Pond Boss Forums INTRO Questions & Observations Rate of digestion relative to temperature.

I found this on page 127 of "Bluegills, Biology and Behavior", by Stephen Spotte.

This is from a study conducted during the summer, which produced results showing that the half-life of stomach fullness decreased linearly over a given temperature range...which in this case was 10-25 degrees Celsius (50F-77F).

An equation was used to demonstrate this regression:

y = 23.1-0.901x

Where y is the half-life of stomach fullness ( brought upon by digestion), and x is the water temperature in Celsius.

If we plug in their numbers, we see that at 25*C, (77*F), the elapsed time needed was only .87 hrs. However, at the other end of the scale, 10*C (50*F), the time needed increased to just over 14 hrs.

The regression is reportedly linear throughout the temps recorded during the study, but I haven't found any further information to indicate if it remains so as water temps continue to decline. However I am reasonably confident that at minimum, the time needed for digestion will continue to increase as water temps fall. If we allow for a temp. of 38*F, the time increases to over 20 hours, IF the rate continues to be linear.

This shows that time required for digestion is dependent upon temperature....the colder the water, the longer the time needed. What bearing, if any, the addition of pelleted, processed feed might have on the digestion rate is unclear to me, as are any possible ill effects that might be suffered by the fish as a result of undigested feed remaining in the stomach, vs. natural forage.

The author referenced a handful of studies in this regard, some of which are 40+ years old and may not reflect current thinking and understanding. Nevertheless, I am trying to locate these pieces to order to try and further my understanding regarding feeding processed pellets during the winter months.

Good post Tony.

More digging has resulted in a suggestion of three primary variables influencing rate of digestion: temperature, weight of food portion in the stomach, and fish weight.

It has also been suggested that duration of digestion may depend greatly on food composition and quality. This begs the question as to whether high protein feeds take longer to digest in cold temps, when compared to natural forage.

"Duration of Gastric Digestion in Fishes", V.B. Tseitlin

This is really good stuff! So let me ask this. I feed a 45% protein fish meal based pellet. Does anybody know the exchange rate between natural forage and pellets? What I mean is, if I feed 1 ounce of 45% pellets,, about how many ounces of natural forage, such as FHM or BG, are required to be equivalent?

Edit: Sorry, for clarity, I mean from a fish growth standpoint. We read everywhere 10 lbs of forage for one pound of growth. I assume that 10lbs is natural forage. How many pounds of high protein pellets to get that 1 pound of growth? Keeping in mind pellets are relatively easy for even my dumb cc to catch so it is not exactly a fair comparison to when fish are expending energy to catch the natural forage.

Bill, My simple mind wonders how much of the "10 pounds of forage" is water and any other non-digestible or other matter that is unable to be utilized. With processed, "high digestibility" feeds, LMB convert at about a 4:1 ratio. My SWAG is that only about 4 pounds of "natural" forage is digested...

Another factor that could play a huge part in weight gain is the amount of calories expended hunting natural forage. Chasing 300 (~1#) adult fatheads will burn FAR more calories than gulping down a 1# trout (arguably the ideal bass forage fish)

I heard that it's a two to one, two pounds of feed makes one pound of fish.



Pat W


All I know is that my fish reall look fat and growing fast when I started feeding

Pat, a lot depends on species and also the feed, but I am pretty sure for Northern Black bass, quality fish food is converted at close to the 4:1 ratio. Tilapia get around 1.2:1...Catfish and bluegill around 3:1

Rainman
Even those rates are far better than the 10-1 for forage fish conversion. What's also good is the benefits that the predators get by eating whatever just ate the feed. Win win


Pat W

Now correct me if I am wrong here but I would expect the 10-1 ratio is the ratio of true cellular material to water in natural feed. % of oils and protein would depend on the feed fish.

I would expect there is at least 10% water in pellets too. Maybe even 20%.

Cheers Don.

Anyone else remember the story told by Bob Lusk about meeting with... (was it Griffin?) concerning the largemouth feed being developed?

Where the fellow opens the drawer and pulls out a dog turd looking little thing, and announces that this is the nutritional equivalent of a trout?

Maybe I'm thinking of something else.

I see PBM did an article in the Jan/Feb 1996 issue on "supplemental feeding in the off season" if anybody has a copy.

Sparky, I don't recall that particular story. I know Dr Griffin was attempting to make a feed equivalent to trout. I also recall hearing some feed manufacturing company claiming they had created the equal(Cargill?), but fish refused to eat it...

While researching, I'm discovering what Rainman already knows and is patiently attempting to explain in another thread currently exploring this subject. That being that undigested food may be expelled without contributing much by way of growth to the fish. I THINK this is encouraging, as it may imply that the processed feed is purged, rather than just laying in the stomach, undigested.

