Volume 35, Issue 4
April 1952, pages 143-180
pp 143-154 April 1952
The peak period of occurrence ofThrissocles purava (Ham.) in Bombay waters is in two seasons, namely February-April and August-October. The mature, spent and maturing fish are caught in inshore waters in these periods. The post-larval forms are also encountered in the plankton samples taken in these months. During the remaining months a few young, immature specimens are available in small numbers.
The range of diameters of immature, maturing and mature ova is from 0·08 mm. to 0·44 mm.; 0·45 mm. to 0·76 mm. and 0·92 mm. to 1·26 mm. respectively.
The mature ovaries of this species are found to contain only two groups of ova, namely mature and immature.
The spawning season, as determined by the ova diameter measurements and the structure of the mature ovary, is found to be the same as the peak period of occurrence of this species in inshore waters. Relatively high percentages of mature and spent females during this period further supports the view that the species visits the Bombay shores mainly for spawning.
The spawning period for individual fish is of a short duration and there is only one spawning a season. The minimum period required for the rematuration of the spent ovaries is about six months.
The size at first maturity is found to be about 170 mm.
pp 155-166 April 1952
Investigations in this laboratory indicated that polyploidogens are also mutagenic and that mutagens may induce polyploidy. Doubling of the chromosomes leading to viable tetraploid races is sporadic and such an induction was observed after ultra-violet irradiation.
Experiments were therefore carried out to confirm the suspicion that a doubling of the chromosome complement after ultra-violet irradiation may be as sporadic and unpredictable as induction of a specific gene mutation.
Photographs of giant colonies of the treated and the control material are presented.
The evidence recorded in this paper confirmed the suspicion that induction of tetraploidy being conditioned by a specific gene mutation and induced gene mutations being sporadic, treatment with ultra-violet rays does not always lead to the production of tetraploidy.
The existence of multiple alleles at the locus governing the nature of sculpturing of the giant colony is confirmed.
Ultra-violet irradiation has immediate as well as delayed effects and the nature of the mutation induced is unpredictable.
A theory of the mode of action of the various biologically effective physical and chemical agents on living organisms is considered.
pp 167-180 April 1952