Thread: Ask the Biologist

Question for Craig,

When a fish dies in a lake instead of by fillet knife, what determines if the fish will sink to the bottom of the lake or float to the top and wash up to shore? You always see a fish or two dead up along the shoreline, but alot more fish just have to die from old age than the one or two dead ones you see. My best guess was that the fish that die naturally sink to the bottom and never are seen but the fish that die from sickness end up along the shore line blotted.

This came up talking to a buddy about the twenty some pound bass in California "Dottie" that was found on the shoreline a year or so ago. And the white bass fish kill that Cheney or Marion had several years back where fish were scattered on the shoreline.

This is great.Thanks Craig for giving your time to the public like this..I have a question about a microscopic invader called Daphnia lumholtzi, I became aware of it by a guy named Dzialowski. In his speech he talked about how it is being found in kansas more frequently and how it gets into a fishes mouth and can actually chokeon them. I was wondering if this little guy is something we need to be woried about in our reservoirs and rivers and if so what can be done to prevent/eradicate it?

Originally Posted by fishingtim

Question for Craig,

When a fish dies in a lake instead of by fillet knife, what determines if the fish will sink to the bottom of the lake or float to the top and wash up to shore? You always see a fish or two dead up along the shoreline, but alot more fish just have to die from old age than the one or two dead ones you see. My best guess was that the fish that die naturally sink to the bottom and never are seen but the fish that die from sickness end up along the shore line blotted.

This came up talking to a buddy about the twenty some pound bass in California "Dottie" that was found on the shoreline a year or so ago. And the white bass fish kill that Cheney or Marion had several years back where fish were scattered on the shoreline.

fishingtim,

Some diseases do cause a fish to "float" at the top of the water as the disease can effect the air bladder of the fish, but not all diseased fish will float and not all fish that die of natural causes will sink.

A big factor in this float/sink question is the temperature, both of the air and the water. At warmer temperatures, decomposition occurs more quickly and will cause a fish carcass to bloat up and come to the service where they are visible. At cold temperatures, decomposition takes place much more slowly and not enough gases may be produced to float the fish to the surface. This is seen in winter roadkills vs. summer roadkills. A roadkill deer will bloat up in a matter of hours in summer but will take days in winter.

Scavengers must also be taken in to consideration as they can clean up dead fish very quickly. Even if they scavengers cannot eat the fish whole, they may make a hole in the skin of the fish which releases the gases floating the fish and the fish will sink. In the summer time fish decompose VERY rapidly and a 5 to 10lb fish is reduced to "soup" in a matter of days.

Easy meals don't last long in the fish world. Sick or dying individuals are picked off quickly by fish or other predators/scavengers. Large scale fish kills produce many easily seen dead individuals, but there are also large numbers that are not easily seen.

Originally Posted by cannon14

This is great.Thanks Craig for giving your time to the public like this..I have a question about a microscopic invader called Daphnia lumholtzi, I became aware of it by a guy named Dzialowski. In his speech he talked about how it is being found in kansas more frequently and how it gets into a fishes mouth and can actually chokeon them. I was wondering if this little guy is something we need to be woried about in our reservoirs and rivers and if so what can be done to prevent/eradicate it?

cannon14,

Yes it is something to be concerned about and the KDWP message of CLEAN DRAIN DRY will prevent the spread of the exotic waterflea and other aquatic nuisance species (ANS). Like most ANS, once they find their way in to a water body it is very difficult (usually impossible) to eradicate them.

Here's some info taken from the KDWP ANS Plan.

The following ANS species are considered of special concern in Kansas; bighead carp, black carp, exotic waterflea, New Zealand mudsnail, round goby, rudd, ruffe, rusty crayfish, silver carp, spiny waterflea, white perch, and zebra mussel. Currently, the zebra mussel, white perch, bighead carp, silver carp, black carp, and New Zealand mudsnail are considered priority species.

Exotic waterflea Daphnia lumholtzi. Native to Africa, Australia, and India, this species was first discovered in 1990 in Texas. It has since been found in several Midwestern states including Kansas. Analyses of pre-invasion zooplankton communities indicate that D. lumholtzi may be invading reservoirs in which native Daphnia species are rare. While the long-term effects of the invasion of D. lumholtzi are unknown, it has the potential to dominate late summer zooplankton communities in eastern Kansas reservoirs (Dzialowski et al. 2000). The presence of D. lumholtzi in some Kansas reservoirs indicates a need to monitor invaded reservoirs to document the range expansion and determine the long-term implications of the introduction of this invader.