On the other hand, this MAY also support the hypothesis that winter feeding provides very little benefit to certain species of fish, most notably warm water species. Even if they are willing to feed, cold water inhibits or at least depresses digestion, and undigested feed is simply expelled.

This tidbit also came from "Bluegills, Biology and Behavior", by Stephen Spotte.

I have found that my fish quit feeding on pellets at a higher temp than those up North.

With all of this recent talk regarding Koi, and Garden Web, I thought I would nose around and see what's going on in the ornamental fish world. As is often the case, it's difficult to find information that you feel comfortable trusting. So keep that in mind as you are reading through these links....and most importantly as far as I'm concerned, remember that Koi are not bluegills...what may be applicable for one, doesn't automatically translate well for the other.

Some professional info...4 links under the banner "technical information". Written by a very familiar, and extremely knowledgeable person:
http://www.mazuri.com/koi.aspx?gclid=CIiD64KFyMICFQwyaQodsWIA3Q

The claim is made here: http://www.thekoikeepers.com/feeding/feeding.html that Koi do not possess a true stomach, rather digestion takes place in the long "gut" (intestine?). If true, maybe this explains a thing or two?

This link extolls the virtues of feeding Koi a product high in wheat germ in preparation for winter, in order to help clean out the digestive tract. They also claim once water temps fall below 50*, any food remaining in the fish may begin to spoil.
http://www.koi-fish.com/koi-care/feeding.html

I'm not trying to prove or disprove anything by posting these links, especially regarding our pond fish which appear to be quite different from Koi, in a digestive manner of speaking. Just seeing what all the commotion is about.

I don't know how accurate this info may, or may not be. The question of whether anything relevant can be extrapolated from these links, goes unanswered by me.

This is all very interesting stuff.

I wonder how much this relates to beneficial bacteria in the stomach/gut of the fish? Depending on the water type, genetics, food sources, climate, etc. I wonder if the same species of fish in different ponds may possess quite different flora in their digestive tract to help them absorb a particular diet under certain conditions?

What may be present in southern ponds, may not thrive in northern ponds, which may explain some differences in eating patterns. Since fish are so good at moderating their internal PH and such vs the water they are in, who is to say they cannot somewhat influence the chemistry of their innards to favor a type of flora to digest a food source available to them? It may take them time to adjust this, and thus fast temperature swings and water chemistry cause a drop in appetite as they are playing catch-up internally?

Just thinking out loud, but I think a lot is misunderstood about the role of beneficial bacteria in most animal's guts and how it interacts with health.

My perch would love to eat right up to ice over, maybe even after. I stop at 50 degrees, but they are quite active even under the ice. I always thought they floated around like logs until I got my underwater camera down there and took a look. They were clearly actively hunting for food and curious about the camera.

It also may go along with N8tly's comments in the other thread about there not being a good commercially available feed for winter feeding yet. Maybe the natural food the fish catch digests just fine in cold water, but the artificial food is not of the best composition for cold water digestion. He implied that if a commercial food does come out for cold water feeding, its composition will be considerably different than current feeds.

We had a program at the PB conv (Fish nutrition)0n this topic. It is metabolism (bioenergetics theory). I will add some threads.


http://forums.pondboss.com/ubbthreads.ph...true#Post126584


Bioenergetic models estimated that the largemouth bass population in these ponds consumed between 132 and 171 kg ha (roughly 150 lbs per acre) of bluegills in the first 300 days after stocking to maintain the observed growth.

Each population of largemouth bass was predicted to have consumed 4.2 to 6.7 times their own biomass in bluegills in 300 days to maintain these growth rates and biomass.


Recent research has revealed consumption-dependent error in many bioenergetic models, including the one used in this study, which was particularly large when growth rates were fast . Thus, the percent of maximum consumption by largemouth bass estimated in this study were likely underestimated which probably indicates that the bluegill densities in the ponds used in this study may not be great enough to meet predator demand in the future, leading to slower growth, poorer condition, and a possibly lower production of trophy-sized fish.


A little confusion on the BG size. The catch rate BG were 5 inch average while the stock size (150% of normal in the study or the recommended 2000 at the convention) were small BG as were the LMB when stocked.


