Induced ovulation in coho salmon ( Oncorhynchus kisutch). I. Further studies on the use of salmon pituitary preparations

Abstract

The work presented extends previous studies on the use of pituitary preparations to induce ovulation in coho salmon. It has been demonstrated that coho salmon may be successfully induced to ovulate up to 2 months prior to their normal peak spawning period and that the use of a single injection of salmon pituitary extract (SPE) to induce ovulation is possible. In November 1977, the experimental fish were divided into six groups. Three groups were administered injections of 0.1 mg/kg partially purified salmon gonadotropin (SG-G100) followed 3 days later by either 2.0 mg/kg SG-G100, 25.0 SPE or 50.0 SPE. A fourth group was administered 10.0 mg/kg SPE followed 3 days later by 50.0 mg/kg. The fifth group received a single injection of 100.0 mg/kg SPE. A control group was injected with saline. All treated groups ovulated significantly earlier than the control. Egg survival and mean egg diameter were within the normal range for coho from Big Qualicum. In September and October 1978, the 10.0 mg/kg SPE primer followed by a 50.0 mg/kg secondary SPE injection were compared to a saline control. In addition, in September a second test group was administered the same primer but was followed by three daily 25.0 mg/kg SPE injections. All treatment groups ovulated significantly earlier than their controls. However, only the 10–50 SPE treatment groups reached cumulative ovulation levels comparable to the controls. Further, these levels increased with closer proximity to the normal spawning period from approximately 40.0% in September to approximately 80% in October. Egg survival and mean degree days to the eyed stage and to hatching for the October experiment fell within the normal range for the Big Qualicum stock. In November 1978, four groups of seven fish received single intraperitoneal or intramuscular injections of either 33.0 mg/kg or 66.0 mg/kg SPE. A control group was injected with saline. All groups ovulated significantly earlier than the control. No significant differences were found between test groups related to dosage level or route of injection. Egg survival and mean degree days to the eyed stage and to hatching fell within the normal range for this stock.