• N K Balasubramanian

      Articles written in Proceedings – Animal Sciences

    • Effect of salinity on the survival and growth ofChanda (=Ambassis) gymnocephalus (Lac.) fry (Pisces; Centropomidae)

      J Rajasekharan Nair N K Balasubramanian N Balakrishnan Nair

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      The survival and growth ofChanda (= Ambassis) gymnocephalus (Lac.) fry (8·8 ± 0·2mm) collected from Murukumpuzha Lake (9·34‰) for a ninety day period in different salinity grades were studied. A faster rate of growth is exhibited by the fish in the highest salinity grades (22·41 and 28·51‰), even though during the first month, growth and health was apparently better in the lower salinity grades (4·11, 10·21 and 16·31‰). Assimilation efficiency also showed a similar gross picture. Thus inC. gymnocephalus, an euryhaline species, the fry show preferred salinity gradients for optimum growth within the fluctuating salinity regime at a stable temperature (26 ± 2° C) and hence may make salinity bound emigrations with growth.

    • 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

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      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.

    • Condition and relative condition cycles in the tropical glassy perchletChanda (=Ambassis)commersonii(Cuv. and Val.) (Pisces: Centropomidae)

      J Rajasekharan Nair N Balakrishnan Nair N K Balasubramanian

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      The seasonal condition (K) and relative condition (Kn) cycles and their changes with the growth of the fishChanda commersonii (Cuv. and Val.) for 2 yrs are presented. BetterK is shown by the smaller immature and first maturity stages and larger, almost senile groups but they show aKn factor below ‘1’. The actively breeding adults show a uniform fail inK but they give comparatively highKn values (above ‘1’). These changes inK andKn with the growth of the fish are clearly reflected in their seasonal cycles also.K cycle would thus appear to follow a pattern of build up and loss of body resources, indirectly following the breeding cycle while theKn cycle follow the breeding and feeding cycles directly, as shown by their seasonal changes and changes with growth of the fish for 2 yrs. Since only minor deviations from unity occur inKn factor it furnishes a more sensitive index of somatic difference between age groups, of breeding season and feeding cycle.

    • Ecology of Indian estuaries—V: Primary productivity of the Ashtamudi estuary, south-west coast of India

      N Balakrishnan Nair P K Abdul Azis K Dharmaraj M Arunachalam K Krishna Kumar N K Balasubramanian

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      Primary productivity at four representative stations in the Ashtamudi estuary has been presented. The average gross and net productivities in the surface water was maximum at Neendakara, the bar mouth zone and minimum at Kadapuzha, the riverine zone consistently exposed to pollution from paper mill effluents. Ashtamudi, the station directly on the gradient line and Kanjirakode, the station equidistant from Kadapuzha and Ashtamudi presented a transition phase with regard to the primary productivity. In the bottom water also productivity was minimum at the polluted zone. Generally productivity at sub-surface levels was higher than that at the surface. A seasonal pattern, independent of various environmental parameters, was discernible both in the gross and net productivity changes at surface and sub-surface levels. High concentrations of dissolved oxygen, silicate and nitrite helped to maintain higher productivities at Neendakara, Ashtamudi and Kanjirakode on several occasions during the year. The fact that productivity at the polluted Kadapuzha station was the lowest, indicates that the paper mill effluent has considerably disturbed the productivity mechanism of this otherwise healthy ecosystem.

    • Fecundity of the allochthonous feeder,Rasbora daniconius (Ham.) and of the autochthonous feeder,Puntius amphibius (Val.)

      K Prem Kumar P A John N K Balasubramanian

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      The fecundity of an allochthonous feeder,Rasbora daniconius and an autochthonous feeder,Puntius amphibius in a perennial tropical pond was assessed and found to be higher in the latter. The fecundity of each of the species was correlated with parameters like standard length, weight offish, length and weight of ovary. A comparison of the regression coefficients in the relations statistically confirmed that as the length or weight of the fish and the length of the ovary increased the rate of increase in the number of eggs was greater inP. Amphibius suggesting a better assimilation of the autochthonous food byP. amphibius than of the allochthonous food byR. daniconius.

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