6 MALAYAN FISHES. 



Pisli are curious creatures and we have still a groat deal to 

 learn about their habits. Some like the Salmon and the Shad 

 (Ikan terubok) live in the sea and spawn in the rivers. 8uch 

 fish are termed anadromous and the term Ls also applied to fish 

 \\'hich make a migration from the deep sea coastwards for the pur- 

 pose of spawning. 



Others, like some Eels, live in the rivers aaid 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. Fdshes which live in the rivers 

 and spawn in the sea are termed eatadromous. 



Some fishes do not lay eggs but bring forth their young alive. 

 Examples of viviparous fishes occur in the Shark and Eay families 

 and also in the Blexnidae, Cypeinodoxtidae and Scoepaenidae. 

 Instances of functional hermaphroditism occur, and some of the 

 Seeeanidae (iSea-Perches) are invariably hermaphrodite and self- 

 fertilising. 



A Sea-Bream, Chrijsoplirtjs 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 fl-ell known fishes as the Cod, the Mackerel and the 

 Herring.^ 



The eggs of fishes may be divided into two khids : tlie large 

 {demersal ova) which are heavy and sink; and the small {pelagic 

 ova) which are buoyant and float at or below the su.rface according 

 to tlieir density. The buoyancy 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 eggs may he either viscid and adhesive or smooth 

 and non-adhesive. 



Pelagic eggs are dist^inguished by their lightness, buoyancy, 

 small size and remarkaible transparency. They are always non- 

 adhesive and free and they invariably belong to Marine Fishes. 

 As a general rule it may be said that fre,4i water fish produce 

 demersal ova and marine fish pelagic ova. 



Wlaen we realise that the eggs of most Marine fishes float, it 

 is obviously futile to speak of guarding 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 tliis is now kno"ttai 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 kno^m 

 to produce pelagic eggs are members of the Herring, Mackerel, 

 Horse-Mjickerel, Sea-Perch, Mullet and Flatfish families, in fact, all 

 our best fish. 



iCamb: Nat: Hist: 1904. 



