The anadromous fishes, as the salmon and shad of Europe, and the hilsa fish, the Clupea palasah of India, migrate from the sea to the fresh waters to deposit their eggs in suitable localities.
The migratory hill fishes comprise various species of large barbels (Barbus), termed Inaba seer or big-heads of India. In the Himalaya they ascend the main rivers, but turn into the side streams to breed. On the less elevated Neil glierry mountains, theydeposit their ova in the main streams, because such are small. Occasionally the fish are too large to ascend these mountain rivers, and such breed at the base of the hills, but they ascend to other feeding grounds when the rivers are in flood, and after spawning, as the water of the river diminishes, they keep dropping gently down stream. They are thus separated from and are prevented eating the young fish. In the follow ing season the fry descend to the larger rivers.
Many of the carps of the plains are migratory, and make great efforts to reach the heads of the rivers, leaping weirs and other obstructions raised to catch them. . • The Ophiocephalidme of India are known as walking or the snake-headed fishes. They and other amphibious types are monogamous. Some of them reside in ponds ; others prefer rivers, where they take up their residence in deserted holes which crabs have excavated in the banks. The pond species delight in lying at the grassy margins, where they respire atmospheric air direct. The striped Ophiocephalus constructs a nest with its tail among the vegetation, and bites off the ends of the water-weeds. Here the ova are deposited, the male keeping guard ; but should he be killed or captured, the vacant post is filled by his partner.
The hissar, Callichthys, of S. America, is like wise monogamous, constructing a nest, which it also defends. It is migratory.
Fishes which migrate in shoals for breeding purposes, as the mackerel, herrings, and some species of carp, are all polygamous.
The salmon, the shad, and the siluroid Ariinm do not appear to feed during the period of depositing their spawn. The Clupea palasah is an anadromous shad of India. It is known to the English as the pullah and hilsa or ilisha sable fish, to the Tamil as the ulum, and to the Teling race as the palasah, while the Burmese call it nga-tha-louk. In Sind they ascend the Indus in
Fehiruary to spawn, descending in September. In the Cauvery river, when the first burst of the June monsoon fills the river, they pass up and continue to do so for the next four months. The Kistna river also fills in June, but it is a more rapid river, and the hilsa defers making the ascent until September or beginning of October, when the waters are subsiding. In the Godavery, a less rapid river, they ascend most numerously from July to September, and in the Hoogly and Irawadi they continue ascending throughout the June monsoon. The main bodies of these fish ascend the large rivers of India and Burma generally when the S.W. monsoon begins in June, but not always at the same period, dependent apparently on the rapidity of the current and other causes. That it is not solely due to the presence of rain - water flooding the rivers is evident, because those of the Indus and Irawadi are mainly caused by melting snows at this period, and likewise in the latter river these fishes push on to Upper Burma, to which country the monsoon scarcely extends, but where the inundations are due to snow floods. Shad are excellent eating up to the period when they have deposited their eggs, subsequent to which they become thin, flabby, and positively unwhole some. Fresh-water fishes do not appear to be so deleteriously affected by breeding. Dr. Day counted 1,023,645 eggs in an Indian shad, and 410,500 in a barbel (Barbus sarana), and in a walking-fish (Ophiocephalus) 4700.
The gar fish (Belone) and the flying-fish (Exocetus) have filaments springing from their eggs for the purpose of attachment to contiguous objects. Among some of the marine siluroids (Ariinm) the male carries about the larger eggs in its mouth until hatched, or it may be only removes them in that manner from one place to another. Dr. Day netted many along the sea coast of India with from 10 to 12 eggs in their months, and in one there were young fry just hatched.