperlanus decreased while the total number of externally visible injuries as well as the number of seriously injured specimens increased. The results indicate that even a single specimen of P. decipiens influences resistance and stamina and affects overall mortality of 7 to 20 cm long smelts. The initial effect of the parasites is to reduce swimming speed of infested fish, which leads to more frequent contact of these fish with the fine meshed screen of the cooling water inlet before they are removed by the automatic cleaning system. If the separated fishes are returned to the main stream, it becomes apparent that the cooling water inflow selectively reduces the number of living parasitised smelt in the area. Thus, the number of parasitic third-stage P. decipiens larvae in the local smelt population which are able to complete their life-cycle is also reduced. P. decipiens makes infested smelt more susceptible to negative anthropogenic influences such as cooling water intake or trawl fisheries.

Description: This study determined the effects of two test diets — a dry-phytoplankton and a trout-fry feed — and a control diet (Artemia nauplii) on tryptic activity, growth and survival rates during early life stages of Nile tilapia (Oreochromis niloticus) larvae. In addition, during a second experimental series, the interaction between trypsin and CCK (cholecystokinin) secretion was monitored in larvae fed with a PHA (phytohemagglutinin, a protein extract from the red kidney bean) enriched commercial trout-diet and compared with the data resulting from the use of the same but non-enriched feed. Subgroups were taken from the experimental units and kept under starvation. Oreochromis niloticus was chosen as a model species, since the larvae are able to intake artificial diets by the time of first feeding, and thus featuring the experiments with a manipulated micro-diet. The results demonstrated that larval mortality and growth are affected by the diet given and this was mostly observed in the group fed on dry-phytoplankton (12.2% mortality, 1.45 mg/d; control group: 2.9% mortality, 3.19 mg/d). The same larval group showed also a higher tryptic activity compared with all the other groups, which in combination with the bad survival and poor growth performance gives evidence for inadequate nutritional quality of the dry-phytoplankton feed for larvae aged more than two weeks after hatching. Every other feeding group showed good growth rates (trout-fry feed: 3.04–3.19 mg/d, with PHA enriched trout-fry feed: 2.85 mg/d), similar to the larvae fed with live prey (3.19–3.35 mg/d). A reduction of tryptic activity characterised the starvation process. These results confirm the usefulness of monitoring the individual tryptic activity as an indicator for evaluating the quality of a diet and the nutritional condition of fish larvae, but also the necessity of combining data of tryptic activity with growth and survival data for a correct interpretation. An interaction between trypsin and CCK secretion was also confirmed with this experimental approach, since induction and reduction of tryptic activity followed a reverse pattern compared with the concentration of CCK.