Waters & words

They grow bigger in the wild

We have known for some time that fish grow faster in a dam (Americans read pond/lake) than they do in the hatchery. A hatchery you see, is a business enterprise. And a business enterprise had best watch its feed conversion ratio if it wants to be successful. In other words the level of feeding required for an optimum feed conversion ratio, is not the same thing as the feeding required for maximum growth rate.

PB150080

Our local fishing club  for a long time stocked 2” fish, and something like 8 months later stocked a top up of 9” fish. But the club stopped doing that when fishermen were catching 10’” fish and 15” fish a month later. In other words the fish grew from 2” upwards much faster in the dam, than they did in the hatchery, and it made little sense to buy 9” fish, when you could rather buy them at 2” and grow them cheap the natural way.

I recently heard that Martin Davies, of Rhodes university confirmed this phenomenon, when they stocked different sized fish in this manner, but marked the one size with a notch in the adipose fin. Clever!  Then they could see which batch they were catching for the rest of their lives.

Of course after a year or so, the 2” fish are “wild” fish, and the stupid 9” fish are “Hatchery Harry”, with some ragged fins, and a lot less going for them.

So how far can you take this? What about stocking as fry? Will you get even better growth, and bigger fish when they reach say 12 months of age. I think so, but I also know that your mortality with fry is awful. So maybe there is a trade-off.

But here is another aspect to consider. If you take a child in a refugee camp at age 15, and compare him to a 15 year old ball player at an ivy league school, one is going to be a hulk, and the other will be built like a racing snake. That stands to reason. Now take these same two individuals at age 40. Which one will have the greater “condition factor”?

Now apply the same logic to the 10” fish and the 15” fish caught in the dam , one month and 9 months after stocking respectively. Do you think the 10” fish will ever reach the size of the 15” fish? I think not. I think that 10” fish is in some small measure, a runt. A runt by design. His formative months were spent on a diet designed not for maximum growth, but maximum profit.

So when someone tells me they are stocking 3 pound fish into their dam to create a trophy water, I have to bite my lip, and pretend to be impressed. But I do accept that this thing is an inexact science at best. I for one do not have all the answers.

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4 responses

  1. Years back I was involved in stocking some dams in the Kouebokkeveld, cold water dams in the high country with lots of food, virgin water really, at least in terms of supporting trout. I recall six inch stocked trout attacking tadpoles almost as big as they were within minutes of being released. The tadpoles formed a classical “bait ball” and it was like watching tuna hit a shoal of mackerel, just in miniature. Those fish grew at a rate that couldn’t be emulated in fish farm conditions. So I would imagine, that subject to there being sufficient natural food available “wild” trout will always win out. More to the point, they make for better angling, they behave in a more predictable manner and the angler fairs better using imitations of natural food forms rather than the flash of stocky bashing lures, something that to me at least adds to the experience. In reality for the angler the kudos of “big” fish should be related to their age, experience and difficulty in catching them. Large trout which were eating pellets in a blue porta-pool the day before may be fun but it is something of a hollow victory when you get right down to it.

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    February 5, 2013 at 7:20 am

    • Agreed Tim. Due to financial constraints, we stock some similar water with fry only. Visitors who catch these fish are always astounded at their strength. Thanks you for your contribution to the subject.

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      February 5, 2013 at 8:07 am

  2. I have heard that the 10″ fish haven’t developed the proper visual cortex. Maybe that is why they don’t grow as fast… I’m with you on the stocking, I’ll continue fishing our “ponds” over here for more naturally grown fish.;) Great info!

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    February 2, 2013 at 5:57 pm

    • I have assumed that the fish’s physiological development is the same in hatchery rearing as it is in the wild, and focused only on growth rates here, since that is the limit of my knowledge. Apart from worn fins from the raceways in hatchery fish, I have not witnessed significant developmental variances in Trout…just the growth rate differences. Thanks for stopping by.

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      February 3, 2013 at 12:04 pm

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