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Thread: Cannibalism, Tobi Fry & Ramblings

  1. #1
    Daihonmei MikeM's Avatar
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    Cannibalism, Tobi Fry & Ramblings

    It was commented elsewhere that cannibalism among koi fry is linked to low levels of live foods in a grow-out pond. If a lot of food is available, cannibalism supposedly does not occur.

    This past weekend our local koi club met at the home of a member who converts his swimming pool into a grow-out pond during the winter months when the family won't swim in frigid 70F temps. [ This is Florida !! :lol: ] He has observed that tobi fry stop cannibalizing when the small fry reach about a half inch or so ... about when pelleted foods are regularly available? The pool has a lot of algae, but not to the extent of a mud pond grow-out, and insect life was not particularly observable.

    This afternoon I got a call from some water gardeners from Minnesota vacationing here. They came over to see my pond late in the day ... great excuse to skip out of the office a bit early. They were definitely gardeners, rather than koi kichi. More impressed by a home-grown 9 year old Hariwake than the good ones ... But, the plant aquaria got their attention. In one a killifish I've been keeping (A. gardneri, for those who care) has been spawning. There are a couple of dozen fry of various sizes. This species spawns over a period of several days, so fry of all stages are together with the parents. I am sure there would be cannibalism if they were not well fed, but not in this tank. Adult live brine shrimp several times the size of of any of the fry are consumed greedily by the parents and largest fry. The small fry are left alone ... even the fry among the shrimp trying to figure out how to eat an animal many times larger. [Cute to see.]

    My guppies will eat their own fry when first born, but once the fry are swimming at the surface among some floating plants, the cannibalism stops. Adult live brine shrimp hiding in the same plants are hunted down.

    I have raised piscevorous species that would slurp up anything that moves... and many fish cannot recognize eggs as the next generation. Curious how Mother Nature has arranged things.

    Don't know if Tobi fry cannibalize because sufficient food of proper size is not otherwise available. Nice to think it is motivated by the necessities of survival, but that's a fuzzy-minded approach. At the same time, I've kept little tosai and even guppies with the big guys & never had cannibalism or "guppy-murder". A pond visited recently had very hungry under-fed koi accompanied by little mosquito fish. No mosquito fish were being consumed, even when swimming in front the hungry koi's mouths. Koi are so docile, I tend to think cannibalism is contrary to their nature simply because fish are not seen by koi as being food. But, among fry engineered by Nature to eat & grow to avoid being consumed by other predators, it is different. ... at least sometimes. Curious.

    Rambling with no purpose .... 8)

  2. #2
    Sansai Bancherd's Avatar
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    Koi are so docile, I tend to think cannibalism is contrary to their nature simply because fish are not seen by koi as being food. But, among fry engineered by Nature to eat & grow to avoid being consumed by other predators, it is different. ... at least sometimes. Curious
    Only tobi's should naturally survive without human intervention? :?:

  3. #3
    Tategoi
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    I have (soon to be had) a mixed pond; koi and goldfish. Last spring I had a few new tosai in my small Q-tank. At the same time I noticed some fry from some random spawning in the main pond hanging around the skimmer so I scooped them up using a fishnet made for tropicals and put them in the Q-tank that evening.

    The next morning all the fry were gone.

    I thought I was feeding the tosai enough. :roll:

    The rule of thumb I came up with was: if it fits in the mouth easily, it gets eaten. Or the close second: if it isn't recognized as a fish, it gets eaten.

  4. #4
    Daihonmei
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    Bancherd,
    Quite right to question that bit.....The accepted opinion is that in the case of a large number of offspring thaat diversity of size increase the survival rate of the total of the spawn.
    Some of the ways are by the variation in size making it difficult for a specific predator size to effectively eat all the offspring. And another is that by some offspring eating the younger and growing larger the larger offspring will eat other food types and will not compete with the small fry. This will also lessen the pressure on the fry food supply by reducing the number of fry in two ways; predation and growth.
    There are several other dynamics but that gives some "food" for thought.

