Genome size estimation and its associations with body length, chromosome number and evolution in teleost fishes.

Precise estimation of genome size (GS) is vital for various genomic studies, such as deciding genome sequencing depth, genome assembly, biodiversity documentation, evolution, genetic disorders studies, duplication events etc. Animal Genome Size Database provides GS of over 2050 fish species, which ranges from 0.35 pg in pufferfish (Tetraodon nigroviridis) to 132.83 pg in marbled lungfish (Protopterus aethiopicus). The GS of majority of the fishes inhabiting waters of Indian subcontinent are still missing. In present study, we estimated GS of 51 freshwater teleost (31 commercially important, 7 vulnerable and 13 ornamental species) that ranged from 0.58 pg in banded gourami (Trichogaster fasciata) to 1.92 pg in scribbled goby (Awaous grammepomus). Substantial variation in GS was observed within the same fish orders (0.64-1.45 pg in cypriniformes, 0.70-1.41 pg in siluriformes and 0.58-1.92 pg in perciformes). We examined the relationship between the GS, chromosome number and body length across all the fishes. Body length was found to be associated with GS, whereas no relationship was noticed between the GS and the chromosome number. The analysis using ancestral information revealed haploid chromosome number 25, 27 and 24 for the most recent common ancestor of cypriniformes, siluriformes and perciformes, respectively. The study led to generation of new records on GS of 43 fish species and revalidated records for 8 species. The finding is valuable resource for further research in the areas of fish genomics, molecular ecology and evolutionary conservation genetics.

Heat and chemical treatments in adult Cyprinus carpio (Pisces cypriniformes) rapidly produce sterile gonads.

Several options have been proposed for eradication of germ cells (GCs) in mammals such as treatment with cytotoxic drugs, irradiation, cold ischemia and hyperthermic treatment. Some of these methods have been also tried in fish but conditions for complete sterilisation of gonads have not been established. Here, we report the production of sterile adult common carp Cyprinus carpio in 10 weeks by the heat and chemical treatments. The cytotoxic drug busulfan (40mg/kg) was intraperitoneally injected into the animals at 2-week intervals (5 doses in total), and they were maintained in water at 38°C between Weeks 1 and 10. The effectiveness of the treatments was assessed using gonadal index, histology, and vasa gene expression. At the end of Week 10, very severe gonadal degeneration was observed in fish treated with the heat-chemical combination, and 100% of male and female fish were devoid of endogenous GCs. The average levels of vasa transcript were 0.01±0.005 and 0.02±0.016 for males and females, respectively. By contrast, high temperature alone caused minor gonadal degeneration and the gene transcript were 0.59±0.131 for male and 0.62±0.13 for female. In Week 20, after the recovery period of 10 weeks at 25°C, the gonadal germ cell did not recover from the sterile condition in any of the sampled individuals. The change in colouration of gonads was an additional useful index of the degree of gonadal sterility.