Volume 37, Issue 6
June 1953, pages 203-248
pp 203-213 June 1953
A study has been made of the adaptive responses ofChanos to variations in external salinity and temperature. In external salinities varying from 0·l% NaCl (hard tap water) to 5·3% NaCl (sea-waterplus common salt),Chanos fingeriings retain their blood serum chloride values fairly constant over a narrow range of 0·3% NaCl. In dilutions of tap water corresponding to a chloride content of 5 p.p.m. and less, the serum chloride values suggest a breakdown of the osmoregulatory mechanism.
The period of survival ofChanos fingeriings in glass-distilled water is prolonged if they have been preacclimatised to fresh-water or if sodium or calcium chloride has been added to the medium. The serum chloride values for fingeriings kept in solutions of calcium chloride (144 p.p.m. of Ca) indicate that calcium in the external medium aids the fish in the retention of blood salts.
The chloride and calcium contents of natural fresh-waters appear to be of critical significance whenChanos is transferred direct from high salinities. The heat death temperatures ofChanos fry and fingeriings (43 and 39° C. respectively) are higher than those reported for marine fishes. The heat death temperature of the fry is not significantly influenced by the salinity of the medium, the per cent, survival of the fry at any temperature being dependent only on the temperature of the water and the time of exposure.
The fry and fingeriings are able to withstand momentary exposures to 18° C. and 14° C. respectively, both in sea-water and in tap water.
pp 214-223 June 1953
The survival of the organismsMicrococcus pyogenes var.aureus,Escherichia coli, Salmonella typhosa, Salmonella schöttmuelleri andVibrio comma in sea water and in thebombil tissue has been studied. In addition the survival of these organisms in inoculated fish subsequently refrigerated, dehydrated, or held at room temperature has been studied. The effect of heat and culinary treatment on the inoculated fish has also been observed. Our results when correlated with the casual occurrence of bacteria of faecal origin on the flesh and ventriculus of the fish, together with the findings that cocci are present in large numbers on the skin and in almost pure culture in the ventriculus of the dehydrated fish (these have been reported in a previous communication, 1953), suggest the possibilities of this fish being a carrier of enteric infections. The fact thatE. coli, S. typhosa andM. pyogenes var.aureus resist culinary treatment, also indicates that infection is possible on consuming contaminated foods, even after the cooking process.
pp 224-227 June 1953
The average fat values for the flesh of mackerels and in the whole fish show that the fish is fatty during October-November and during March-April. The plankton can be considered to be quite fatty during March and November though the peak is attained during February and May. The fattiness of the fish during March-April and October-November can be attributed to its intense feeding on plankton rich in fat.
pp 228-231 June 1953
pp 232-248 June 1953
Ten flagellate species of Chrysophyceæ, four belonging toMallomonas Perty, three toSynura Ehr., and three toDinobryon Ehr. are described.
The localities from which these algae were collected and the periods of their occurrence are given. They occur in the plains usually during winter, and at high elevations during summer.
Except for one previous record ofSynura, no flagellate members of the Chrysophyceæ appear to have been recorded in India so far. Records of even non-flagellate members of the class from India are few. The present records show that members of the Chrysophyceae are not as rare in India as believed hitherto.
pp 248-248 June 1953