Water flow requirements in the intensive production of Atlantic salmon ( Salmo salar L.) fry: growth and oxygen consumption

Abstract

Atlantic salmon ( Salmo salar L.) fry (1–10 g) were exposed to three water flow rates: 1.4 (control), 1.0 (medium) and 0.7 l kg −1 min −1 (low). There were four replicate tanks in each group. Alkalinity was low (0.03–0.04 mM). Oxygen was added to the inlet water to maintain discharge water oxygen concentration higher than 7 mg l −1, at 16°C. The mean weight of fish in the low water flow group was significantly lower than in the control flow group after 2 months. No significant differences in mean fish length and condition factor between groups were found. There was no significant difference in the frequency of occurrence of gill lesions among the groups. Mortality was low in all groups (0.3–0.4%). In the majority of tanks (nine of 12), oxygen consumption rates decreased significantly as the mean fish size increased. An overall range of 5–12 mg O 2 kg −1 min −1 was observed. There were no significant differences between the b-values (weight exponent: log oxygen consumption versus log body weight) of the three groups. The range of the weight exponents for the combined groups (between −0.19 and −0.23) was narrower than that of the individual tanks (between −0.12 and −0.27). The wide range in the individual tanks may be a result of relatively few oxygen measurements. No significant differences were found in the oxygen consumption levels of the three groups. The oxygen consumption rate was however higher than predicted by earlier oxygen consumption models. The mathematical corrections of oxygen consumption rates due to reaeration of oxygen were generally within ±3% of the measured oxygen consumption rates (in all tanks). Further studies are needed both to quantify water flow requirements and oxygen consumption rates for Atlantic salmon fry.