DISTRIBUTION OF MARINE FISHES IN SOUTH EAST 

 ASIAN WATERS 



By J. D. F. Hardenberg 



O'rganization for Scientific Research 

 Djakarta, Indonesia 



The tropical marine fishfauna of South East Asian seas has in 

 general a range from the East coast of Africa and the Red Sea in the 

 West to far in the Pacific in the East, whereby the fishfauna as a whole 

 gets poorer in species the farther away we are from the mainland of 

 Asia. 



This fauna does not reach the West coast of tropical America. It 

 is essentially an Asian fishfauna. 



There are circumtropic genera and even a few circumtropic species, 

 but the greater part of this fauna is restricted to these waters. 



Within this area several subareas can be distinguished. 



The pattern is a very complex one, regulated by several coordinat- 

 ing and correlating or sometimes contrasting factors into which we still 

 have not sufficient insight. Often it is stated in a handbook that a 

 certain species of fish is found from India to Australia, but this does 

 not always mean that it is found everywhere in the area mentioned. 

 The occurrence may be continuous but also it may be that the species- 

 is found only in isolated patches of water of gi-eater or lesser extent. 

 As a rule we can take it that fishes as well as land animals are all adapted 

 to their specific biotope. Many species are specialised in their food, 

 they are more or less adapted to a certain salinity, to the kind of bot- 

 tom and to other circumstances unknown thus far. Penetration of light 

 may be a factor too, either directly or indirectly. In this latter case it 

 is the food which is influenced directly by light. 



Copepods sink deeper in clear water at daytime and fishes living 

 on these copepods must follow them. So it happens that Decapterus 

 species in the eastern part of the Java Sea where we have clear water, 

 are living in deeper water than in the western Java Sea where the water 

 is less clear. There the schools of Decapterus are found in the upper 

 layers, sometimes even breaking surface. I kno-\\r regions where Decap- 

 terus is living so deep that they are out of reach for the fishermen. 



Thus one has to be careful when stating that a certain species is 

 absent or at any rate rare in a given area. Whereupon depends our 

 knowledge of the occurrence of a given species? The answer is just 



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