Volume regulation in eggs, larvae and adults of a brackish-water polychaete, Diopatra variabilis (Southern)

Altendant upon the stresses of an anisotonic and luctuating environment, a brackish-water organism acquires many adaptations that contribute to its successful colonisation. In the brackish-water zones of Adyar, Madras, Diopatra variabilis (Southern), a polychaete, occurs in large numbers along with Marphysa gravelyi Southern

Studies on the osmotic properties of the eggs and larvae of a brackish-water Polychaete, Marphysa gravelyi Southern

North of the Zoology Laboratory (Madras University) where the present investigations were carried on is the River Cooum. Except in the monsoons the river does not flow into the sea because of the formation of a sand bar at its mouth. By virtue of the formation of the sand bar at the mouth, about 100 yards up the river, the bed of the river is sandy and beyond it, it becomes gradually soft and clayey. The salinity of the waters at the mouth is almost that of seawater and decreases as one travels up the river into the interior

Salinity tolerance and volume regulation in four species of polychaetes

The present investigation was undertaken to understand the role of osmotic regulation in the distribution of four species of polychaetes, viz., Glycera embranchiata, Onuphis emnita, Loimia medusa and Clymene insecta in the brackish-water zones of Adyar, Madras. O. erimita .lIong with G. embranchiala are restricted to the shore and do not occur in the brackish-water zones: L. medusa occurs in the brackish-water zone but confined only to regions of higher salinity equal to the salinity of sea-wate

Gross morphology and histology of nephridia in four species of polychaetes

In a recent paper (Krishnamoorthi, 1962) it was shown that the four polychaetes studied, viz., Glycera embranchiata Ranganathan, Onuplzis ertmita , Loimia medusa Savigny and Clymene insecta Ehlers, exhibited differences in their capacities for volume regulation when subjected to stresses of anisotonic media. Jurgens ( 1935). Beadle (1937) and Ewer and Ewer (1943) have brought evidence of the relative importance of excretory organs in the volume regulation of the polychaetes they had studie

Cat fish; General remarks and future approach

Consequent upon the recent introduction of mechanised fishing on a large scale with trawls as the chief gear all along the Indian coast, many hitherto less known demersal fisheries have come to occupy a prime place on the fisheries map of India. One such group is the catfish assemblage. With an estimated annual average catch of 52 thousand tonnes over a five year period from 1977 to 1982, the catfishes constituted about 4% of the total estimated 'all-fish' catches. Though the increase in the catfish landings was nominal during the 8-year period from 1962 to 1969, a three fold increase was noticed during the succeeding period up to and inclusive of 1984. This increasing trend is reflected in the estimated landings in most of the maritime states of India

Fishery resources of the Rrameswaram Island

The Rameswaram Island, a comparatively small, 64 sq. mile area lying 3 miles off the coast of Mandapam in the Ramnad District is one of the important fishing centres of South India, fishermen forming the major portion of its population and fishing the main occupation. Surprisingly, however, factors hke the fishing conditions in the Island, the fishery wealth of the area or even the order of magnitude of the annual catch hitherto remained largely unknown. Obviously, a detailed survey, lasting for a few years, was necessary to study the fishery resources of the Island. The work was taken up early in 1952 at the suggestion of Dr. N. K. Panikkar. Since no information of any kind was available to start with, a preliminary survey was found essential to help planning the design of the actual survey. The results of the preliminary survey are first put down in the next section. Then the design of the actual survey has been briefly described. The rest of the paper contains the results derived from the data collected during the 2 years' survey from July 1952 to June 1954

Observations on the spawning season and the fisheries of the spotted seer Scomberomorus guttatus (Bloch & Schneider)

The spotted seer or Scomberomorus guttatus, is an important and much esteemed table fish, standing next in importance to Leiognathus splendens in the fishery of Rameswaram Island, where approximately 320 tons of this fish, fetching a market price of about Rs. 250,000, are landed every year (Krishnamoorthi, 1958). It is well known in the fishery of all coastal areas of India. Nevertheless the available literature furnishes Uttle exact information about its biology except for some remarks on taxonomy and geographical distribution by Day (1889) and Weber and Beaufort (1951), a description of the egg by Delsman (1931) and notes on life-history and feeding habits by Vijayaraghavan (1955). Accordingly, the present study was initiated to gather some knowledge of the biology of this important commercial species

Estimated resources of demersal fisheries off North Tamil Nadu- South Andhra Coasts Based on exploratory surveys

The results of analyses of exploratory trawling survey data for areas north of latitude zone 1O' 4O'N (off Velanganni) up to '15' 40' (off Nizampatnam) for a nine year period from 1973 to 1981 are presented. In the entire region explored, a potential yield of 1.09 t km could be expected. Barring the latitude zone 10' 40', the lowest yield (0.7 t km-') was observed off Madras/Ennore zone (13°10'). With this zone as a reference point, the following conclusions could be drawn: a) increasing trends in both southern and northern zones and b) the northern zones were comparatively richer in yields

Activity of Marphysa gravelyi Southern (Polychaeta) under heterosmotic conditions

Marphysa gravely; Southern is a common polychaete which occurs in the muddy substratum of the brackish-water regions of Madras, where salinities fluctuate over a wide range (Panikkar and Aiyar, 1937). In the laboratory under experimental conditions the worm is able to tolerate dilutions of sea-water ranging from 20-70% without any ill effect

Age and growth of Metapenaeus monoceros (Fabricius) along the Kakinada coast

Age and growih of Metapenaeus monoceros have been estimated separately for males and females by length-frequency analysis in view of the differential growth observed in the species. Modes traceable for three months were considered for the application of Food-Walford plot to estimate growth parameters. Lα for males and females is estimated as 178.4 mm and 207.3 mm respectively. The K values are estimated as 1.68 for males and 1.62 for females. Values of to obtained by the method of Gulland are 0.048 years and 0.066 years for males and females respectively