• R Natarajan

      Articles written in Proceedings – Animal Sciences

    • Laboratory reared larval stages of the marine hermit crabClihanarius clibanarms (Herbst) (Decapoda: Anomura)

      S Ajmal Khan S Sundaramoorthy Mercy Thomas T Kannupandi R Natarajan

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      The development of the larvae of the marine hermit crabClihanarius clibanarius (Herbst) reared in the laboratory (salinity 34‰±1‰ and temperature 28°C ±1°C) is reported. Four zoeal stages and a glaucothoe were observed during development. Characteristics of the larval stages are described and compared with other known species of this genus. The time taken for development from hatching to glaucothoe is given.

    • Shell selection in the estuarine hermit crabClibanarius longitarsus (De Haan)

      S Ajmal Khan R Natarajan

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      In the laboratory, under choice situation,C. longitarsus preferred shells with greater shell width and shell weight. The correlation coefficient values calculated between the crab and shell parameters in the laboratory sample showed that this hermit crab selects a shell of suitable dimension for its occupation. In the multiple regression equations calculated with carapace length against the three shell variables aperture width, shell width and shell weight which are deemed to be important for hermit crabs, the regression coefficient of the variables varied much. The unsealed first principal component explained 84·9% of the total variability of the shell parameters and scaled first principal component explained 95·8% of shell parameters. The scaled first principal component was found to be a reliable estimator of shell size and the hermit crab, if given a choice, selected a shell of suitable dimension which fits its body quite closely.

    • Fin rot and other diseases in marine fishes

      P Lakshmanaperumalsamy D Chandramohan R Natarajan

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      A survey was conducted on the incidence of diseases, by superficial appearance, in common fish species of Portonovo coast. Approximately 46,484 marine and 22,150 estuarine fishes were examined. Marine fishes alone were observed with fin rot and neoplasm while estuarine fishes were free from such abnormalities. Fin rot was recorded among seventeen species of marine fish and tumour in cat fish. Fin necrosis accompanied with haemorrhage, ulceration and loss of scales was consistent external sign of the disease. Species of cat fish, grunter, queen fish and pikes were mostly affected by fin rot at high level and the maximum peak was recorded in April. Cat fishes alone had tumour. More than 80% of the tumour bearing specimen had fin necrosis.

    • Effect of zinc on zoeal development of the estuarine hermit crabClibanarius olivaceus (Henderson)

      S Ajmalkhan K Rajendran R Natarajan

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      The 96 h LC50 value for zinc was 100 ppb. Larvae reared in 7 sublethal (1, 5, 10, 30, 50, 70, 90 ppb) and 96 h LC50 level concentrations (100 ppb) showed survival rates more than 10%, thus perfectly fitting in with definition of chronic concentration. Survival rate of larvae decreased with increase in test concentration but in the different chronic test concentrations, the overall time required for the completion of zoeal development did not differ significantly from that of control.

    • Cadmium induced vertebral deformities in an estuarine fish,Ambassis commersoni Cuvier

      V Pragatheeswaran B Loganathan R Natarajan V K Venugopalan

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      Amhassis commersoni was treated with 3 different concentrations (0·1, 0·25 and 0·5 ppm) of cadmium upto 120 days. Fishes treated in higher concentrations developed vertebral deformity and the deformation was prominent after 89th and 115th day. The levels of the vertebral minerals such as calcium, magnesium and phosphorus lowered in all exposure concentrations and minerals lost were directly proportional to the toxic concentrations. Nearly 2/3 of skeletal mineral composition was eliminated in the deformed fish. Vertebral fracture was attributed mainly to the large amount of vertebral components eliminated from the vertebrae. Vertebral cadmium accumulation was also linear in relation to the experimental concentrations.

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