Effects of temperature and food availability on growth and RNA/DNA ratios of walleye pollock Theragra chalcogramma (Pallas) eggs and larvae

Abstract

Walleye pollock Theragra chalcogramma (Pallas) eggs were reared to first feeding stage in the laboratory at temperatures of 3°, 6°, 9°, and 12 °C. Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) content during embryogenesis were compared to temperature and embryo age. Hatching time, larval size, yolk-sac volume, and RNA content at hatching were inversely related to incubation temperature. DNA content and RNA/DNA ratios of larvae were similar on the day of hatching at all experimental temperatures. The energetic reserves available during embryonic and prolarval development are enhanced by lower incubation temperatures. Prolarvae reared at 12 °Chad high rates of yolk utilization and initial growth, but experienced reduced growth and a decline in DNA content prior to feeding initiation. The effects of food availability on nucleic acid content and RNA/DNA ratios of first-feeding walleye pollock were determined. Mean RNA and DNA content and RNA/DNA ratio of fed larvae were significantly higher than those of unfed larvae after 2 days. Starvation of larvae that had successfully initiated feeding resulted in a rapid decline of RNA content (and RNA/DNA ratio) accompanied by a slower decline in DNA.