• N Balakrishnan Nair

      Articles written in Proceedings – Animal Sciences

    • Maturation and spawning in the hill-stream loachNoemacheilus triangularis Day

      S D Rita Kumari N Balakrishnan Nair

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      Five stages of maturity have been delineated forNoemacheilus triangularis Day. Progression of the mode in each stage of maturity has been traced from ova|diameter studies. The size at first maturity for male is around 44·5 mm and for female around 52 mm. Spawning is asynchronous and prolonged. There may be successive spawning during the year. Sexes are present in almost equal numbers. Fecundity is dependent on length and weight of fish and on length and weight of ovary.

    • Oogenesis in a tropical loachLepidocephalus thermalis (Cuv. & Val.)

      S D Rita Kumari N Balakrishnan Nair

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      The development of oocytes has been traced in detail in the loachLepidocephalus thermalis. The various stages of oocytes are described under distinctive stages namely 1. chromatin nucleolus stage; 2. perinucleolus stage; 3. yolk vesicle stage; 4. primary yolk stage; 5. secondary yolk stage; 6. tertiary yolk stage; 7. migratory nucleus stage; 8. pre-ripening stage; 9. ripe egg stage. The yolk deposition is initiated as minute globules in the extravesicular ooplasm. A yolk nuclous is entirely wanting in any stage of oocyte maturation. The origin of new crops of oocytes and the formation of the micropyle are described. Nature of degeneration of unextruded ripe oocytes has been followed.

    • Morphology of the copepodid stage of three marine lernaeopodids (Crustacea: Copepoda) from the South-West Coast of India

      A Chandran N Balakrishnan Nair

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      Full illustrated descriptions are presented of the copepodid stage ofPseudocharopinus narcinae (Pillai),Isobranchia appendiculata Heegaard andBrachiella trichiuri Gnanamuthu. The structure of the copepodid ofP. narcinae is similar to that ofP. dentatus (Wilson). The copepodids of bothI. appendiculata andB. trichiuri are identical with regard to the structure of the second antenna, first maxilla and second maxilla. This structural similarity of the copepodids ofI. appendiculata andB. trichiuri indicate the phylogenetic position of theBrachiella andClavella groups within the family Lernaeopodidae.

    • Morphology of the male ofPseudocharopinus narcinae (Pillai) (Copepoda : Lernaeopodidae)

      A Chandran N Balakrishnan Nair

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      The male ofPseudocharopinus narcinae (Pillai) is described and illustrated for the first time. All the other known males of the genusCharopinus Kroyer,Pseudocharopinus Kabata,Schistobrachia Kabata,Dendrapta Kabata andCharopinopsis Yamaguti are compared with that ofPseudocharopinus narcinae.

    • Nature of infestation of fishes byLemanthropus gibbosus Pillai andL. koenigii Stp. and Lutk. (Copepoda : Anthosomatidae) along the South-west (Trivandrum) coast of India

      S Radhakrishnan N Balakrishnan Nair

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      The nature of distribution, mode of attachment, incidence and intensity of infestation and the nature of damage by two host specific anthosomatid copepod parasites,Lemanthropus gibbosus Pillai andL. koenigii Stp. and Lutk. infesting fishesSaurida tumbil (Bloch) andParastromateus niger (Bloch) respectively, along the South-west coast of India are described. The results show that both these parasites are of serious concern to their hosts causing irreparable damage to the gills both by way of their mode of attachment and feeding activity. The blood circulation of the gills is severely curtailed and the infested gill filaments are completely put out of function.

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

      Sheila Susan Jacob N Balakrishnan Nair

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      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.

    • Host specificity and biochemical changes in fishes owing to the infestation of the isopod,Alitropus typus M. Edwards (Crustacea: Flabellifera: Aegidae)

      G Achuthan Nair H Suryanarayanan N Balakrishnan Nair

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      Data are presented to indicate the nature of host-specificity shown by the juveniles of the isopod,Alitropus typus M. Edwards and the biochemical changes in certain host fishes attending the infestation. Even though specific host preference is apparently lacking, the frequency of attack on different fishes varies. Thus among the 9 species of fishes tried,Anabas testudimus (Bloch) was found to be most severely attacked by these isopods whereasPuntius sarana subnasutus (Val.) was comparatively less affected. Proximate analyses on 5 different species of fish, viz.,Channa orientalis (Cuvier),Anabas testudineus (Bloch),Lebistes reticulatus (Peters);Tilapia mossambica (Peters) andMacropodus cupanus (Cuv. and Val.) suggest depletion of biochemical constituents on account of infestation. An increase in the moisture content in the infested fish from those of the non-infested ones was noticed with the increase ranging from 1·19% in the femaleT. mossambica to 10·15% in the maleL. reticulatus. A drastic fall in protein, glycogen and lipid was also observed in the infested fish tested. Among the various fishes tried, the minimum depletion of glycogen occurred inC. orientalis (1·44%) and the maximum in the femaleM. cupanus (7·16%). In the case of lipid, the maleL. reticulatus showed only marginal reduction (0·96%) whereasC. orientalis showed 13·20% depletion. Regarding protein, the maximum reduction after infestation was observed inA. testudineus (20·91%). The possible reasons for the depletion of these biochemical constituents in the infested fish are discussed in detail.

