Author(s): Nafia Binte Ryhan, Md. Rafiqul Islam Sarder, Md. Fazlul Awal Mollah, Md. Salah Uddin Kabir, Mohammad Matiur Rahman and Md. Shariful Islam

Abstract: Cryogenic gene banking is a prime necessity for conserving the genetic constitutes of vulnerable, endangered and critically endangered native and exotic fish species. Cryogenic freezing of fish gametes is the first step to develop such a gene bank. In the study, attempts have been taken to develop a cryogenic freezing protocol of spermatozoa of Mohashol, Tor tor as it is considered as a critically endangered fish species by IUCN. Juvenile and brood fish of Tor tor were collected from the Someshwari River of Netrokona district and domesticated in captive condition at Bangladesh Agricultural University campus. During breeding season, sperms were collected from hormone induced males by stripping. The milt was very sticky. The concentration of sperm was 4.47 x 10¹⁰ cells per ml and pH was 8.6±0.5. The sperm demonstrated Brownian and forward movement during motility. Activation of sperm motility has been evaluated in different concentrations (0.1% to 1.0%) of activation solution (NaCl) and found that sperm motility decreased with increasing concentration of NaCl. Motility of sperm at 0.4% NaCl was more or less stable and completely activated. Sperm motility was completely inhibited at 1.0% NaCl. A significant difference (p = 0.001) was observed between the complete activation and inhibition of sperm at 0.4% and 1.0% NaCl solution respectively. Though cryopreservation of sperm of Tor tor has been possible through this study, no breeding trial was conducted due to lack of ovulated eggs. So far it is the first cryopreservation work of Tor tor and more research work needs to be done to develop the complete protocol for ex-situ conservation of this examined fish species.

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