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Hormone Spawning of Australian freshwater fish

PERCH MAN

Hormone spawning - hormone induction spawning

Many Australian freshwater species only spawn when certain conditions occur.

These conditions are known as "environmental triggers."

Generally speaking the females begin to produce oocytes (Eggs inside the female before spawning) when the water temperatures begin to rise.

As the water temperature rises a few other things happen that help the fish prepare for spawning.

The warming water makes it possible for the fish to move faster so now the fish is a more efficient hunter of shrimp and any other small aquatic animals that are good food for a fish making oocytes.

The energy the fish must put into making these oocytes requires a better diet.

The warming water also means the insects that have an aquatic life stage are actively reproducing, as are other foods such as shrimp.

In the colder water during winter, the silver perch and jade perch feed on slightly different types of food.

When I have been collecting jade perch in the wild during winter, they excrete filamentous algae as I am releasing them from the net.

These species are grazers and will eat any vegetation that is convenient.

The aquatic insect larvae, and small shrimp have different nutritional value, and contain some nutrients at significantly higher levels that vegetation.

Below Filamentous algae that I cultivate to feed my breeders avoiding the fat build up in their body cavities.

See this webpage for detailed explanation. (Members only)

In summery, 1, water temperatures are rising and 2, the type of food available has changed.

These are two of the environmental triggers that get the spawning process started.

The final environmental trigger (Once the water temperature is at "spawning temperature.) is sustained flowing water.

The female has already produced the oocytes, and is waiting for the final environmental trigger, the flowing water.

Below is a picture of the oocytes in one of the female's ovaries.

When this happens the female produces the ovulating hormone that will trigger spawning.

Brood fish held in ponds must not be exposed to flowing water.

This could result in the fish spawning in the pond.

This has happened to me, and the result was no fry at all.

Well managed brood fish can be accessed with a sein net and selected by skilled hatchery staff, then transported to the hatchery for final inspection. Click the picture of the oocytes under a microscope for the video.

In the hatchery lab the oocytes can be examined and an ovulating hormone can be administered to induce natural spawning activity .

See this video of jade perch in the act of spawning.

By the way, this is the first time this species has been filmed in the act of spawning.

The hormone I use

Traditionally hatcheries had been using HCGto induce spawning.

HCG is used for a wide variety of fish, including goldfish, rainbow trout, seabream, catfish, and largemouth bass, etc.

For those interested in a deep dive into science of how this works, start here

I tried something different.

The hormone I tried was one I imported to spawn some of the more difficult Australian native freshwater fish that had never been spawned before, such as freshwater archer fish.

Click the picture to go to my YouTube playlist about archer fish.

It is a potent ovulating/spermiating agent used to promote and facilitate reproduction of many species of fish.
It causes the female to ovulate and it also promotes the production of sperm in the male.
It induces maturation without affecting viability or fecundity, resulting in highly predictable ovulation, with high egg fertility and viability.

The product also contains a dopamine inhibitor. (For those that want a deeper scientific explanation, click here.)

This dopamine inhibitor helps to prevent the fish from resorbing the oocytes as a result of the stress caused by the handling during the hatchery process.

This process is called atresia click for the science.

This is a process where the fish breaks down unspawned or developing oocytes to conserve energy, especially under stress, poor environmental conditions.

Remember, these species come from an environment that can experience sever extended drought conditions that can last for years, especially jade perch.

The female fish produces the oocytes, then if the environmental triggers fail to happen, she takes back the energy used to produce the oocytes, which may often save her life when conditions are bad in that part of Australia.

Just to make it clear - the hormone does not cause the female fish to produce oocytes.

No hormone does that.

What it does is provide the hormone that the fish would naturally produce when the final environmental trigger happens, sustained flowing water.

That is the hormone I inject into the fish, the ovulating hormone.

It ovulates the existing oocytes, then the fish will spawn by them selves.

No stripping of oocytes or sperm.

That does not work for Australian native perch.

So . . . how do you make the female produce the oocytes?

That is another subject - Management of Breeders - which can be found in the members area.

See this video where breeders are selected at the conditioning pond and taken to the hatchery for examination and spawning.

(3 minutes 11 seconds)

To summarise

Australian freshwater perch need three environmental triggers to spawn.

1. Rising water temperatures

2. Change in the type of food available

3. Sustained flowing water

A final factor is the sustained flowing usually results in flooding which results in plankton production thus providing food for the larvae when they hatch. See this video about plankton production in aquaculture

It all fits together like a jigsaw puzzle.