    • 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.

    • 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 factor ofAmblypharyngodon chakaiensis Babu and Nair in the Chakai boat channel (Trivandrum-Kerala-India)

      N Babu N Balakrishnan Nair

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      Condition factor (K) and relative condition factor (Kn) ofAmblypharyngodon chakaiensis Babu and Nair males and females respectively have been studied in relation to the various months of the year and length groups. No significant correlation exists between the proportion of the males in the population and value of condition factor (K). On the basis ofK andKn and the various length groups in respect of males and females are arranged into three classes and their incidence in the pre-spawning, spawning and post-spawning seasons were represented. In femalesKn showed significant positive correlation with gonadosomatic index. The size at first maturity observed by direct observation of the gonads in females and males agrees with the inflexions on the curve depictingK andKn with respect to length groups. The influence of feeding intensity onK does not seem to be quite apparent inA. chakaiensis. The steady fall inK in the males seems to be related to the decrease in the percentage occurrence of males of these length group in the sample.

    • Taxonomic value of torus longitudinalis and valvula cerebelli in four species ofAmblypharyngodon Bleeker (Pisces, Teleostei, Cyprinidae)

      N Babu N Balakrishnan Nair

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      The configuration of valvula cerebelli and torus longitudinalis shows distinct variations at the level where the tractus mesencephalocerebellaris posterior establishes full connection with the granular valvula in the four species ofAmblypharyngodon. The taxonomic value of the configurational variations of mesencephalon of the four species has been discussed.

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

      Sheila Susan Jacob N Balakrishnan Nair

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      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.

    • 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.

    • The problem of marine timber destroying organisms along the Indian coasts

      N Balakrishnan Nair

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      The serious problem of destruction of wood in sea and brackish waters of India has been discussed with special reference to the organisms that are involved, their distribution, nature of infestation and vertical distribution, seasons of settlement, duration of larval period, growth rates and dispersal. The different ecological factors that determine the distribution of borers have been described such as temperature, salinity, primary film, rate of water flow, turbidity, pollution, effects of fouling, parasites, predators and associates. Control measures to check their ravages are also indicated.

    • Ecology of biofouling onCrassostrea madrasensis (Preston) (Mollusca:Bivalvia) in a tropical backwater

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

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      Ecology of biofouling on the edible estuarine oysterCrassostrea madrasensis (Preston) has been investigated in the Ashtamudi Backwater of the southwest coast of India. Fouling was highly conspicuous throughout the year and dominant groups included barnacles, serpulids, bryozoans and modiolids. Intensity of fouling varied from 73 to 179 % on living oyster valves and 65 to 172 % on dead valves with respective annual averages of 118 and 127%. Substrate selection and settlement of the different groups were mostly opportunistic. Barnacles were the most dominant, living and dead ones collectively contributing to about 26 % of fouling on living valves and 32 % on dead valves. Serpulid fouling was 22 % both on living and dead oyster valves, bryozoans 15 and 12%, modiolids 11 and 12% and the miscellaneous groups formed 27 and 20 % respectively. Availability of free settling space and fouling in relation to substrate size were also investigated. Total fouling was very intense on oysters of 25–35 cm2 size group. Impact of biofouling on oysters and certain earlier studies on the topic are discussed.

    • Ecology of Indian estuaries: Studies on the zooplankton ecology of Kadinamkulam Backwater

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

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      Ecology of the zooplankton of Kadinamkulam Backwater, a brackish water lake along the south-west coast of India, has been studied from February 1980-January 1981. Seasonal distribution of the zooplankton followed an uniform pattern throughout the backwater. Zooplankton in the Kadinamkulam Backwater is composed of foraminifers, coelenterates, nematodes, rotifers, chaetognaths, polychaetes, cladocerans, ostracods, amphipods, copepods, decapod larvae, insect larvae, bivalves, tunicates, and fish eggs and larvae. Among these, rotifers, copepods and copepod nauplii are the major components which form the bulk of the zooplankton (nearly 98 %). A distinct regional variation is discernible in the dominance of zooplankton components. Copepods constitute the dominant group near the barmouth and middle portion of the backwater, while rotifers are dominant in the upper reaches, where freshwater influx was relatively high. Factors influencing seasonal variation and distribution have also been discussed.

    • Transpiration rates and acclimation to water and temperature of the tropical woodlice,Porcellionides pruinosus Brandt andPorcellio laevis Latreille

      G Achuthan Nair N Balakrishnan Nair

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      The transpiration rates and acclimation to water and temperature ofPorcellionides pruinosus Brandt andPorcellio laevis Latreille, the common terrestrial isopods occurring in and around Trivandrum, India, were studied. Transpiration rates in different temperatures (24 to 50°C) were higher in both the species during the first 15 minutes’ exposure when compared to 1-hour duration. Previous acclimation to different humidity and temperature conditions affected the transpiration rates in both the species and lower rates of transpiration occurred in isopods acclimated to dry conditions and higher temperatures. Survival rates improved at lethal temperatures in specimens acclimated to 34° C.

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