WEIGHT GROWTH AND SURVIVAL CRAYFISH OF DIFFERENT SPECIES DEPENDING OF THEIR STOCKING DENSITY
The aim of the research. Investigate the effect of crayfish planting density of different species on their weight growth and population survival.
Materials and methods of research. The research was conducted in the Aquaculture Laboratory of the Polissya National University. To conduct the experiment, 3 groups of 12-month-old crayfish of Australian red claw, Cuban marble, red swamp and noble crayfish species were formed, numbering 10, 20 and 30 individuals of each species. 50% of males and 50% of females were selected from the group.
Hydrobionts of each group were kept separately in tanks with an area of 0.65 m2. There were a total of 12 aquariums, the water temperature in which, according to the method of T. Abeel et al., was 25ºC, pH of water – 7ºT, oxygen content – 7 mg/l. The water quality was acceptable and the same for all test species, it was filtered using mechanical and biological filters.
Research results. It was established that the density of planting in the broodstock significantly influenced the weight growth of crayfish. Thus, the live mass of Australian redclaw crayfish species at stocking densities of 20 and 30 heads/m2 was lower compared to individuals whose stocking density was 10 heads/m2, respectively by 0.8 (P < 0.001) and 3.4 (P < 0.001), Cuban marble – by 0.9 (P < 0.01) and 1.7 (P < 0.001), red swamp – by 2.2 (P < 0.001) and 3.2 (P < 0.001) and noble crayfish – by 2.0 (P < 0.01) and 5.5 g (P < 0.001).
Variability of live mass, depending on crayfish species and stocking density, ranged from 1.7 to 6.4%, with the highest variation in red swamp species and the lowest in Australian redclaw crayfish. Average daily increases were characterized by much greater variability - from 20.7 to 32.1%.
Crayfish stocking density also had a significant impact on the level of cannibalism and stock preservation. It should be noted that the largest number of lost limbs was noted in individuals of the noble species. At the maximum planting density (30 heads/m2), the loss of limbs was 76.7%, and at a planting density of 20 heads/m2 – 55.0%, which is 46.7 and 35% more than that of the crayfish of the first group. 0% respectively. The smallest number of lost limbs was observed in individuals of the marble species at a planting density of 10 heads/m2. According to this indicator, they were inferior to hydrobionts of the second and third groups by 20.0 and 33.3% (P < 0.01). The crayfish of the first group of the Australian redclaw species were inferior to individuals of the second and third groups by 20.0 and 33.3%, and the red swamp species – by 15.0 and 26.7%, respectively.
Regarding the preservation of the crayfish population at different planting densities, it should be noted that with an increase in the number of individuals per 1 m2, their survival rate decreased. In the first group, the highest death rate was observed in crayfish of the Australian redclaw and noble species – 2 heads each. Among individuals of the red swamp and marble species, 1 individual died each.
At a stocking density of 20 heads/m2, survival of the crayfish population decreased significantly: in individuals of the Australian redclaw by 15.0, marble and red swamp by 5.0, and noble crayfish by 20%.
At the maximum stocking density, marble crayfish were characterized by the highest population preservation – 76.7%, and noble crayfish – the lowest (43.3%). At the same time, the difference in this indicator between the hydrobionts of all species of the third and first groups (with the exception of the marble species) was significant and amounted to 24.3 (P < 0.05) for the Australian redclaw crayfish, 13.3 for the marble crayfish, and 13.3 for the red swamp crayfish – 16.7 (P < 0.05) and noble – 37.7% (P < 0.01).
Conclusions. The density of their landing has a significant effect on the live weight and preservation of the crayfish population of various species. At the maximum planting density of hydrobionts, a significant decrease in the survival of individuals was observed, while their live weight and average daily growth probably increased, which is obviously explained by the crayfish eating dead individuals in addition to the given feed.
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