SOME TECHNICAL PROBLEMS IN FRESHWATER 

 FISH CULTURE IN JAPAN 



HIROSHI KAWATSU' 



INTRODUCTION 



During the past 10 yr. considerable attention has 

 been paid to fish culture in various countries, espe- 

 cially in the United States and Japan. Inour country, 

 freshwater fish culture has a long history, but the 

 recent remarkable improvement of culture tech- 

 niques has brought on a great change in production 

 methods. 



PRESENT STATUS OF FRESHWATER FISH 

 PRODUCTION 



Four major species of freshwater fishes are cul- 

 tured in Japan: 1( rainbow trout, Salmo gairdneri. 

 2) common carp, Cyprinus carpio, 3) eel, Anguilla 

 japonica, and ayu. Plecoglossus altivelis . From 1959 

 to 1969, production of cultured fish for food in- 

 creased from 15,000 to 52,000 tons, for a percent 



' Freshwater Fisheries Research Laboratory. Hino-shi. 

 Tokyo. Japan. 



increase of 236. This can be compared to an increase 

 of only 26% for wild fish from inland waters in this 

 same period (Table !). 



Government statistics on fish culture in Japan 

 classify the culture methods into four categories, 

 namely, 1) standing-water pond, 2) running-water 

 pond, 3) irrigation pond, and 4) net culture in lakes. 

 Running-water ponds give the highest production 

 per unit area for all species; net culture is second. 

 Harvest from irrigation ponds is slightly higher than 

 from standing-water ponds, because the larger water 

 area of the former is more favorable to the growth of 

 fish. 



In 1968, the number of ponds utilized in various 

 types offish culture was 35,239 in number and 8,500 

 hectares in area. A total of 7,5 18 of these ponds were 

 used to produce food fish. The number offish farms 

 classified by water area are listed in Table 2. Almost 

 all the rainbow trout and ayu are cultured in 

 running-water ponds, and eel in standing-water 

 ponds. In the case of carp, both standing- and 

 running-water ponds are used. Number and area of 

 ponds per fish farm are shown in Table 3. These 



Table I. — Annual catch and crop in inland waters, 1959-69. 



Source: Bureau of Statistics ( 19691. 



17 



