aquaculture system is 90%; minimum survival is 

 60%; mean survival is about 709f . Bacteria of the 

 genus Vibrio are the major cause of mortahty, but 

 infections can be controlled to a certain extent by the 

 use of nitrofuran. sulfa drugs, and terramycin. In the 

 United States, nitrofuran probably could not be used 

 for this purpose since it has not been cleared for use 

 in treating food products by the Food and Drug 

 Administration. 



A new commercial trout farming project was ob- 

 served at Karakuwa at the head of Ogatsu Bay dur- 

 ing October 1971. This project, which is operated by 

 Fishermen's Cooperative Association with the gui- 

 dance of Koganezawa, included shore-based 

 facilities for rearing trout and acclimating them to 

 seawaterand a series of net enclosures for culture of 

 the trout in the marine environment. 



Shore facilities included six circular concrete 

 tanks, 12 m in diameter and 2.5 m deep, with four 

 more to be built. The fish will be reared for approxi- 

 mately 1 yrin these tanks before they are acclimated 

 to seawater and transferred to the floating net en- 

 closures. This year, since the project was just begin- 

 ning, the fish were raised at another location and 

 were brought to Karakuwa for acclimation to salt 

 water and transfer to growing pens. A system of 

 large plastic pipes makes it possible to drain each of 

 the large round tanks to transfer the 14,000 trout 

 which will be acclimated in each tank into a long 

 drainage channel which takes them to the shore 

 where they can be transferred through pipes into the 

 floating pens. 



The floating pens are anchored in Ogatsu Bay 

 which is well protected from storms by steep hills. 

 The water in this area is 10-30 m deep and varies in 

 temperature from above 8°C during the winter to a 

 maximum temperature of 23-25°C during the sum- 

 mer. 



The fish are fed ground raw fish and meal, making 

 a product similar to Oregon moist pellets which is 

 used in U.S salmon hatcheries. This food has been 

 found to be better than dry pellets. 



Only female trout are used in this type of culture as 

 they are more disease resistant and are easier to 

 acclimate to seawater than males. Also, females can 

 mature in the sea in 2 yr producing healthy viable 

 eggs, whereas males require fresh water to become 

 mature. The sorting of male trout from female trout 

 at a size of 18 cm is a time consuming operation. 



The price of marketable trout 1.5-2.0 kg in weight 

 is 450-550 yen ($1.46 to Si. 79) per kilogram in the 

 Tokyo fish market. This is about the same price as 



yellowtail Seriola. whereas smaller rainbow trout 

 which weigh 150-200 g each sell for 250-300 yen 

 ($0.81 to $0.97) per kilogram. In comparison, salmon 

 from natural production sell for 600-800 yen ($1 .95 to 

 $2.60) per kilogram. 



One of the problems of raising rainbow trout in net 

 enclosures is that they have tender skin and may lose 

 some scales rubbing against the netting which may 

 permit the entrance of the bacteria Vibrio. Japanese 

 scientists have found that adding 10 jig of testos- 

 terone per gram of food will increase the mucous 

 production in skin which will protect the scales from 

 erosion. It is unlikely that testosterone could be used 

 in the United States for this purpose because it is 

 considered to be a carcinogen. 



Another trout, Salreliniis pliivius, known as the 

 steelhead, is being reared experimentally in seawa- 

 ter at the Miyagi Prefectural Field Station at Ogatsu 

 Bay. According to Koganezawa, S. pluvius spawns 

 in the headwaters of streams, is very resistant to 

 changes in temperature, and can be successfully ac- 

 climated to seawater. Therefore, this is considered a 

 good species for aquaculture, although it is not 

 reared commercially at the present time. 



SALMON CULTURE 



The first Japanese pilot-scale experiments in cul- 

 ture of salmon in floating net pens in the marine 

 environment are being conducted at Yamada Bay in 

 Iwate Prefecture. Yamada Bay is completely en- 

 closed except for a narrow entrance where the water 

 is reported to be 90 m deep. Hills protect the inner 

 bay from storms making it an ideal location for 

 aquaculture. The Bay is about 60 m deep in the 

 center, but 15-25 m deep in the area where the 

 salmon culture rafts were anchored. 



The objective of these experiments at Yamada 

 Bay which was visited in October 1971 is to perfect 

 methods which could be used commercially to rear 

 salmon to marketable size in the sea. 



The first experiments were with the chum or dog 

 salmon. Oncorhynchus keta. which had been 

 hatched at Fishermen's Cooperative Association 

 hatchery at Miyako Bay just north of Yamada. This 

 hatchery which is located on the Tsugaruishi River 

 has a capacity of 50 million eggs and is one of the 

 many hatcheries operated by local Fishermen's 

 Cooperative Associations. These hatcheries take 

 eggs from chum salmon in November, December, 

 and January when the fish enter the streams, or 

 occasionally from those salmon which are caught in 



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