~ 320 ~ International Journal of Fisheries and Aquatic Studies 2021; 9(4): 320-326 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2021; 9(4): 320-326 © 2021 IJFAS www.fisheriesjournal.com Received: 19-05-2021 Accepted: 21-06-2021 Nafia Binte Ryhan Lecturer, Department of Fisheries, Faculty of Agriculture, EXIM Bank Agricultural University, Nawabganj, Bangladesh Md. Rafiqul Islam Sarder Professor, Department of Fisheries Biology and Genetics, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh Md. Fazlul Awal Mollah Professor, Department of Fisheries Biology and Genetics, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh Md. Salah Uddin Kabir Ph.D. Fellow, Department of Fisheries Biology and Genetics, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh Mohammad Matiur Rahman Professor, Department of Fisheries Biology and Genetics, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh Md. Shariful Islam Senior Scientific Officer, Bangladesh Fisheries Research Institute, Freshwater Sub- Station, Chanchra, Jashore, Bangladesh Corresponding Author: Nafia Binte Ryhan Lecturer, Department of Fisheries, Faculty of Agriculture, EXIM Bank Agricultural University, Nawabganj, Bangladesh Evaluation of toxicity of cryoprotectant to the sperm of mohashol fish, Tor tor (Hamilton) at various concentrations of the salt solution Nafia Binte Ryhan, Md. Rafiqul Islam Sarder, Md. Fazlul Awal Mollah, Md. Salah Uddin Kabir, Mohammad Matiur Rahman and Md. Shariful Islam DOI: https://doi.org/10.22271/fish.2021.v9.i4d.2551 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 4.47x10 10 cells per ml and pH was 8.6±0.5. To evaluate the toxicity of cryoprotectant, sperm was incubated with DMSO and methanol at 5, 10 and 15% concentrations for a period of 5 to 55 min. The motility of sperm decreased with the increase of cryoprotectant concentration (5, 10 and 15%) and 10% DMSO with Alsever’s solution could be the best combination for cryopreservation of T. tor. sperm at 10 min (83.0±2.74). Keywords: toxicity, sperm motility, cryoprotectant 1. Introduction Bangladesh is enriched with numerous rivers, flood plains, low lands, haor, baor (ox-bow lakes), beels, lakes etc. The country is also enriched with endemic fish resources including 260 freshwater fishes and 24 prawn species, 16 exotic freshwater species; 475 marine fishes and 24 shrimp species (DoF 2016) [7] . Among 260 freshwater fish species of the country, 12 have been categorized as critically endangered, 28 as endangered and 14 as vulnerable (IUCN Bangladesh 2015) [11] and stocks of some fish species have been depleted to below replaceable levels. Conservation programs require large populations to ensure biodiversity but for threatened and endangered species the numbers of fish are steadily decreasing. Cryopreservation can help in both of these situations. Cryopreservation is a process by which biological cells or tissues are preserved at subzero temperatures resulting in a radical decrease in the rate of metabolic processes and the ability to store samples for extended periods (Armitage 1987) [1] . The availability of frozen sperm is a proven technique for developing, maintaining, and distributing genetic improvement in livestock, and provides great unexploited potential for fish breeding. Fig 1: Mohashol, Tor tor (Hamilton 1822)