Fish Farming - Managing The Ova And Alevins
Do It Yourself Aquaculture Fish Farming - Managing The Ova And Alevins
By Vin Hayes
Should you buy eyed ova or collect your own? How do I take care of the ova and what do they require? What are alevins and what do I do with them? All fair questions for the novice aquaculturist to ask. Those small little eggs seem so fragile, don't they? They are, but you can handle them with a bit of instruction.
For the do-it-yourself aquaculturist with a stock of eyed ovum, it is time to really get started. The rearing boxes need to already be resting in the ponds for several weeks before the ova are ready. The edges of the boxes will be about six inches above the water and the box itself is moored so it won't move.
Now it is time to hang the hatching trays. The trays are hung inside the rearing boxes with the h2o level coming up to the top edge. This is where your ova will be calling home until they hatch and are strong enough to swim out into the rearing box.
The ova will need to be carefully washed before they can be added to the hatching tray. The technique for cleaning the ova is quite simple. A large container is filled with water and ova, the water is drained off and clean water added. This process is repeated until the water runs clear.
After cleaning, the ova can be placed on the hatching trays. This can be done by tenderly ladling the ova, a few at a time, out of the cleaning container. Hold the ladle very close to the tray and empty the ova as gently as possible. Never pour the ova from a height, the impact will certainly kill them.
Ova will hatch at a far higher rate if they are distributed into a single layer. This is a very delicate procedure and requires a gentle touch. A feather is just the tool for the job. Gently running the feather over the ova will spread them out with minimal damage.
Despite taking all the necessary precautions, some of the ova will die. They can be easily ID'd by their white or opaque color. Dead eggs must be removed from the hatching trays immediately. Leaving them in the trays can lead to fungus growth that can damage your entire stock.
A natural way to clear out dead ova is to introduce fresh-water shrimps to your hatching trays. They will only feast on the dead ova and will not damage live ones. These mini aquaculture housekeepers will clear out animal and plant debris in the water too.
Keeping a lid over the rearing boxes will also help to protect ova from fungus growth. Fungus loves light and a lid will cut off the light and keep growth to a minimum. A lid is also an excellent way to protect ova and young fish from predators.
In a short time, the first fish will begin to hatch. These young fish, also known as an alevin, will have a large bag on their underside. This is the yolk sac. The fish will require no food to start with. They'll feed off of their sac for the next month and a half or so.
Eventually, the do it yourself fish farmer will see that some of his alevins have begun to move away from the pack at the bottom of the hatching trays. They'll start to swim up towards the current. Now is the time to start feeding them finely processed meals. Their yolk sacs are almost gone now and they are moving on to the next stage of their lives.
In the next report of this series, we'll check out the "fry" stage of fish and the steps the do it yourself aquaculturist does to ensure their survival.
Go from Fish Farming: Ova And Alevins to Part 6: Fish Farming: Fry Care and Feeding
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