182 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 terubok) live in the sea and spawn in the rivers. Such 

 fish arc formed anadromoiis and the term is also applied to fish 

 which make a migration from the deep sea coastwards for the pur- 



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

 Examples of viviparous fishes occur in the Shark and Kay families 

 and also in the Blkxxidae, Cyprinodontidae and Scoiu'aexiihe. 

 Instances of functional hermaphroditism occur, and some of the 

 SOERRANIDAE (Sea-Perches) are invariably hermaphrodite and self- 



A Sea-Bream. < 'hr/tsnpln-i/s 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. 1 



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 buoyancy of the pelagic egg depends, how- 

 ever, on the density of the - a and the pelagic egg becomes demersal, 



l>emer>al egg- may be either viscid and adhesive or smooth 



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 guarding the " spawning grounds " 

 on our coasts. It is necessary to mention this }>ecause 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 



Amongst our important Marine food fishes which are known 

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

 Horse-Mackerel. Sea-lVivh. Mullet and Flatfish families, in fact, all 

 our best fish. 



