electrophoretic variants of catalase in black rock- 

 fish, Sehastes inennis; genetic polymorphisms of 

 tetrazolium oxidase in black rockfish; genetic con- 

 trol and subunit composition of lactate dehydro- 

 genase in Psciidorashuni puna (a cyprinoid fish): 

 duplicate genetic loci and variant forms of malate 

 dehydrogenase in chum salmon. Oncorhyiu liiis 

 kt'tii. and rainbow trout. Saliiio iniinhieii. 



Evidence has importantly been provided for the 

 tetraploid condition of salmon. This means that salm- 

 on, like many higher plants, basically have four of 

 each chromosome instead of the usual two each 

 found in normal diploid organisms. Diploidy is the 

 common stale in the animal kingdom. Further ex- 

 amination of the evolutionary process of salmonids 

 remains to be done. Already though recognition of 

 the tetraploidy of salmonids should be of intrinsic 

 importance in genetic studies. Because of the tetra- 

 ploid nature of salmon, big salmon obtained by selec- 

 tion are not a good general example of what might be 

 expected by similar programs of breeding using truly 

 diploid species. Tetraploidy lends itself particularly 

 well to gigantism. 



Study of enzyme variation in species transplanted 

 and farmed in the not-so-distant future will be an 

 important means of stock identification, and of de- 

 termining whether desired or unwanted hybridiza- 

 tion has occurred in the wild between the local and 

 transplant type. This will be no small job since the 

 present most effective utilization of different genetic 

 characters of various populations is still by trans- 

 plantation of populations and species suitable for the 

 environmental conditions of the areas intended for 

 farming (Numachi. 1972a). 



Another application of enzyme variants to genetic 

 improvement of aquatic organisms may be as mark- 

 ers linked with economic characters. Economic 

 characters are usually polygenic and so are impossi- 

 ble to study by simple Mendelian genetics as are 

 distinct, qualitative, morphological characters. 



Nikko Branch of Freshwater Fisheries 

 Research I^aboratory on Lake Chuzenji 



Breed improvement is now regarded as one of the 

 main problems in the freshwater fish culture in 

 .lapan. .Some selective breeding is underway at the 

 Nikko Branch of Freshwater Fisheries Research 

 Laboratory (for preliminary work on Stilino i^aircl- 

 iwri see Kato and .Sakamoto. 1969: Kalo. !97()), 

 Extensive hybridization studies have been carried 

 out and reported in the literature (Suzuki and Kato. 



1966: Kato. 1967: Suzuki and Fukada. 1971. 1972). 

 Most likely, such programs will be stepped up as 

 breed improvement is stressed in the future. 



It is believed that no fish populated Lake Chuzenji 

 until 1873 when some local people volunteered to 

 stock the lake with such fishes as the char and carp. 

 Since that time, many species of salmonid fishes 

 have been stocked frequently in the lake. Lhe eggs of 

 Sahelinusfontinalis, the brook trout, were imported 

 in 1901 from the United States and fry released in the 

 lake. 



It is well known that distinct species and genera of 

 fishes hybridize frequently in nature. A considerable 

 number of natural hybrids has been reported, espe- 

 cially in the freshwater families — Cyprinidae and 

 Castostomidae: also, in Percidae. Centrarchidae, 

 Poeciliidae, etc: and importantly in Salmonidae. 

 Natural hybrids seem to occur much less frequently 

 in marine fishes. Information about natural crosses 

 is most useful in determining the relationship of 

 groups of fishes. 



Natural hybrids between 5. pliiviiis. the Japanese 

 char, and S. fontinalis were collected from a brook 

 flowing into Lake Chuzenji. They are estimated to 

 constitute about 12% of the population at the area of 

 the headspring. 



Growth and survival rates of artificially produced 

 hybrids between .V. plnviiis and S. fontinalis were 

 studied from 6 mo after fertilization until they were 2 

 yr old and compared to the nonhybrid parents. This 

 was to determine their relative suitabilities for pond 

 culture. Best growth was in S. fomintilis followed by 

 the hybrid, then by S. pluvins. Survival rate was 

 highest in the hybrids. All the hybrids and S. fon- 

 tinalis came to maturity during this time, but a third 

 of S. pluvius was still immature. Hybrids were fertile 

 and. in fiKt, produced a significantly larger number 

 of eggs than did the nonhybrid parents. 



With the hope of directly utilizing the information 

 obtained to increase annual trout harvests, hybridi- 

 zation experiments with 62 combinations of Sal- 

 monidae have been going on since 1965. The purpose 

 of this work was to find F, hybrids suitable for pond 

 culture and for stocking lakes or rivers. L'ntil a few 

 years ago the freshwater fishes of Japan were abun- 

 dant in nature. They were used mostly by rural peo- 

 ple as a main protein source. Due to a reduction in 

 their natural habitats, such fish are now less plenti- 

 ful. At the same time the demand for them has gone 

 up. making them a luxury food. Presumably it was 

 believed that genetic and breeding work would have 

 some bearing on this situation. It v\as further hoped 



130 



