460 EIGHTH PACIFIC SCIENCE CONGRESS 



teresting to observe that in a stretch, often not more than a few miles 

 wide, species occur which are replaced farther out at sea by related forms. 

 Stolephonis zollingeri and heterolohus are the more neritic, whereas 

 Stolephorus co7nj7iersoni is the more open sea form. Rastrelliger neg- 

 lectus is the coastal, R. kanagurta the replacing open sea species, Scom- 

 beromorus guttatus the coastal, Sc. commersoni the more remote form. 

 To these examples may be added various other ones like Sardinella fim- 

 briata and Sardinella perforata. 



A narrow or wider shelf is developed along the whole continent of 

 Asia, but it reaches its greatest extension in the East in the so-called 

 Sunda shelf covered by the Java Sea and part of the South China Sea, 

 and in the East in the Sahul shelf covered by the Arafura Sea. Though 

 these seas are very far apart their fishfauna is the same. 



Fishes of true oceanic waters generally avoid the shelf-seas, e.g. 

 tuna, some flying fishes, some sharks, which seldom venture far over 

 the hundred fathom line, though they are not afraid of the vicinity of 

 the coast, provided that this coast is bordered by deep water. Only the 

 dwarf bonito and the dwarf tuna, Euthynniis alletteratus and Thunnus 

 tonggol respectively, come into the shelf seas regularly. 



Fishes of the coral reefs have a very restricted habitat. Many of 

 them pass their whole life on one and the same reef and mingling of 

 the total stock happens probably only by way of planktonic eggs and 

 larvae. Others like parrot-fishes and probably species of Caesio seem 

 to spawn in open water, miles away, whereafter they return to the reefs. 

 Whether this is always the same one is still an open question. 



So we can divide the South East Asian waters into the following 

 four divisions, judging from an ecological point of view: 



1. Coastal waters. 



A broader or nanower band of water along the shores, influenced 

 by steepness or configuration of the bottom, direction and strengths of 

 currents, contamination by river water, windstrength and maybe other 

 factors. 



2. Shallow seas on a shelf. 



Shelf waters coincide with the coastal waters wherever the shelf is 

 narrow. In places where the shelf seas cover a wide area, they can have 

 their own fauna. 



3. Oceanic waters. 



These waters cover the greater part of our area and may extend to 

 the shore in places where we have a clear steep rocky coast and no rivers. 



4. Coral-reef waters. 



Coral-reef waters are very limited in extent. They are above the 

 coral reefs. 