In this study LMB numbers were low and survival to age 1 was below normal. Even at those reduced rates the LMB were most likely to have over eaten the BG forage base which was 150% of normal if the study would have gone beyond 1 year.


http://forums.pondboss.com/ubbthreads.ph...true#Post175828


http://forums.pondboss.com/ubbthreads.ph...true#Post259185

North American Journal of Aquaculture
Volume 65, Issue 2, 2003

Evaluation of Practical Bluegill Diets with Varying Protein and Energy Level

DOI:
10.1577/1548-8454(2003)65<147:EOPBDW>2.0.CO;2
Richard H. Hoagland IIIa, D. Allen Davisa, Nguyen Anh Tuana & William J. McGrawa
pages 147-150

No problems related to water quality or disease were encountered during the experiment. As indicated by their high survival (>98%), the fish were able to tolerate repeated handling and weighing. The performance of the fish under laboratory conditions is summarized in Table 2. Fish maintained on a diet containing 44% protein and 8% lipid (designated as D44/8; other diets designated analogously) exhibited significantly higher final weight (12.99 versus 9.36–10.70 g) and weight gain (643.9% versus 429.7–507.3%) than fish maintained on diets containing lower levels of protein. Fish given D44/8 also had significantly higher feed efficiency (77.9%) than those on diets with lower levels of protein (60.6–66.7%). Total feed offered was significantly higher for fish maintained on D44/8 (14.4 g) and D44/12 (14.2 g) than for those on D32/10 (12.6 g) and D32/6 (12.5 g), with the remaining diets being intermediate. No significant differences or notable trends in the protein conversion efficiency values among fish given the various diets were found. Proximate analyses for dry matter, protein, and lipid in whole-body samples were similar among all but one of the treatments. The single exception was the proportion of dry matter in fish maintained on D32/10, which was higher than that in fish from all other treatments.



From Fish Nutrition



• The immense variety of cultured finfish species hampers efforts to simplify production industry wide. Approximately 170 taxa are currently cultured, including carnivores, herbivores, planktivores, and omnivores, each posing its own set of nutritional demands .
• Fish meal has proven to be an excellent dietary protein source for finfish, leading to its description as an ‘‘ideal protein.’’ The ideal protein concept is based on the premise that if the amino acid profile of the feed mimics the whole-body amino acid profile of the animal being fed, protein utilization and growth should be maximized
• Lipids, fatty acids, and their derivatives play a role in virtually every physiological process that occurs and for this reason dietary lipid composition and content represent a massive sector of overall nutrition. Nowhere is this more true than in finfish nutrition where lipid can exceed protein in the body composition of finfish, a testament to the physiological and energetic importance of this nutrient class (Tocher2003). Aside from physiological importance, lipids are indispensable energy sources, especially for finfish, which are not well-adapted to carbohydrate utilization.
• Dietary protein and energy must be kept in proper balance because a deficiency or excess of dietary energy can reduce growth rates. Fish fed diets deficient in energy will metabolize more expensive dietary protein to meet energy requirements. Excess dietary energy can decrease protein intake and suppress growth.
• finfish do not require carbohydrates in their diet, … complex carbohydrates cannot be digested and utilized efficiently by most finfish species. A general dichotomy exists in the carbohydrate digestive ability of warmwater omnivores and herbivores versus the inability of coolwater and coldwater carnivores, which lack the appropriate function necessary for digestion of carbohydrates.
• For this reason, diets fed to these fish rarely contain more than 20% complex carbohydrate
• Conversely, warmwater omnivores or herbivores (e.g., channel catfish, tilapia, common carp, and white sturgeon) adapt well to diets containing as much as 40% dietary carbohydrate .
• Although vitamins and minerals are required in minute amounts compared with protein, lipid, and so forth, they are critically important, … Every micronutrient has a deficiency disease associated with it, the effects of which are sometimes irreversible or fatal. For a few vitamins and most minerals, excess can be equally detrimental, resulting in toxicity.

• Because fish growth often is limited by food availability, supplemental feeding is a logical tool to improve the condition of fish in small impoundments as the energy cost for bluegill to feed on pellets is small relative to the high caloric intake, which can be 4-5 times greater than those fed natural foods (Schalles and Wissing 1976).
• Substantial increases in the standing stock of bluegill in ponds that receive pellet feed have been recorded (Schmittou 1969) and, in lakes, pellet feeding has been found to increase the number of large bluegills (Nail and Powell 1975).
• These results indicate that total fish production and production of bluegill were each increased approximately 75 to 80% by supplemental feeding in 19 months after stocking (Schmittou 1967)

• Previous studies demonstrated that feed in excess of 10 pounds per acre per day in bluegill ponds was not utilized. Some accumulated and decomposed, thus depleting the supply of dissolved oxygen which resulted in fish kills (Schmittou 1967) .
• the rate of growth of sunfish can be increased by short-circuiting the food cycle, thereby producing harvestable size sunfish in a shorter period of time than would occur under natural conditions (Carnes 1966).
• The pellet size should be approximately 20-30% of the size of the fish species mouth gape. Feeding too small a pellet results in inefficient feeding because more energy is used in finding and eating more pellets. Conversely, pellets that are too large will depress feeding and, in the extreme, cause choking. Select the largest sized feed the fish will actively eat.
• Addition of supplemental pelleted feed did not contribute to the rate of growth of young shad, but did increase the growth and spawning frequency of adults.

