Protein and Lipid Content of Gonads, Liver, and Muscle of Northern Pike (Esox lucius) in Relation to Gonad Growth

Northern pike (Esox lucius) were sampled at regular intervals from Lac Ste. Anne, Alberta, between May 1973 and July 1974. Gonad weight, liver weight, somatic body weight, and the total protein and total lipid content of gonads and liver were determined for a pike of 50 cm fork length to evaluate the deposition of nutrients into gonads and to assess areas of possible nutrient storage and depletion. Protein, lipid, and water concentrations in muscle, gonad, and liver were also measured. Gonad growth began in July and proceeded at a similar rate between sexes during late summer. Testicular growth was complete in September, whereas ovarian growth continued through fall and winter until April. Mature ovaries contained 14.5 times more protein and 10.5 times more lipid than did mature testes. Ovarian growth before March occurred without any depletion of body nutrients. Liver weight in both sexes increased 2.5-fold between May (after spawning) and March. In March, total liver protein of females was 163% that of males. Female liver size decreased significantly before spawning (March–April) coincident with final gonad growth. Male liver size decreased significantly over spawning (April–June). No fat storage depots were observed in either sex. Muscle and somatic body weight data indicate that a depletion of body energy can occur in spring. Key words: protein, lipid, water, gonad, liver, muscle, northern pike, Esox lucius, spawning