  5. #5
    Nisai Sanke56's Avatar
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    I have seen this cannibalism in young koi and those big guys need to be removed. They are big as they eat anything they can. Koi like live food moths etc that fly into the pond and will eat small koi but don't make a big effort to eat their own kind. In 2002 I put 100 fry in another pond with lots of weeds etc and dapnia[small almost microscopic animals] and at first I thought the big guys ate them all but in fall when I emtied the pond there were nearly 100 little guys and they were the biggiest from the whole spawning so I would say from this that the koi are not highly cannibalistic like some other fish cichlids etc that I have raised in the past.
    This pond is likely 30,000 gallons mud bottom with lots of weeds and there were 20-30 8-10 inch kio in there to grow out. The fry were about 1-2 weeks old when put in there free swimming but only 1/2 inch long no color differentiation yet.
    The perfect koi is always one purchase or spawning away!

  6. #6
    Nisai Mike Snaden's Avatar
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    Could this be called involuntary cannibalism?

    The food being thrown in here, is actually culled fry from the day before. This may seem a bit harsh, but the options are to either throw them in the river and overload the river systems (if any survive), or overload the refuse sites. This feeding regime only happens using fry of up to about 2cm. Bigger fry always get a sporting chance in the river. It seems that even breeders have a concience once they see hundreds of cute little eyes and mouths looking up at them! ;-)

    Mike.

  7. #7
    Jumbo
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    I would predict that the advent of KHV in Japan will soon the make the dumping of culls/fry in the local rivers illegal. JR

  8. #8
    Oyagoi
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    Dumping koi in rivers...

    Probably is illegal and has been for some time. Most countries with aquaculture industries have laws against escapement.

    Funny thing is, it isn;t illegal in Texas (where everything else having to do with fish is against the law).

    A few species can be placed into public waters without a permit, including common carp and goldfish as well as several other species of cyprinids. This was done so to allow for the sale and use of live fish bait in public waters.

    Of course I managed to put this loophole to work.....

    A small municipality wanted to stock some koi in its local waterway that ran through town and recieved treated domestic sewage. There were aquatic weed problems and no permit for grass triploid carp would be issued as the waterway emptied to a river. Koi work almost aas good as grass carp with respect to many aquatic weeds. For some reason they are much better weed eaters than the local common carps from rivers.

    Anyhow I called and asked the state boys if I could put koi in that waterway and they gave me an unequivocal, "NO." I protested, rule book in hand that it was legal as koi were indeed the same species as common carp and the rules are administered "by species" (determined some years earlier in a ruling that benefitted the state's desires at the time).

    We read the book together over the phone....it seems when we turned the page we got the rest of the rule.....along the lines of, "No law restricting the placement of the following species (list is short, includes carp and goldfish) into public waters.....turn page.....WHILE FISHING shall be enacted.

    Well, that was easy enough for me to fix. I told the state boys I would not be applying for a permit and would be stocking the fish, told 'em when and where. My helper would unload the truck while I fished along the bank. They left me alone.

    But....nowadays the implications are bigger than just exotic species contamination. Of course the state boys get wind of a species specific pathogen like KHV and they might be replicating and releasing it into the waterways in order to reduce the overabundant carp populataions. That would not be good for Texas koi keepers.

    My response to these pathogens has been tight biosecurity. No surface water pumped up to the farm, only ground water (bore hole water to yall Limeys). No fish in the gate, only fish out the gate. Not even any new breeding stock this year. In previous years new breeding stock has been quarantined off-site for six months prior to intro to the farm. None to come in ato my place at all this year. I'll wait and see how things shake out in Japan this summer before taking on any new specimens.

    A word to American hobbiests....Worst thing you can do for the hobby is to turn lose unwanted koi into local waterways. As they keep turning up where they do not belong, the guvment and eco-folks will do something to keep them out, like make them illegal altogether.

    In Texas, an ornamental fish dealer (includes tropicals) must take back any unwanted fish they sold to a customer. They don;t have to pay for it, don;t even have to keep it alive, they just need to take it off the hands of the hobbiest that no longer wants it. Keeps them from ending up in the creek.

    Brett
    Brett

  9. #9
    Jumbo
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    Ha! Great story and good public service announcement. Brother bil must be having heart palpitations over that underwater weed story ! JR

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