Pond Boss Forums Thread Like Summary - Latest PB Mag: Are trout useless forage?

Dr Wesley Neal had an interesting article in the latest PB magazine about rainbow trout as bass forage. While he acknowledged that LMB love trout and seem to grow especially well on a trout diet, he argued that stocking winter trout for the purpose of feeding LMB is mostly futile. Too much expense for too little LMB gain. He makes a good case, and I've had to reconsider my plans to stock trout in a few weeks.

I have something like 50 lb of LMB per acre, or about 400 lb for the whole pond. If I put, say, 100 lb of rainbow trout, and all get eaten by LMB, that would amount to only 1/4 lb per bass. Considering that, at best, only 20 percent of trout converts to bass flesh (10 percent is usual figure but trout may be better), that means 1/20th of a pound extra per bass. Not noticeable, and certainly not worth paying $1,200 to $1,500. And that's best case!

But leaves out a very important point: I don't stock trout to feed all my bass. My interest is feeding the large LMB, preferably over 18 inches. Based on creel results & electrosurvey, that might be 10 to 15 percent of the bass. (I wish it were higher, but that's life.)

Okay, so if top ten percent are my target, that would mean ten times 1/20th, or half a pound extra on each of my biggest bass. Suddenly I'm very interested.

Since trout get sluggish before expiring of heat in spring, probably the vast majority get eaten without much energy expenditure by the LMB.

Problem: How do I keep the 90 percent of smaller LMB from eating trout? Answer: The trout have to be large, 12 inches & up. Due to their fusiform shape, trout are more easily eaten than other fish.

Problem: Won't some of the 12 inch trout quickly outgrow forage size even for trophy bass? Yes, some will. Hard to quantify exactly. We can catch & eat the bigguns, so it won't go to waste.

Problem: Won't hybrid stripers also eat some trout? Sure, but that will still go toward sport fish.

Problem: Won't cormorants get some? Yes, sadly. Not much I can do about that. But remember that they also eat some LMB, mostly the smaller ones.

Right now I'm thinking maybe 100 lb of 10-12 inch RBT in main BOW, 70 lb 4 to 6 inchers in my forage pond. Feed small guys up until they reach at least 1/2 pound, then release 300 lb into main BOW.

That's my current thinking. If taxes and energy prices are going up next year, though, I may have to pull back. We'll see.

Comments?

I am going to look into this to search for info.

My guess is as follows based on my memory of several sources.

Water temps

39 - 50 F - RT have the advantage of mobility and active metabolism . The colder it gets the less active the LMB will be.

51- 70 F - equal footing - bass metabolism starts to ramp up and then equal RT. LMB can and will feed on RT with the amount increasing on a sliding scale as temps rise. RT will have active metabolism up to 70 F +-

70 F + LMB have the advantage and as temps increase the advantage increases.


Best guess for success if stocking smaller RT - stock behind a blocking net (habituation) when temp gets to 50 F and feed them high protein feed. After a few days as temps drop you can remove the net and keep feeding. Would be good to have cover inside net area for RT protection after it is removed. Watch and adjust as needed.

Additional info

The growth curves for largemouth bass derived from laboratory data (constant temperatures) indicated that growth is negligible below 10°C,
Is nearly linear in the range10-28°C, and declines abruptly above this
Value (Strawn1961;Coutant,unpublished report).

Largemouth bass consumed prey during winter at temperatures that were greater than or equal to 6°C. At less than 6°C, feeding continued infrequently. In our experiment, winter temperature drove much of the variation in consumption by largemouth bass in all winters. Metabolism of largemouth bass, like that of many fishes, declines with declining temperature (Brett and Groves 1979; Rice et al. 1983; Jobling 1993), likely contributing to reduced consumption. Although feeding continued through winter, it was infrequent below 6°C. Previous investigators have suggested that largemouth bass do not feed below 10°C (Markus 1932; Johnson and Charlton 1960).

Behavioral and Metabolic Adjustments to Low Temperatures in the Largemouth Bass (Micropterus salmoides)
Daniel E. Lemons
, and
Larry I. Crawshaw



Food intake was measured during and after the acclimation period, and MR and activity were measured following the acclimation period. MR, measured in a closed system, was exponentially related to temperature with a Q10 of 3.0. Food intake declined linearly down to 10 C, below which it became negligible. Spontaneous swimming activity, measured in an annular tank, was similar for all fish at or above 7 C and was considerably reduced at 5 and 3 C. These data indicate that physiological systems respond very differently to low acclimation temperatures in the largemouth bass. MR shows no compensation. The central nervous system, which mediates activity cycles, shows perfect compensation from 17 to 7 C, with a decline at lower temperatures. An energy analysis reveals that food intake fails to meet even resting metabolic requirements at temperatures below 10 C and that the net cost of spontaneous swimming activity is a small portion of the total daily energy expenditure from 3 to 17 C.

