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4CornersPuddle, gehajake, jpsdad, Sunil, wbuffetjr
Total Likes: 15
Original Post (Thread Starter)
#540445 10/09/2021 5:41 PM
by Pond Star
Pond Star
[Linked Image]Have a small 60' x 70' pond with minnows, mosquito fish, and crawdads. This is what the water has looked like the last 3 weeks (split pea soup) - even with adding some clean river water every few days. I have two larger ponds - 1/2 ac and 2/3 ac and never see anything like this in them. Is this a matter of too many fish (50 or so minnows, 500 mosquito fish, and unknown number of crawdads) for such a small pond ....................or ??
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#540513 Oct 12th a 12:26 PM
by jpsdad
Originally Posted by esshup
jpsdad, given that there is P in the food. how much of that P in the food is retained in the fish? (to grow the bones, scales, etc.)

That's a great a great question esshup and its one that I have been seeking. Its complicated but I will share some things that I am learning from available research documents.

First, it in part it depends on the fish. Some fish put more investment into the structures that require P. For example, BG and LMB put more investment into scales, fins, and bones than to rainbow trout.

Second, it "might" partly depend on the concentration of P in the feed. One reference stated findings that a reduction from 1.2%P to 0.8%P led to a 33% decrease of P in effluent in a rainbow trout facility. Interesting thing is 0.8 is 1/3 less than 1.2% and so it would seem the amount retained is to some degree dependent on the amount consumed.

We can make a ball park estimate of P retained from FCR. For example, for 1% P feed with FCR of 2 and a fish whose dry weight is 20% and whose dry weight concentration of P is 1.5% the P Consumed and retained is:

Pcon = .01 per lb feed consumed

Pret = .2*.015/FCR = .0015 per lb feed consumed

So the proportion retained is:

PropPret= .0015/.01 = .15 or 15% is retained, 85% discharged in feces

This proportion of retention keeps pretty well with the 10% assimilation rule. In the example above, the proportion of P in feed is less than that of fish and so the calculation is greater than 10% retention. It is probably more accurately somewhere between 10% and 15% retained and 85% to 90% discharged.

Some other interesting facts. Increasing P in feeds creates leaner longer fish and reduces conversion efficiency (increases FCR). Decreasing P in feeds creates fatter (higher lipid content) shorter fish and increases conversion efficiency (lowers FCR). Above we a assume a minimum P is present in the feed below which the metabolic needs for P are not met. This particular circumstance is very interesting to me. A low P feed might produce slower growing ... more energy dense prey for predators than a high P feed. A high P feed might produce fish more capable of reaching trophy potential because it better builds the frames trophy fish have.

There is a lot more to learn here. But some of the answers to questions I have be exploring are coming to light. One of things I have learned, for example, is that harvesting fish cannot meaningfully control P additions unless the P additions are pretty much the same as P in the harvested animals. For example, feeding 100 lbs of feed will add 50 lbs of wet weight fish to your pond but to remove the P of 100 lbs of 1% P feed one must remove more than 300 lbs of wet weight fish (whose dry weight P is 1.5%). So I retract any prior statements that fish harvest is part of adequate control of nutrient accumulation. It hardly makes a difference at all. One of the keys to science is to listen to evidence and to allow evidence to reshape one's thinking. One must be ready to abandon a preconceived notion ... no matter how much sense it seemed when first conceived.

The evidence clearly demonstrates there is no way to manage P introduction with harvest unless other organisms convert the P in feed excrement into food for the harvested fish. In the example above, this would require a whole pond FCR of .333 where 250 lbs of the gain from the necessary harvest came from pond organisms utilizing the waste P. What this tells us is that P addition requirements are very low in a harvested system where Sun and native nutrients are providing the food for growth each year. Most systems naturally accumulate more P than required to replace the P in harvests that are appropriate for balanced populations.
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#540646 Oct 15th a 01:47 PM
by wbuffetjr
Jpsdad - I also much appreciate your posts. My water is very eutrophic even though it has never seen a single pellet of feed. I have chara coming out of my you know what. The phosphorus content of my water is high coming right out of the ground so nutrient removal is going to be something I deal with forever. I am becoming very interested in the topic. Once I achieve reproduction , my initial target was to remove 200lbs of fish per year starting in year #3 after reproduction and then evaluate/adjust from there. I should be able to add some pounds of crayfish on top of that. After reading some of your posts it sounds like that might not be enough to make a dent in the phosphorus load.

