Effect of the diet and growing conditions on the manifestations of cannibalism in the eastern freshwater shrimp (Macrobrachium nipponense De Haan, 1849)

Purpose. To study the effect of diet and water flow composition on the manifestations of cannibalism of shrimp Macrobrachium nipponense during rearing under controlled conditions. Methodology. The material for the work was shrimp fry with a length 2.0-3.5 cm and weight 1.5-3.0 g, caught in autumn 2016 in ponds of the lower reaches of the Dniester river. The shrimp were kept in tanks of the recirculation system with a volume of 0.3 m3. The temperature regime, light (period and intensity), and other environmental parameters were maintained in accordance with the specified parameters. Weighing was carried out on an AXISAD-50 electronic balance with an accuracy of 0.001 g. The length was measured with a ruler or with a caliper. In chronic experiments, two groups of shrimps were kept at the stocking density of 3 ind./L, temperature of 26-29°C and other equal conditions in tanks of a recirculating system. The diet of the first group consisted of animal food (bloodworm, fish, squid, snail, tubule, artemia), the second group was fed by plant feeds (cereals, vegetables, spinach, nuts, alfalfa, rice, chickpeas). Maturation of females in the second group was not observed. At the same time, cases of aggressive behavior were rare, and cannibalism was not observed, which ensured 100% survival. In the second series of experiments, shrimp were kept in fattening tanks at stocking density of 2 ind./L and a ratio ♂♂: ♀♀ - 1: 4. The diet of shrimp consisted of animal and plant feeds (1: 1). During the 30 days of the experiment, the water temperature was maintained at 26.0 ± 0.5 °C, the photoperiod was 12 hours light, 12 hours dark. Findings. The shrimp, which received animal food, grew faster. 20% of the females formed eggs. At the same time, their aggressiveness was high, which led to the loss due to injuries and cannibalism of 40% of the individuals. The shrimp, which received vegetable food, grew slower. Their final weight and size were significantly lower (P> 0.95) than those of shrimps of the first group with similar initial parameters. In the tank No. 1, a lateral flow of moderate force was created. Shrimps formed a sparse aggregation in the center of the tank avoiding the current. They did not take refuge, did not show aggression towards each other and did not protect their territory. In the tank No. 2, with similar conditions, there was no lateral flow. Shrimps were distributed evenly in the tank, took refuge and protected their territory, were aggressive towards other individuals, often entering into fights with them. With similar size and weight characteristics of shrimp in both cultivation variants (the difference is not significant P <0.95), no loss was observed in the first case, while it was 20% in the second case. Originality. For the first time, it was shown that the diet composition affects the growth, behavior and survival of M. nipponense shrimp. The use of vegetable feeds reduced aggressiveness and improved shrimp survival. Animal food increased the intensity of growth, ensured maturation of females, but increased the loss of shrimp due to cannibalism. Cultivation of shrimp in a tank with lateral flow of moderate force reduced traumatism and the loss of individuals due to aggressive behavior, with similar size and weight parameters. Practical value. Shrimp Macrobrachium nipponense is a promising object of aquaculture in the southern Ukraine. Increasing the yield of marketable production is an important aspect ensuring profitability of production. In this regard, the development of the methods, which allow reducing aggressiveness and increase the survival of shrimps in conditions of marketable cultivation is of great practical importance.