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Guest Julio

Fry Mortality Rate

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Guest Julio

My fry are now about 3 months old and the mortality rate seems high. I have read this is to be expected due to the genetic makeup of the fish - orandas. They are outside in 200 gallon filtered tanks with regular water changes.

If this mortality rate is normalish i am OK with it - nature I guess trying to keep control?

Can anyone shed some more light on this for me - thanks

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How many fry originally & how many now left? What's your feeding & water change regime? Are they kept with other fishes?

From what I've read, the mortality rate for goldfish fry if kept & cared for properly is very high. Even the deformed ones will survive enough food & space is there.

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I do know that fry need to be fed fairly constantly (green algae is great for grazing) and if they don't have enough I'm afraid the smaller fry become snack potential. Some larger fry will eat smaller fry. If the fry are mostly the same size then as the above poster says it may be another issue or genetic. Some combinations of fish genes can produce constitutionally weaker fry.

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Guest Julio

water changes regular and plenty of food. I have been constantly culling them but of the original spawning I would have only half left. They are not kept with other fish and they are similar sizes are kept together. They are Orandas so there is probably a lot of genetic influences coming into play.

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water changes regular and plenty of food. I have been constantly culling them but of the original spawning I would have only half left. They are not kept with other fish and they are similar sizes are kept together. They are Orandas so there is probably a lot of genetic influences coming into play.

Genetic influence does not have any big bearings on the survivability of the fry. Orandas is one of the hardiest fancy so I would very much doubt that it's genetics that caused the high mortality. Ranchu breeders that I know have close 100% survivability rate in their spawnings.

How regular do you do the waterchanges? And what kind of food do you feed them?

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Guest Julio

I am doing about 25% water change once a week - 250 gallon tanks - feeding daphnia and crumbled trout pellets. Does that sound OK? They are outside

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When u said "250 gallon tanks" u mean there are more than one 250-gallon-tank, right? How many tanks are there and how many fry have u got?

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Guest Julio

I have two 250 gall tanks that are filtered with a pond type filter with UV. I have about 120 half inch long fry in each tank.

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There do seem to be some common "die-off" ages in spawnings. These are commonly around 5 weeks, 8 weeks and 12 weeks of age. It is thought that this occurs at these times because the genetic makeup of the little fish is somehow compromised and, while little they can live, but as the body grows, it no longer can cope with the demands of life.

These genetic flaws are often called "fatal". For example: The fish may have a compromised digestive tract. While little, it can process enough food to feed the fish, but as the fish grows, it can no longer process enough. The fish will die. There are literally thousands of such problems that can occur - in varying degrees - within the genetic structure of a fish - and the range within a single spawning can be very wide.

Some lines of fish that are "well bred" have almost zero mortality from such genetic flaws. Other lines - most commonly from unrelated fish - are chock full of "fatal combinations".

I bred several lines of Broadtail Ryukins together. One cross yields nearly 80% fatal flaws. The other is almost the opposite - with nearly 80% of relatively "good" offspring. My Lionhead fry this past year were even "better" - yielding nearly 95% "good" fish...... I sold the lot of them for over $500!!

If, at age 3 months and above, you are still getting significant die-off in fish that were healthy and growing well, I would look for another reason......

Could you have parasites in the system? Hydra is a common predator that can inhabit fry tanks kept outdoors.....

With 120 fry per 250 gallons, you have a fairly intense rearing situation. When you have that many fry in a smaller space, they do tend to grow less uniformly - selecting for the fry that are least sensitive to environmental influences. These "insensitive" fry will outgrow their spawn mates, quickly turning to cannibalism. It is better to give all the fry the best you can - to even out the growth and competition. You will end up with more successful fry.

IT is suggested that you keep between 7-10 fry per cubic foot of water at the size you describe. They grow substantially during the week - and each week, new culls must be made to maintain sufficiant growth in the remaining fry.

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Guest Julio

Thanks for that Darryl - really helpful. One thing I was wondering - would I need an airstone in these tanks? I havent done it because I figured there was enough surface area.

How would I deal with parasites if I have them?

again, many thanks for your help

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