Cryogenic Sperm Banking of Mrigal ( Cirrhinus cirrhosus ) for Hatchery‐Scale Quality Seed Production in Bangladesh

The mrigal carp ( Cirrhinus cirrhosus ) has the highest demand in Bangladesh aquaculture due to its rapid growth, easy culture technology, customer preferences, and adaptability. But the quality of its seeds has declined over time in hatcheries. To ensure high‐quality and consistent seed production for aquaculture, sperm cryopreservation is a necessary technology to establish a sperm repository for this fish species. The goals of the study were to standardize the cryopreservation protocol and to establish a quality broodstock‐sourced sperm repository to produce high‐quality seeds at hatcheries. Broodstocks for sperm collection were produced by rearing Padma and Halda rivers‐origin juveniles. Sperm motility activation was evaluated in NaCl solutions with different osmolalities. Sperm exhibited the highest motility (94 ± 2%) and motility duration (40.2 ± 0.5 min) in 0.4% NaCl (128 mOsmol/kg). The toxicity of cryoprotectants (dimethyl sulfoxide [DMSO] and methanol) to sperm was tested at different concentrations (5%, 10%, and 15%) and incubation times (0–40 min) with two extenders (Alsever's solution and egg‐yolk citrate). Alsever's solution with 10% DMSO performed best with 95 ± 2% equilibration and 91 ± 2% post‐thaw motility at 1:9 milt to diluent ratio. A 10‐min equilibration produced the highest equilibration motility (92 ± 2%), while the samples cooling at 10°C/min resulted in highest post‐thaw motility (88 ± 2%). Breeding was conducted in 11 selected government and private hatcheries; using cryopreserved sperm from this sperm repository yielded an average fertilisation of 38 ± 2% and a hatching rate of 30 ± 2%. Fresh sperm yielded an average fertilisation of 77 ± 4% and a hatching of 66 ± 5%. Therefore, the utilization of cryopreserved sperm from the sperm repository was shown to be an effective method for seed production in this species. Although the process can be improved, sperm cryopreservation technology can be employed in commercial hatcheries, particularly for the generation of much‐needed quality brood fish.