• J Rajasekharan Nair

      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.

    • Effect of teleostean prey size and salinity on satiation amount, satiation time and daily ration in the glassy perchletChanda (=Ambassis) thomassi (Day) (Pisces: Centropomidae)

      J Rajasekharan Nair N Balakrishnan Nair

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      Results of the experiments conducted to. estimate the maximum single food intake, satiation time and daily ration in the predator,Chanda thomassi using different size groups of teleostean prey (guppies) and in six non-lethal salinities are presented. The results suggest that satiation amount and satiation time vary considerably with the size of the fish prey. It is seen that the appetite of the fish is lost on consuming relatively fewer number of larger fish prey, while the predator could accommodate a much larger number of smaller prey fish of greater gross size. Also the satiation amount decreases when the prey is available in bulk than when given at regular intervals. The computed daily ration of the predator shows high values when compared with available data on other tropical predators. The over all results project the destructive potential of this predatory species coupled with its shoaling habits.

    • 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.

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