6 MALAYAN FISHES. 
Fish are curious creatures and we have still a great deal to 
learn about their habits. Some like the Salmon and the Shad 
(Ikan térubok) live in the sea and spawn in the rivers. Such 
fish are termed anadromous and the term is also applied to fish 
which make a migration from the deep sea coastwards for the pur- 
pose of spawning. 
Others, like some Eels, live in the rivers and spawn in the sea. 
The common Eel of Europe (Anguilla vulgaris) spawns far out 
in the ocean, after which both males and females die, never return- 
ing to fresh-water a second time. Fishes which live in the rivers 
and spawn in the sea are termed catadromous, 
Some fishes do not lay eggs but bring forth their young alive. 
Examples of viviparous fishes occur in the Shark and Ray families 
and also in the BLENNIDAE, CYPRINODONTIDAE and SCORPAENIDAE. 
Instances of functional hermaphroditism occur, and some of the 
SERRANIDAE ((Sea-Perches) are invariably hermaphrodite and self- 
fertilising. 
A Sea-Bream, Chrysophrys auratus, is an example of successive 
hermaphroditism, the male and female sex-cells ripening alter- 
nately. As. an occasional variation hermaphroditism has been re- 
corded in such well known fishes as the Cod, the Mackerel and the 
Herring." 
The eggs of fishes may be divided into two kinds; the large 
(demersal ova) which are heavy and sink; and the small (pelagic 
ova) which are buoyant and float at or below the surface according 
to their density. The buovancy of the pelagic egg depends, how- 
ever, on the density of the sea and the pelagic egg becomes demersal, 
in position, in brackish water and in fresh water. 
Demersal eges may be either viscid and adhesive or smooth 
and non-adhesive. | 
Pelagic eggs are distinguished by their lightness, buoyancy, 
small size and “remarkable transparency. They are always non- 
adhesive and free and they invariably belong to Marine Fishes. 
As a general rule it may be said that fresh water fish produce 
demersal ova and marine fish pelagic ova. 
When we realise that the eggs of most Marine fishes float, it 
is obviously futile to speak of ouarding the “ spawning grounds ” 
on our coasts. It is necessary to mention this because ‘at one time 
it was thought that spawning took place on shallow banks or even 
close in shore but this is now known to be incorrect, except in the 
case of the true Herring which lays demersal eggs in comparatively 
shallow water, and a few less important species. 
Amongst our important Marine food fishes which are known 
to produce. pelagic eggs are members of the Herring, Mackerel, 
Horse-Mackerel, Sea- Perch, Mullet and Flatfish families, i in fact, all 
our basi fish. 
Camb: Nat: Hist: 1904, 
