Volume 35, Issue 2
February 1952, pages 43-109
pp 43-68 February 1952
It is observed that there are two peaks of increase in fat content. One is in the months of October-November when the catches comprise mostly 16 to 20 cm. size group, and another is in March-April when the group comprises of sizes 20cm. and above.
The major fatty condition is attributable to the feeding activity of all sizes of fish. The minor fatty condition during March-April is due to the intensive feeding of the adult group of fish.
Any fish caught in October-November (mostly 16·1 to 20·0cm. and the samll proportion of 20·1cm. and above size) is quite fatty and this fat condition must be taken into consideration in its proper utilisation for salting, freezing, canning, fishmeal preparation, etc. The fish that are fatty during March-May are above 20·1 cm. and are almost mature. The fish are fatty before spawning and lean after spawning.
The fat in immature ones (160·cm. and less) never rises above 3% in flesh whereas in the mature ones it is as high as 8·5%. The corresponding figures for the whole fish are 2·32% and 12·5%.
The variations in fat content of individuals according to sexes and gonads, and at different times of the year are also indicated.
pp 69-77 February 1952
The head, maxillo-sternal framework and endophragmal system ofNichollsia kashiense Chopra and Tiwari, are described and compared with those of other Isopods, especiallyLigia oceanica Linn.
The supra-antennal line is well developed and produced on each side into a triangular projection. Clypeus is assymmetrical and distinct from the frontal lamina. The occipital groove is incomplete and genal fossa is wanting. The presence of an incomplete maxillary sternite is an interesting feature of the maxillary somite. The tergal alæ are very vestigeal and the alar process and infero-lateral pterygoid process are wanting in the sternal alæ.
pp 78-92 February 1952
In the present investigation extending over a period of two years from June 1945 to June 1947, the stomach contents of 2,188 young fishes belonging to 21 species were examined for determining their food and feeding habits.
The young forms of almost all the species are surface plankton feeders, and are carnivorous, exceptScatophagus argus which feeds mainly on algæ.
Planktonic prawn larvae mostly belonging to the genusAcetes formed the main food of the young forms of a number of species mentioned above, whereas the grown-up ones seem to prefer mostly fish diet consisting ofBregmaceros macclellandi, Engraulis commersonianus, Otolithus argentens, Clupeids, etc.
Equula insidiatrix andE. ruconius seem to have a special liking for polychætes, whereas copepods formed the main food of the young forms ofE. fasciata during the first stage.
Diatoms in fairly high percentages were taken byMugil troschelli andM. parsia, though copepods formed their main item of food.
Amongst the Percidæ, the amphipods formed an important item of food in addition to prawn larvæ and copepods.Ambassis commersoni, however, has a greater preference to polychæte food.
The younger forms of all the Sciænids take prawns as their main food, and the percentage of their fish food goes on slowly increasing as they grow in size.
pp 93-109 February 1952
Laboratory and field experiments, carried out during 1945—48 on the acclimatisation of fry and early fingerlings of mullets (Mugil cephalus,M. sehelii, etc.),Megalops cyprinoides andElops saurus (leptocephalus and later stages),Gerres filamentosus, Scatophagus argus, Sillago. sihama,Hemirhampus gaimardi andAmbassis sp. are described.
An attempt has been made to elucidate the physico-chemical variables in the medium during the several stages of transition of the young fish from salt water to freshwater.
In the early post-larval stage, most of the above fishes possess the capacity for quick adaptation to wide and sudden fluctuations in salinity and other environmental conditions; but advanced stages (2 to 3 inches long) of atleastMegalops andElops are found to be more susceptible to such changes, resulting in considerable mortality.
The knowledge that these common food fishes, at this early stage, can withstand even direct transfer from brackish water to freshwater has a bearing on the possibilities of their successful culture in freshwater. Their small size and low mortality during acclimatisation would enable transport of large numbers at relatively low cost.