Fishes known to produce demersal eggs on our coasts are the Gar-Pike (Todak) and the Flying-fish (Bělalang) and their eggs have viscid threads by which they become attached or entangled with foreign objects or eggs of the same species. The eggs of the Todak may be seen entangled in fishing stakes (kelong) in masses, which look rather like cobwebs.
When the breeding season arrives fishes migrate to the localities most suitable for the deposition of their eggs. At this time our principal food fish which produce pelagic eggs proceed far out to sea against the prevailing monsoonal current. This is known as the contranatant spawning migration. After spawning, the eggs are brought back by the current towards the coast. This is the denatant drift.
Though the eggs of many species of fish hatch out fry which are miniature representations of the adult fish, the eggs of others hatch out larval forms, known as Leptocephali, which bear no resemblance to their patents. These Leptocephali are transparent, attenuated creatures, often ribbon-like in shape, with very small heads. They appear to be incapable of much effort and to be specially adapted for passive drift; in fact, the Leptocephalus stage appear to be a marvellous provision of Nature to enable the young of certain fish which spawn far out at sea to reach the shallows near the coasts in a state of suspended animation. We know that the Tarpin (Megalops cyprinoides) Malay Bulan-bulan and the Giant Herring (Elops hawaiiensis) Malay Bandang, pass through a Leptocephalus stage, and as no Malay fisherman whom I have questioned, has ever seen the Parang-parang (Chirocentrus dorab) until it was a few inches long, it may be because this fish passes through a larval metamorphosis also. It is only within recent years, that certain Leptocephali, long known to naturalists, have been identified as larval Eels.[1]
For example, Leptocephalus brevirostris is now known to be the larva of the common Eel of Europe (Anguilla vulgaris) and Leptocephalus morrisii has been watched through its metamorphosis into the Conger Eel (Conger vulgaris).
If the contranatant spawning migration is against the S. W. monsoonal current, the ova and larvae will drift in a N. E. direction and those that enter the Straits of Malacca, for instance, would gradually approach the West coast of the Peninsula. Similarly, a spawning migration in the South China Sea during the N. E. monsoon would result in the larvae being carried along and dispersed along the East coast of the Peninsula.
As the larvae approach the coast they come within the influence of the tides and while continuing their progress with the monsoon current they are carried backwards and forwards by the daily ebb and flow of the tides.
- ↑ Meek, Migrations of Fish.
