The effect of whole body lipid on early sexual maturation of 1 q age male chinook salmon ž / Oncorhynchus tshawytscha

Ž Early sexual maturation of male chinook salmon maturation 1 to 4 years prior to females in . the same age class results in reduced effectiveness of stock enhancement programs and a financial loss to the salmon farming industry. Previous studies in Atlantic salmon have shown that the age of maturity in males is affected by growth andror body energy stores, but the relative roles of these two factors are not well understood. Therefore, an experiment was designed to determine when spermatogenesis was initiated, to characterize the endocrine changes during the onset of puberty in male salmon, and to determine if the level of whole-body lipid affects the Ž . incidence of early male maturation in a wild stock Yakima River of 1q spring chinook salmon. Fry were fed a commercial diet from February until August and were then divided into groups of Ž . Ž . 320 fish mean weight, 5.6 g and fed one of five experimental diets two replicate groupsrdiet containing 4%, 9%, 14%, 18% or 22% lipid and 82%, 77%, 73%, 69%, or 65% protein for 13 Ž . months. Fish were reared on natural photoperiod and ambient temperature 68C to 168C , and pair-fed to a level based on the tank with the lowest feed consumption. Fish were weighed Ž . monthly and sampled to determine body composition, pituitary follicle-stimulating hormone FSH Ž . Ž . and luteinizing hormone LH levels, plasma insulin-like growth factor I IGF-I levels, and stage of gonadal development. Throughout the experimental period the mean fish weight was similar among treatment groups. However, from December through the end of the experiment in the following September, maturing males were significantly larger than nonmaturing fish. Initial lipid levels in 0-age experimental fish were near 6%, which is similar to wild fish of the same stock and age captured in the Yakima ) Corresponding author. Tel.: q1-206-860-3393; fax: q1-206-860-3467. Ž . E-mail address: karl.d.shearer@noaa.gov K.D. Shearer . 0044-8486r00r$ see front matter q2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 00 00406-3 ( ) K.D. Shearer, P. SwansonrAquaculture 19

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