How is spawning triggered naturally?
Spawning, the release of gametes (mature oocytes/eggs by the female or of sperm/milt by the male) from the gonads (ovaries or testes), is the final event in the reproductive cycle (Rottmann et al. 1991a), and is the result of complex interactions between a variety of hormones and different tissues/organs in the fish's body.
The following description is a very simplified version of major events (Rottmann et al. 1991a; Figure 1a) that occur during natural spawning. Environmental and internal factors (which differ from species to species) trigger a hormone cascade leading to egg maturation and release in females, and sperm maturation and release in males. First, a hormone called "gonadotropin-releasing hormone" (GnRH) is released from the hypothalamus portion of the brain and travels to the pituitary gland, which then releases gonadotropin hormones (especially GtH-II). The gonadotropin hormones/GtH-II travel to the ovaries and testes and stimulate them to produce steroids and prostaglandins, hormones that act directly on the gonads to cause final maturation and release of oocytes ("eggs") in females (ovulation), and the release of sperm in males (spermiation) (Rottmann et al. 1991a; Evans and Claiborne 2006). In some species of fish, a compound called dopamine naturally blocks this hormone cascade and inhibits egg and sperm production under certain conditions, for example, exposure to major stressors.
What is Ovaprlm?
Ovaprlm is a two-part drug consisting of 1) a shorter, synthetic version of GnRH and 2) domperidone. Ovaprlm is marketed ready to inject in a liquid form.
In the ornamental fish industry, Ovaprlm is used as a spawning aid to induce ovulation (release of mature oocytes/eggs) and spermiation (release of milt/sperm) in mature, properly conditioned brood-fish. Ovaprlm is especially useful for species for which natural spawning in captivity is difficult to induce.
Where do I inject the fish?
First, immobilize the fish using the correct dose of an anesthetic (e.g., tricaine methanesulfonate ["MS-222"] or metomidate). Fish should be injected either in the muscle (IM) or in the body cavity (IP or ICe; i.e., in the "peritoneal cavity" or coelomic cavity) (see figures 2 and 3 ). If you are injecting into the muscle (IM), a good area in many species is the dorsal (top) area of the fish, immediately behind or near the dorsal fin. If you are following a two-injection protocol, site the two injections on opposite sides of the fish. If you are injecting the fish into the body cavity (IP or ICe), turn it so that its ventral surface (belly) is up and its posterior (back ) end is slightly elevated. Inject into the body cavity in an area that is forward of but slightly off center to the anus or vent, and be sure not to go too deep. If you make the injection too deep, you may accidentally inject into internal organs rather than into the body cavity itself.
How should I store Ovaprlm?
Store below 77°F (25°C) and protect from sunlight and sources of heat.
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