Chromosomal and histological evidences of infertility in F2 and F2 backcross. Hybrid generations of Clarias anguillaris and Heterobranchus longifilis

Male meiosis was studied in 9 different mating combinations in parental, first, second and backcross generation hybrids of Clarias anguillaris and Heterobranchus longifilis. 27 bivalents were recorded in metaphase I for seven mating combinations. The number of bivalents in F1 hybrid male x C. anguillaris female could not be determined due to a high degree of clumping of the chromosomes. All metaphase I cells observed in female F1 hybrid x male H. longifilis had three complex bivalents consisting of 43.3% giant ring and 56.7% giant rod chromosomes. The number of ring bivalents per cell was higher in parental H. longifilis than parental C. anguillaris. The number of ring bivalents per cell increased from F1 (6.7 and 8.2) to F2 backcross (13.5) hybrid generations indicating increasing chromosomal instability of backcross hybrids over Fl and F2 hybrids

Karyotypic studies of freshwater prawn Machrobrachium rosenbergii

Chromosomal studies were conducted on Macrobrachium rosenbergii. On the basis of 50 metaphase plate counts, 38 metacentric, 14 sub metacentric and 66 telocentric chromosomes (2n = 118) were observed. The total length of the granomme was recorded to be 34.2 micron.