Ewest, thank you for taking the time to contribute to this thread. I should probably admit however, that trying to absorb and comprehend all of that great info will take me a LONG time, IF I am even up to the task in the first place.

I don't like to pull bits from here, and pieces from there, and then try to assemble them into some semblance of coherency. I think it's too easy to lose vital, supporting information about the whole picture if one is simply grabbing pieces of the puzzle and jamming them together haphazardly, in an effort to make the picture into what they think it should look like. Your efforts to showcase the entire picture are always appreciated.

Understanding that, are you aware of any studies or trials concentrating on the pros and cons of feeding processed, high protein pelleted feed to bluegills during cold water periods?

Sparkplug........thank you for this very informative thread. I've recently (since August) been feeding a mix of GFC and Cargill 4512 through an automatic feeder. The larger feed floats and the smaller feed sinks. I mixed the (2) feeds after a conversation with Todd Overton. Todd didn't suggest that I mix them, but indicated it would not hurt to do so and would be interesting to see what became of it. The fish have been feeding religiously (on the surface). The feeder ran out of feed this week. As the winter months are upon us, I've been indecisive as to whether I would re-fill the feeder immediately or not for my (CNBG & RES)forage base. I surely don't want to keep dumping feed into the water if they are not going to feed. Also, I don't want to feed if the fish can't utilize the nutrients, so here I am. SE Texas winters are not too harsh. The pond has several underground springs feeding it and always seems to have fog on the water on cold mornings. I'm not sure if (and when) the temperature will get low enough (sub 50) and stay there. Any suggestions or further info will be most appreciated.
Charlie

Thanks for the kind words Charlie, but at this point I'm not sure if informative is the adjective best suited to describe this topic. Ruffled feathers was not the outcome I had hoped for.

Maybe someone from the Texas assemblage can share what has worked for them in winters' past? As for me, in my location, I'm not going to feed. There just appears to be more 'cons' than 'pros', even if the possibility of harming my fish is removed from the picture.

I'm still digging though.

Sparkplg

Ruffled feathers can be smoothed out over time. You can't make an omelette without breaking a few eggs! I am still feeding just once a day now and the CNBG are going at it fairly well cause the weather has been mild. Keep up the good work as everybody will be the better for it

Pat W

Sparkplug...I hope you continue asking those questions to make everyone think and reflect. That's what learning is all about...
Charlie

Great thread. If the water temperature is 45F or above and the fish regardless of the species are willing to eat floating pellets then giving the fish some or a reduced amount of food would IMO be okay. This does at least two things. 1. It keeps the fish better habituated to pellet food. 2. I keeps the fish eating and maintaining their weight or even gaining some weight. A fish that stops actively feeding below 50F has to rely on body fat for nutrition which often means using some body biomass for energy and life processes(see below). Reduced feeding does usually occur in many species during winter water temps of 39-45F depending on water temps. In many ponds with fish biomass at near or above carrying capacity natural foods are usually limited numbers (density) due to the large number of grazers (consumers). Most all ponds that receive fish pellets have fish biomass above normal carrying capacity which means high inter and intra competition. Thus not a lot of natural foods are readily available during the cold water months when fish are crowded. Vulnerable prey items quickly disappear.

When I researched winter fish behavior during cold water temperatures under ice cover for overwintering fish in cages, one reference noted that fish do not need to actively feed or do not need to feed during winter months to stay alive. The reference noted that many fish in 39F water do not have to feed and can absorb enough minerals from the surrounding water to stay alive and healthy until water warms in spring. This assumes dissolved oxygen remains adequate for fish survival.

Several studies have noted that non-feeding fish in winter will loose weight after utilizing fat reserves. Some fish will even utilize body protein for energy production when fat reserves are depleted. When the fish resumes feeding all lost body mass has to be replaced before weight is added to the fish's body condition (weight and growth) prior to when feeding stopped. Anything that the fish can 'safely' eat during cold water conditions will allow more top end growth before it dies. As noted during cold water temperatures, some types of pellet foods might be detrimental to some fish species depending on the fish species and the water temperature.

Thanks, Bill... I did have a concern that the fish would have to "re-train" themselves to pellet feed this spring. Also, I can see where fish, in a new pond (like mine), would not have as much natural forage to winterover on than if the pond was more developed. Another concern was if the food pellets (that I already have) would go stale, dry out, or would go bad (spoil or mildew) in sealed 5 gal buckets. This is my first winter in my first year pond. With all that said, I believe I will continue to feed. I see no value in having to put weight back on the fish this spring when I can just maintain, if not increase their weight this. Winter.
Charlie