Bioenergetics and growth of largemouth bass (Micropterus salmoides) in relation to body weight and temperature
Authors: A. J. Niimi and F. W. H. Beamish


For most weights, growth of fish (grams/day) was highest at 25C, and lowest in fish at 18C. This was attributable in part to a higher satiation (maximum) feeding level at 25C. For a fixed level of feeding, growth rate (percentage wet weight/day) was highest for fish held at 18C.Lipid content (percentage wet weight) increased with feeding level and was highest at 18C, Moisture content varied inversely with lipid. Protein and ash content did not vary appreciably with temperature, body weight, or feeding level.Maintenance requirement of bass, expressed as grams/day, was about twice that lost during food deprivation, but only slightly different when expressed as kilocalories/day.Energy requirements for nonfecal losses were estimated as 10% of intake energy at all feeding levels. Standard metabolism accounted for 50% of intake energy near maintenance, but only 10% at the satiation feeding level. Growth requirements increased From zero at maintenance to 40% of intake energy at satiation feeding


The minimum temperature for growth in trout is about 38o F. At this temperature and below, appetites are suppressed, digestive systems operate very slowly, and trout require only a maintenance diet (0.5 to 1.8 percent of body weight per day, depending upon fish size). Feeding more than this wastes feed. In warm water (above 68o F), a trout’s digestive system does not use nutrients well and more of the consumed feed is only partially being eliminated. This nutrient loading of the water, coupled with the generally lower oxygen levels in warm water, can easily lead to respiratory distress. In warm water, feeding rates should be reduced enough to maintain good water quality and avoid wasting feed. The optimum temperatures for growing trout are 55 F to 65o F. At this temperature range feeding rates should be at maximum levels (1.5 to 6.0+ percent of body weight per day).

I had a thought.. I know, that's hard to believe.
What IF.. the trout start to slow and get sluggish after the big females (LMB) have already hammered their pre-spawn take and now want nothing during the actual spawning process? What if these 2 things coincide time-wise??

Frank, about half the cost is the trout and the other half is the feed if you choose and appropriate commercial trout feed. If you use optimal or purina formulations for predators, it will cost as much as former just for the feed. First, one needs to match the feed to the fish.

Feeding forage isn't a cost efficient way to grow predators. Feeding predators the feed directly is very cost efficient. The reason deals with conversion ratio of forage weight to predator weight.

I think feed targeted to raising appropriately sized trout will be more cost efficient than the same quantity target to feed large BG. I would think that the majority of feed of you are feeding BG is going into putting weight on the largest BG. That introduces inefficiency simply because the BG that directly benefit are the ones that the LMB can't eat.

But then feeding BG produces manure and this manure stimulates the base of the food chain creating a bloom of micro-organisms. It is this bloom that provides cover to young BG fry and lots of food. And so production BG YOY is what is going to grow your LMB. So this begs the question, if the "REAL" benefit to the LMB is a secondary effect of feeding .... is there a way ... to shift the use of feed to another organism so that the primary consumption of feed grows forage the LMB are going to eat? The RBT is a good organism for this. It can easily double in length (8-tuple in weight) over the winter growing season and provided it isn't too big at the end of the season, can make ideal forage for 18" to 25"+ LMB.

The cool season provides these benefits.

1. Non competitive environment with existing community members. The rainbow trout are active, the BG are not. The feed goes to the trout.

2. Less predation especially with TP and BG YOY in the water. These alternatives will draw the predators because they will be easier to capture than trout in cool water. Survival over winter should be good provided they are introduced in water cool enough to slow the metabolisms of predators and alternative prey. Slower metabolism, especially for prey alternatives will provide an energetic cost advantage to the predators that they will exploit.

Were I doing this I would seek to stock 4" to 6" Trout when water temps fall below 60 degrees. I would try to grow the trout to a mean length of 10" and if it looked like they may achieve it prior to March 31st I might slow down the feed rate (natural foods may be supplying sufficient growth to complete the cycle). If you feed as much as would in the summer, you should have a great bloom going when the BG start spawning in spring and the first spawn should be very successful. You may not even need to feed the BG the rest of the year. The secondary effects of feeding should be very similar but I would mention that spring is VERY, VERY good time to have nutrients in the water and a good bloom. A good bloom will also reduce FA.

Under this scenario, all of the feed goes to grow forage for your LMB. No feed is wasted unless something other than your LMB is taking your trout (like poacher, otters, osprey, eagles, and cormorants). IMHO, you will get more benefit from feeding trout than feeding BG and I think its a viable strategy to shift feed use to the winter if the purchase of RBT isn't cost prohibitive for you.