There are several several waterfleas causing problems throughout North America: Spiny waterflea (Bythotrephes longimanus) fishhook waterflea (Cercopagis pengoi) and exotic waterflea D. lumholtzi. All of these are transported in lake water which reinforces the importance of following the CLEAN DRAIN DRY recommendation.

Several of you are probably familiar with the spiny waterflea and the impact it has had on the Great Lakes. These critters gather in such large numbers on fishing lines that they can actually foul the line and reduce catch rates.

For more info on the exotic waterflea, click HERE.

Craig, Thanks for your reply about the dead fish. Sound like the circle of life takes care of the fish pretty well.

So a follow on question. If I have the option I will usually clean the fish I keep at the lake to "keep the mess at the lake", then just throw the fish bones in the lake for catfish or crawfish to eat the left overs and finish decomposing.
Is this the best thing to do with the carcass or should they just be thrown in a dumpster?

Originally Posted by fishingtim

Craig, Thanks for your reply about the dead fish. Sound like the circle of life takes care of the fish pretty well.

So a follow on question. If I have the option I will usually clean the fish I keep at the lake to "keep the mess at the lake", then just throw the fish bones in the lake for catfish or crawfish to eat the left overs and finish decomposing.
Is this the best thing to do with the carcass or should they just be thrown in a dumpster?

fishingtim,

Most State Parks, Corps Parks, and users of these areas would prefer that no fish parts are placed in the dumpsters. As everyone knows, fish get RIPE very quickly and no one likes the smell of rotting fish!! Dumpsters are not a good place for fish parts.

Some lakes have fish cleaning stations located off of the water and these keep fish wastes confined and the stink is minimized through the use of holding tanks/sewer systems. Depending on the lake you are at, dropping your fish parts off at the cleaning station may be an option.

Other lakes have more primitive fish cleaning stations which consist of a board and pitcher pump mounted on the boat dock. Fish heads, guts, and skin go back in to the lake under the dock which also minimized the mess and smell. Fish and turtles quickly clean up the fish parts left at these cleaning stations.

If done correctly, putting the left overs from your days catch in the lake will not cause any problems. If you have caught your 50/day limit of crappie and you dump a bushel basket full of heads and guts on the shore right next to the boat ramp, there will be problems!! I have seen cleaned (filleted) catfish bobbing next to ramps or shorelines that still have the abdominal cavity and air bladder intact which causes them to float and rot and stink and cause a nuisance to any one in the area. These fish carcasses should have been taken away or at least had the air bladders punctured so the carcasses would sink. Deeper water is also necessary to dispose of the fish leftovers-- no one wants to see a mess of fish on the bottom in 2 feet of water right off a ramp or campsite.

If you do clean fish at home, put all the heads/guts in a plastic bag and freeze them. Then when trash day rolls around, throw them in the trash. Stink will be minimized and your trash man won't be mad!

We have many different lakes in Kansas and some are run by City, County, or other entity. You may be ahead by asking staff at the lake you are at that what their preferred method of fish disposal is as regulations can vary.

I agree it's pretty discusting to see and or smell rotting fish around the lake shore.

I typically clean my fish at home and freeze the carcas like you recommended. The only problems is getting my wife to agree to let me put a bag of dead fish right next to our food and remembering to throw them out on trash day, but she sees the benefit of no smell. As long as I don't end up having fish head soup for dinner. haha.

Question Craig:

I have a question that intrigues me. General overview;

a) When I keep crappie for the knife, I pack them in layers on ice in a cooler. In the winter, I use the snow. I usually fish till dark and when I get home, unloading the boat and getting to the LazyBoy are top priorities.

b) I clean the fish in the morning with a fresh pot of joe. Fish are always just fine and there is no question up to this point.

c) Dec, Jan and now Feb, I notice a distinct variation in the white vs black crappie that I handle in the morning. The cooler usually has a mix ratio of about 5 whites to 1 black. I'm usually cleaning 14-20 crappie so there are always a few blacks in the bunch. The white crappie are quite firm but not frozen in the moring while the blacks are limp as though they just came out of the water.

d) This the case in every single instance. I have kept enough coolers of fish that the probability that the blacks didn't get "iced" quite the same is not a factor. When I say enough, I'm saying that since December, I have had probably 20, if not more coolers of fish to clean in the morning.

My interest is that there has to be a biological variation in the species that causes this specific difference. Have you ever heard of this? Do you have any idea as to the biological answer to this quandry? It is absolutely not a random chance occurance as I have been interested in this question going through far too many coolers of crappie.

If you don't have any ideas about this question, can you send along an email of an AFS (American Fisheries Society) member either at the state or national level that can help with the question.

Thanks