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Studies were undertaken to identify genetic relationship and diversity of Clarias batrachus L. populations collected from hatchery and wild stocks through random amplified polymorphic DNA (RAPD). 16 decamer primers were used for screening, out of which five produced amplicons. A total of 1376 RAPD bands ranging from 0.2 to 1.36 kb were amplified using five selected primers. The number of amplification products produced by a primer ranged from as low as three to a maximum of 18, with an average of 16 bands per primer. 8.1 to 13.71 polymorphic bands per primer were amplified. The polymorphic bands in these populations ranged from 56.4 to 59.6%. Polymorphic bands per lane within populations ranged from 4.88 to 5.3%. The similarity within the population from wild varied from 0.40 to 0.83 with a mean ± SE of 0.57 ± 0.08. The Jaccard's similarity coefficient ranged from 0 to 0.27. At 0.06 similarity coefficient, two major clusters were formed, which indicates that the genotypes belonging to same clusters were genetically similar and those belonging to different clusters were dissimilar. Significant (P < 0.05) population differentiation indicated some degree of intra-and inters-population genetic variations in two populations of catfish. This might be due to difference in habitat and breeding strategies between the two populations.

An experiment was conducted to study the effect of heavy metals (Cd, Cr and Pb), soil texture (sandy, loam and clay) and incubation periods (7, 15, 30, 60, 90 and 120 days) on soil respiration (CO 2 evolution) during sugarcane trash decomposition in laboratory conditions of the Indian Institute of Sugarcane Research, Lucknow, India. Surface soils (0-15 cm) were collected from agricultural fields and crop residue of sugarcane trash (Saccharum officinarum L.) was taken in the institute farm. Crop residue (10 t/ha) and heavy metals (10, 50, 100, 1000 µg/g) were mixed and incubated at 30°C ± 2°C in an incubator. The rate of soil respiration (CO 2 evolution) decreased with increasing heavy metals concentration. During the 120 days, the toxicity decreased but still remained significant. Maximum soil respiration was recorded at 7 days of incubation period; further, it decreased with increasing incubation period. The highest drop of soil respiration rate was caused by addition of 1000 µg/g Cd, Cr and Pb levels. Clay soils evolved maximum CO 2 followed by loam and sandy soil.

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