I learn something new everyday! I had no idea crayfish were so high on an energy density list. I have to imagine that fatheads, another component in my lake, are rather low in energy density. This gets me excited to see what kind of growth my Brook Trout will see off of these guys!! Doesn't take too many this size to make one pound of crayfish.

[Linked Image from i.imgur.com]
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#540669 Oct 16th a 07:54 AM
by jpsdad
I'm trying to figure out if the Colorado Koolaid can is 16 oz or 12 oz. Not for sure if my memory is correct but didn't Coors once sell a 14 oz can?

Anyways, the crayfish are large. It will interest you to know that the dry matter of all living things LESS the mineral content has a very close relationship to energy content ... at least for those organisms that have be tested thus far . Most of the minerals are calcium and phosphorus with other minerals in smaller quantity. The correlation to this relationship is so tight it has an R-squared >=0.97 (where perfect correlation is 1.0). This is suggests that energy content of wet weight samples can appropriately be determined by finding the ash free dry weight of a sample. A surrogate method that is much easier to do than determining its caloric content. Essentially the dry organic compound percent of the wet weight determines this value. This makes sense when you think about it. The sun powers the formation of organic molecules ... it is in these molecules that all of the energy is stored.

So the dry matter of BG less its ash is very closely as energy dense as the crayfish's. However, I think crayfish are superior prey than BG for a number of reasons (provided a predator is eating them). First they can achieve higher wet weight standing weight. In an unfed unfertilized control Paul Brown et al grew 800 lbs/acre of Northern crayfish in 5 months. BG under the same circumstances would have been limited to around 500 lbs/acre but only if the water was so fertile it would have been as productive as one that is actively fertilized to maintain bloom. So crayfish can produce 60% more wet weight forage per acre than BG. Produce is the key word here, literally the 1 season potential for gain in standing weight is at least 60% more. In a cropped system, this production could exceed the potential standing weight but that is a whole other topic smile Couple higher wet weight production with 50% more energy in the wet weight and hey we are talking more than twice the energy to consume of (possibly easier to catch) prey. It would just make sense that LMB would ignore BG when crays are abundant.

So why would crayfish have higher energy content than BG? I can think of a few possible reasons.

1. They are benthic organisms that do not need buoyancy and probably benefit from having higher dry weight percentage and negative buoyancy. Nature probably selects for this greater dry weight percentage of wet weight.

2. They don't have as much investment in structures requiring minerals. So the ash content is lower.

3. The lower investment into structures requiring minerals may allow the crayfish to invest more in storing lipids which reduce wet weight are very energy dense (more so than proteins for example)
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#540785 Oct 19th a 11:08 PM
by Pat Williamson
Pat Williamson
They just guard craws keeping someone from getting his beer
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#540565 Oct 13th a 08:47 PM
by jpsdad
Originally Posted by gehajake
That being said, It seems like I read somewhere on a thread on this sight that they are inferior quality of a food source ...

Gehajake, I used to think that because I read it here. But subsequently a chain of events changed my mind. Ewest introduced me an article on Pike in Arizona where there is a rogue population of Northern Crayfish that has been introduced. In the lake with the highest growth, the pike preyed predominately on crayfish in the spring and carp in the summer. They listed the wet weight energy content of multiple species as measured by various authors. Both Northern Crayfish (the kind QA has) and Carp are significantly more energy dense than Centrarchids. Because these values were determined by standard experiments, I elected to change my mind and accept as true that Northern Crayfish are better quality food than BG and allowed the unanswered question that WRC or RSC may also be too. Below is the table of wet weight energy densities:

[Linked Image]

