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The Fertility of Brown Trout Eggs at the Jonkershoek Inland Fish Hatchery
Author(s) -
Hey D.
Publication year - 1949
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1947)77[65:tfobte]2.0.co;2
Subject(s) - milt , hatchery , salmo , fishery , brown trout , biology , hatching , zoology , broodstock , fertility , trout , fish <actinopterygii> , aquaculture , population , demography , sociology
This paper covers the findings of 10 years of research on the problem of the low fertility of brown trout eggs (Salmo trutta) at the Jonkershoek Inland Fish Hatchery, Stellenbosch. As a background to the problem a brief résumé is given of the acclimatization of trout in South Africa with which the development of the Jonkershoek Hatchery has been closely associated. The investigation was commenced on the artificial factors such as stripping, hatching‐house technique and diet. Thereafter both the male and female stock fish were thoroughly examined and finally as complete a record as possible was obtained of climatic conditions at Jonkershoek as compared with other trout waters. The more important findings of this investigation follow. 1. The fertility of the ova was raised by a modification in stripping technique. 2. There is a period of optimum fertility at which stage the eggs should be stripped. Eggs stripped prior to this period may be infertile due to underripeness, whereas those stripped after may be overripe. 3. The maximum mortality in any one hatch of eggs can be expected on the ninth day after impregnation. 4. The genital system of the male is normal and the effective life of the milt in water does not exceed 40 seconds. 5. The genital system of the female appears to be normal. 6. By improving the diet and by regular feeding the stock fish have gained in condition, the yield of ova has been raised and the eggs made easier to strip. Good feeding of the cocks is as important as that of the hens. 7. While ecological factors such as streamflow and temperature are by no means optimum, none of the factors investigated presents a definite obstacle to the culture of trout. Although an improvement in the fertility of the eggs and general condition of the breeders has been brought about, the problem of the low fertility of the brown trout ova at this hatchery has by no means been solved. While the mean is just over 80 percent, the fertilities of individual batches vary. Not infrequently fertilities of 98 percent have been recorded, which leads one to hope that it will become possible to raise the general standard to this level.