• Sheila Susan Jacob

      Articles written in Proceedings – Animal Sciences

    • Rate of gastric digestion in the larvicidal fishesAplocheilus lineatus (Cuv. & Val.) andMacropodus cupanus (Cuv. & Val.)

      Sheila Susan Jacob N Balakrishnan Nair

      More Details Abstract Fulltext PDF

      In the larvicidal fishesAplocheilus lineatus andMacropodus cupanus investigations on the rate of gastric digestion reveal that interspecific variations are apparent; however, within the species, digestion rate is not significantly altered by fish size provided the amount of food supplied is sufficient to fill the stomach. Gastric depletion is directly related to temperature, increasing temperature elevating the rate of digestion.

    • Toxicity of certain pesticides found in the habitat to the larvivorous fishesAplocheilus lineatus (Cuv. & Val.) andMacropodus cupanus (Cuv. & Val.)

      Sheila Susan Jacob N Balakrishnan Nair N K Balasubramanian

      More Details Abstract Fulltext PDF

      Bioassay studies reveal the toxicity levels of pesticides utilised in the area to the larvivorous fishesAplocheilus lineatus andMacropodus cupanus. The resistance of both fishes decreases with increase in period of exposure to the pesticides. Comparing the major groups of synthetic organic pesticides, the chlorinated hydrocarbons, here exemplified by DDT, are more toxic to the fishes than ekalux and malathion, the organophosphates experimented with. The carbamate sevin is the least toxic. Nevertheless, all the pesticides are ‘toxic’ to ‘very toxic’ as defined by the Joint ICMO/FAO/UNESCO/WHO group of experts, having an acute lethal threshold of below 1 to 100 mg/l.M. cupanus is the more resistant of the two fishes, probably on account of its obligate air-breathing nature, and thus its tendency to absorb less toxicant across the gills. Contrasting the susceptibility of mosquito larvae and the fishes studied to the pesticides investigated, the closeness of the LC50 values obtained inA. lineatus to that recorded in certain species of mosquito larvae indicates that whileM. cupanus could be employed in conjunction with pesticides for anti-larval work,A. lineatus should not be so utilised.

    • Reproductive biology of the larvivorous fishMacropodus cupanus (Cuv. and Val.)

      Sheila Susan Jacob N Balakrishnan Nair

      More Details Abstract Fulltext PDF

      Investigations on the maturity stages, pattern of distribution of ova in the ovary, growth of the ova to maturity, minimum size at first maturity, sex ratio, growth rate of the ovary, spawning frequency, spawning season and fish-fecundity relationships of the larvivorous fishMacropodus cupanus indicate the extent to which breeding is geared to take maximum advantage of environmental and other factors which afford the greatest opportunity for survival and development of the new generation. The mode of development and growth of the ova reveal that the first maturation is normally delayed till the main period of body growth is over; further, the linear relationships derived between growth rate of the (female) gonads and fish size are a reflection of the symmetry of the gonads. Correlating data on egg size, fecundity and conditions for incubation,M. Cupanus with its high fecundity and rapid development can be said to incline towards ‘r-selection’ on the continuum between ‘k’ and ‘r-selection’. Investigations on spawning frequency and season reveal the protracted spawning season from April to September and the shorter one in January and February. The distinct monsoon spawning peak leading to an increase of its population during this season coincides with the peak incidence of mosquito larvae, indicating the larvivorous potential of the fish.

  •  

© 2021-2022 Indian Academy of Sciences, Bengaluru.