... I dont know about that but my CC are doing extremely well, also in an older strip pit that I fished in a lot we would catch huge bass, we never did check any of the large bass but any bass we culled had craws in them and a Strike King rubber craw was their favorite lure, I still fish a lot with them to this day. but that was before the otters cleaned that pit out. they are slowly coming back and we are being able to catch a few again

Although this evidence is anecdotal, it is evidence that crayfish presence does not prevent your CC from exceeding expectations or LMB in that strip pit from becoming huge. They appear to be very good forage for both CC and LMB as your experience exemplifies
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#540547 Oct 13th a 01:50 PM
by gehajake
I m with Augie, I dont think theres any way to keep them out of your pond. it all depends on what you do with them when they arrive. With the introduction of CC in QAs pond I think he will see a drastic drop in their numbers.
I got some of the craws from QA only to discover there were already a ton of them in my new pond. every one the young CC I caught were full of crawfish, they love them and I suppose can catch them pretty easily, I opened the stomachs of the CC to see what they were consuming and pretty much 100% of them had crawfish present.
That being said, It seems like I read somewhere on a thread on this sight that they are inferior quality of a food source, I dont know about that but my CC are doing extremely well, also in an older strip pit that I fished in a lot we would catch huge bass, we never did check any of the large bass but any bass we culled had craws in them and a Strike King rubber craw was their favorite lure, I still fish a lot with them to this day. but that was before the otters cleaned that pit out. they are slowly coming back and we are being able to catch a few again.
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#540657 Oct 15th a 07:18 PM
by canyoncreek
Nice touch there wbjr,
I love the double meaning of the slogan on that choice of beer can to put in the picture. Born in the rockies also applies nicely to those giant crayfish too!
You sure your trout can eat crayfish that large?
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#540678 Oct 16th a 08:17 PM
by FishinRod
Originally Posted by wbuffetjr
Doesn't take too many this size to make one pound of crayfish.

[Linked Image from i.imgur.com]

Great job growing the monster crawdads!

Very impressive that you trained them to drink beer. (Of course it was probably easier to do since they have a can opener on each front appendage!)

Noob question:

Why did you teach them to drink light beer? Wouldn't they gain weight better if you had them drink the full-calorie good beer?

Or are you keeping that beer for yourself? grin
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#540668 Oct 16th a 07:16 AM
by esshup
A lake in Northern Wisconsin that I fish (and shall be left nameless because the WI DNR says that there are no SMB in there) had Rusty Crayfish introduced to it somehow. They pretty much completely denuded the lake - very few submerged aquatic weeds in there now. At night if you take a flashlight and shine it on the bottom of the lake there is a crayfish walking around for every square foot of pond bottom, maybe more.

Smallmouth look like pellet hogs. Last one I kept from there was 19" long, 19" around and weighed 6#.
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#540822 Oct 21st a 02:33 AM
by canyoncreek
esshup, I'm with you on the Rusty Crayfish situation. I understand that the goal is to prevent invasive species, but when the rusty is as common as anything else already in our lakes it seems a little too late to hang up posters or think about checking someone's livewell in case one is hitchhiking.

The fear is that they will outcompete smaller less aggressive native crayfish which also is probably true but it seems we are way beyond that already in lakes around here. A large lake loaded with Rustys in Northern lower MI also has seen the population of SMB and YP adapt. The fish are hefty and even the 6-7" YP we would catch would have surprisingly large rusty crayfish folded up in their stomach. This lake has few LMB but I would have to believe the LMB would have an easier time foraging on the largest crayfish than even the SMB do.

I do wonder if rusty crayfish need more calcium content in the water in order to spawn? I know this lake must have tons of natural limestone and high calcium content as every dock or rope left in there will get a gritty stone grime attached to it very quickly. The crays flourish. Lakes with 'softer' ground water chemistry don't seem to struggle with as much rusty crayfish reproduction.
1 member likes this
#540818 Oct 20th a 11:56 PM
by gehajake
Originally Posted by Pat Williamson
They just guard craws keeping someone from getting his beer

Man Ive seen the day when Id like to had a couple of them in my cooler to guard my beer, could be a good time, conversation starter, especially after dark.

Now my wheels are turning, this could be a fun experiment.
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