Influence of lipid composition of live feed on growth,survival and pigmentation of turbot larvae

The effect of different lipid compositions of live feed on the survival, growth rate and pigmentation success of turbot larvae, Scophthalmus maximus (L.), was investigated. Rotifers, Brachionus plicatilis, together with the algae Tetraselmis sp., were administered until day 12, and Artemia was fed until day 27. The experimentally treated live feeds were enriched with four formulated emulsions, resulting in a gradient in the relative contents of 3 HUFA (highly unsaturated fatty acids) and in DHA (docosahexaenoic acid, 22:6 3)/EPA (eicosapentaenoic acid, 20:5 3) ratios in both the rotifers and Artemia.There were no differences in larval growth rate, and only small differences in survival rate throughout the feeding experiment, probably because of satisfactory levels of 3 HUFA in the live feed to sustain growth and survival. A correlation was obtained between the percentage of completely pigmented 27 d old turbot and the DHA/EPA ratio in the total lipids of 12 d old larvae, which again was correlated with the corresponding ratio in the live feed used. The results suggest that normal pigmentation in turbot requires dietary DHA in the early larval feeding period, and that this requirement cannot be replaced by EPA.     

Effect of seawater temperature on leucocyte populations in Atlantic salmon post-smolts

Using monoclonal antibodies (mAb) and flow cytometry, the distribution of immunoglobulin positive (Ig+) cells and neutrophils in isolated peripheral blood leucocytes (PBL) and head kidney leucocytes (HKL) from Atlantic salmon under-yearling out-of-season smolts was studied in the post-smolt period from 0 to 14 weeks after seawater transfer. A temperature acclimation was performed in freshwater, resulting in four groups maintained at a water temperature of 18, 14, 10 and 6 degrees C, respectively. The temperature for each group was kept constant for the remaining period and all groups were reared under a simulated natural photoperiod regime (60 degrees 25'N). Sampling of eight fish from each temperature group was performed at regular intervals from 0 to 14 weeks after seawater transfer, starting the day after transfer (week 0). The seawater temperature influenced the distribution of the leucocyte populations, and the effect was most prominent in PBL. The lower rearing temperature (6 degrees C) resulted in higher percentages of Ig+ cells in PBL compared to fish reared at the other temperatures. The high temperature (18 degrees C) resulted in higher proportions of neutrophils and lower proportions of Ig+ cells in PBL compared to fish from the other temperature groups. The observed differences were consistent throughout the 14-week experimental period. While the present study indicate that rearing water temperature influence the distribution of leucocytes in blood of Atlantic salmon post-smolts, the proportions of HKL populations do not seem to be dependent on temperature to the same extent. Comparing the temperature groups, no clear differences in the percentages of Ig+ cells and neutrophils in HKL were observed. Likewise, no evident time-related changes in the leucocyte profiles within each temperature group could be observed during the studied post-smolt period. Significantly, the results could indicate that the post-smolts reared at a temperature of 18 degrees C experienced thermal stress or a non-optimal environment.