Physiology of Finfish and Shellfish (2+1)

3.1.16. Outstanding differences are listed below

1. Body shape is an important secondary character. The female is pot bellied than the male particularly when she is ripe or near ripe for spawning because of ovaries.
2. Many fishes develop a “nuptial dress” which is particularly clearly expressed in the salmonids. During the reproductive period the change is first of all expressed in the colouration which becomes much brighter and in which colours appear that were not present before. Particularly in the males, the skeleton of the jaws become bent and large teeth appear on them. In the cyprinoids, the nuptial dress is expressed in the appearance of a brighter colouration and of peculiar tubercles on the horny epithelium of the head and scales of the body. Very great changes occur in the colouration of many gobies. (Fig.).
3. Both the paired and the unpaired fins are slightly larger in males than in females (Fig.).
4. In some fishes, the lower lobe of the caudal fin is greatly extended Eg. Sword tail.
5. In the males of several species, the anal fin becomes enlarged into an intromittant, copulatory organ designated as gonopodium. Eg. Gambusia affinis (Mosquito fish), guppy.
6. The pelvic fins of sharks are modified as claspers or myxopterygia.
7. Colouration also serves sexual distinction which is termed sexual dichromatism. In general, males are brighter in colour than females.
8. Head characteristics also serve to distinguish the sexes among fishes. In the chimeras, the male develops a spiny stout, retractile knob, the frontal clasper on the upper part of the head which has similar characteristics of forehead brooders.
9. Deep sea angler fish, the male is minute and is parasitic attached to a larger female (Fig).