Wolska-Neja B., Neja Z. 2006. Grow-out of northern pike (Esox lucius L.) larvae under uncontrolled conditions.Acta Ichthyol. Piscat. 36 (2): 105-112.
Background. This study aimed to determine survival rate, extent of cannibalism, and growth rate of northern pike (Esox lucius L.) larvae fed live zooplankton during a grow-out period, i.e., the time prior to when fish become valuable as stocking material. An attempt was also made to assess the food conversion ratio (FCR) with respect to the natural food applied.
Materials and methods. Grow-out operations began with 1-day-old pike larvae and involved experimental in-ground
tanks with no artificial aeration, forced water flow, artificial circadian lighting, or temperature control. Differently structured habitats (black polyethylene foil, vascular plants, or plastic netting) were placed in all the tanks to separate larvae and provide cover. Feeding live zooplankton to the larvae began on day 3 and food was administered such that larvae were always surrounded by a zooplankton "cloud."
Results. The survival rate during the first- (days 1-7) and second (days 8-27) stage of culture was 92.3% and 95.7%,
respectively. Highest survival rates were associated with tanks with polyethylene foil habitats, while lowest survival rates were associated with tanks containing plastic netting. No cannibalism was observed in any tank. During the growout period, the total length of larvae increased by an average of 20.88 mm. Although the length increase observed in the three experimental treatments was similar; the significantly highest (P < 0.01) mean length (32.66 mm) was associated with larvae raised in tanks containing polyethylene foil. Until day 13, the mean weight of the larvae did not differ between the three treatments (P = 0.21). At and beyond day 20, fish kept in tanks equipped with polyethylene foil exhibited higher weight increments and on termination of the experiment the mean individual weight of larvae was significantly higher (P < 0.05) than those of larvae in tanks with vascular plants and plastic netting. The food conversion ratio, calculated for the entire culture period was 4.9.
Conclusion. High survival rate of the cultured pike larvae demonstrated the success of pike larvae grow-out under uncontrolled conditions.
Keywords: fish, pike, Esox lucius, larvae, larval grow-out, crustacean diet