Spawning fish hormone

Ovaprim is a widely used synthetic hormone product in aquaculture for induced spawning of fish. It’s particularly valuable for breeding species that do not spawn reliably in captivity.

Here’s a detailed breakdown of what Ovaprim is, how it works, and why it’s so important.

What is Ovaprim?

Ovaprim is a brand name for a medication containing a synthetic analog of Gonadotropin-Releasing Hormone (GnRH) combined with a dopamine antagonist.

Its two key components are:

1.Synthetic GnRH Analog ([D-Arg⁶, Pro⁹-NEt]-GnRH):

This is a man-made version of the natural fish brain hormone (GnRH) that is much more potent and longer-lasting. Natural GnRH is broken down quickly in the body, but this analog is resistant to degradation.

2.Dopamine Antagonist (Domperidone):

This is the clever part. In many fish, the neurotransmitter dopamine acts as a natural “brake” on the reproductive system. It inhibits the pituitary gland from responding to GnRH.

Domperidone blocks this dopamine brake, allowing the synthetic GnRH analog to work much more effectively.

 

How Does Ovaprim Work? (The Mechanism)

Ovaprim jump-starts the fish’s own natural reproductive hormone cascade:

1.Injection: The farmer injects Ovaprim into the muscle or body cavity of a “ripe” broodfish (a female full of eggs or a male full of milk/sperm).

2.Blocking the Brake: The Domperidone in the injection first blocks dopamine receptors in the pituitary gland, effectively releasing the natural brake on reproduction.

3.Stimulating the Pituitary:The synthetic GnRH analog then stimulates the fish’s pituitary gland freely.

4.Natural Cascade:The pituitary gland releases the fish’s own stores of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).

5.Spawning Trigger:These gonadotropins travel to the gonads (ovaries or testes), triggering the final maturation and ovulation of eggs in females and spermiation in males.

In short: Ovaprim doesn’t directly cause spawning; it tricks the fish’s body into doing it itself by mimicking the brain’s natural “go” signal and removing the “stop” signal.

 

Why is Ovaprim So Important in Aquaculture?

Induces Spawning in “Refractory” Fish:Many valuable farmed fish (e.g., carp, catfish, murrel, certain perch) will develop eggs and sperm in captivity but fail to spawn due to stress or the lack of perfect environmental cues. Ovaprim reliably induces this final step.

Synchronizes Spawning:It allows farmers to control the timing of spawning. This is crucial for managing hatchery operations efficiently, ensuring eggs are collected and fertilized at the optimal time.

Broad-Spectrum Efficacy:It is effective on a very wide range of freshwater and marine fish species, making it a versatile tool for hatcheries.

Potent and Effective:The combination of the GnRH analog and the dopamine antagonist makes it more effective than using raw pituitary extracts or other hormones like hCG (Human Chorionic Gonadotropin) for many species.

 

How is Ovaprim Used? (Typical Protocol)

1.Broodstock Selection:** Farmers select healthy, ripe females (with a soft, swollen abdomen) and males (that release milt when gently pressed).

2.Priming Dose (Optional):** Sometimes a small initial dose is given to prepare the fish.

3.Resolving Dose: A calculated dose (based on the fish’s weight) is injected. Females typically receive a higher dose than males.

4.Latency Period: After injection, there is a waiting period (usually 6 to 12 hours, depending on water temperature). This is the time it takes for the hormonal cascade to cause ovulation.

5.Spawning/Egg Stripping: After the latency period:

Natural Spawning: Fish may spawn naturally in tanks if both sexes are present.

Artificial Stripping (more common):The female is anesthetized, and her eggs are gently hand-stripped into a dry bowl. Similarly, milt is collected from the male. The eggs and sperm are then mixed for fertilization.

 

Advantages Over Other Methods

1.Pituitary Extracts: Pituitary extracts are made from ground-up fish pituitaries. Their potency can vary, and there’s a risk of disease transmission. Ovaprim is a consistent, synthetic product.

2.hCG:hCG mimics LH directly but doesn’t work well on all fish species, especially those with a strong dopamine inhibitory system. Ovaprim is often more effective for these “problem” spawners.

 

Ovaprim is a powerful and reliable tool for aquaculture hatcheries. By mimicking the brain’s natural spawning command and disabling the internal brake, it allows for the controlled and predictable reproduction of many fish species that are essential for food production and conservation efforts.

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