Evaluation of the suitability of plant and textile substrates as attachment surfaces for mirror carp eggs during induced spawning by environmental simulation
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The efficiency of plant and textile substrates (cotton sheets, gunny bags, papyrus umbels, and banana leaves) for efficient induced breeding of Mirror carp by semi-natural method was investigated. The study was carried out at Buginyanya Zonal Agricultural Research and Development Institute-Bulegeni Satellite station. Breeders were conditioned for three months during which they were fed on Kajjansi sinking feeds (35% crude protein) at a rate of 3% body weight two times a day. Specimens comprised 48 ripe breeders, with a mean weight of 1.1±0.1kg (males) and 1.3±0.3 kg (females) which were selected and stocked in a sex ratio of 1 female: 2 males in breeding ponds (10×10 m) with submerged substrates. After spawning, substrates with attached eggs were transferred to hapas suspended in a pond for incubation and primary nursing. Fecundity, fertilization rate, hatching rate, survival rate, and water quality parameters were assessed during the study period. Spawning took place overnight and was preceded by courtship behaviors like chasing and nudging. Papyrus umbels stimulated release of the highest number of eggs (1677 eggs kg-1) and gave fairly a good hatching rate (40.8%), compared to other substrates. Banana leaves stimulated the release of a relatively high number of eggs (1471 eggs kg-1), however the hatching rate was very low (15.7%). The gunny bags gave a fairly good hatching rate (36.5%), however fecundity was very low (701 eggs kg-1). Cotton sheets stimulated low fecundity (623 eggs kg-1) and hatching rate (18.5%). The fertilization and survival rates did not differ significantly among the treatments (p>0.05) and varied between 79.4%-84% and 24.4%-29% respectively. This study suggests that plant substrates induced more spawning compared to textile substrates due to their brown color which is attractive to carps while the hatching rate is related to the floating ability of the substrates which allows sufficient aeration of the eggs. Papyrus umbels are more suitable substrates in semi-natural propagation of mirror carp, since they stimulated release of the highest number of eggs and gave a fairly good hatching rate.