56 SEPTEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG Artemia was 21.7 mg. At this stage, mortality of the feeding larvae fed with yolk was 16 percent and with Artemia was 12 percent. After resorption of the yolk sac, larvae eating chicken yolk began to lag behind in growth and by the end of the experiment their weight was 43.2 mg, while the weight of larvae grown on Artemia was 68.4 mg. Mortality of larvae fed chicken yolk was 74 percent, which was twice as much as the other group. River perch larvae have a strong reaction to moving objects because vision plays an important role in feeding behavior. To improve the efficiency of cultivation of perch, early larvae on the next phase of work, we conducted a study of the influence of the duration of the photoperiod on the growth and survival of feeding larvae (Fig. 4). Increasing the duration of the photoperiod resulted in increased growth and survival of larvae. When the ratio of light to dark hours was 12:12, survival rate was 36 percent and biomass density was 3.7 g/L. Increasing the photoperiod to 16 hours resulted in a decrease of mortality to 33 percent and the biomass density of larvae increased 2.2 times. This confirms the importance of vision in the feeding behavior of perch in the early stages, subject to the availability of feed in the water. At night, with the cessation of feeding, lights must be turned off because, in the absence of feed particles, larvae start to swallow small air bubbles from the water surface in aquaria with aeration, leading to an accumulation of air in the intestines. The phenomenon is not widespread but it causes the weakening of the body and cessation of feeding. When the intestines are filled completely with air, the larvae die. Special attention at the early stages of larval development is required because of the emergence of cannibalism. In cultivation of predatory species of fish at high stocking density, this phenomenon has a great influence on production. Cannibalism begins to occur 1012 days after active feeding, when some larvae begin to lag behind in growth. Figure 5 indicates the main size groups of perch larvae. The primary size group (60-70 mg) is represented by the largest number of individuals (48 percent of the total). The largest specimens weighed 100 mg or more and the smallest were 10-20 mg, representing less than 10 percent. On the other hand, with increased weight of individuals the percentage of cannibalism appears to rise in the group. Among the biggest perch, more than 21 percent were cannibals. In one group of individuals, the rate of cannibalism was below 6 percent. To prevent cannibalism, growing larvae should be sorted. This helps to reduce the loss to 1-2 percent. There was almost no difference in the level of cannibalism at different densities. Losses from cannibalism are normally 1214 percent. Therefore, as a practical proposition, density of early juvenile perch at 100/L is recommended. In the course of the research in the conditions of Aquabiotechnopark, the main stages of larval development of Eurasian river perch were established and some of the conditions for the efficient keeping and rearing of larvae were identified. The best fish production and biological indicators were observed in early larvae that consumed live prey after resorption of the yolk sac. The optimum photoperiod regime was 16 hours light and 8 hours dark. Experiments proved that the increase in cannibalism depends on the size variation of individuals in a population. In other words, the greater the variation in individual size, the greater the percentage of cannibalism. Notes Fedorovykh, Yu.V.,S.V. Ponomarev and Yu.M.Bakaneva, Astrakhan State Technical University, Astrakhan, Russia E mail: jaqua@yandex.ru 1 Statistics and analytics of water bioresources catches in Russian Federation water bodies, 2010. (fish.gov.ru/otraslevayadeyatelnost/ekonomika-otrasli/statistika-i-analitika). References Carasciuc, A.V. and S.P. Petrichenko.2006. Mass composition and survival ability of perch and cyprinid fishes. Journal of Fishery 4:68-69 Eckmann, R. and F.Imbrock.1996. Distribution and vertical migration of Eurasian Perch (Perca fluviatilis L.) during winter. Annales Zoologici Fennici 33:679-686. Jankowska, B., B. Jankowska, Z. Zakes, T. Zmijewski, M. Szczepkowski andA.Kowalska. 2007. Slaughter yield, proximate composition, and flash colour of cultivated and wild perch (Perca fluviatilis L.). Czech Journal of Animal Science 52(8):260-267. Konstantinov, K.G. 1957. Comparative analyses of morphology and biology of perch and pike perch on different stages of FIGURE 5. Cannibalism during the early stages of ontogenesis of river perch. (JUMP TO PAGE 72) FIGURE 4. Effect of photoperiod on growth and survival of river perch larvae.
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