Pond Boss Forums MANAGING AN EXISTING POND Feeding Feed trial experiment

I will respectfully disagree. Sorry but we have to have the freedom to disagree.

The truth is that the assumptions (Swingle's theory and widely held wet weight conversion) very nearly predicted the outcome of the first 10 days. Even Snipe will tell you that assumptions demonstrated predictive ability. To be sure, Snipe isn't saying that the feed converted at 1.47ish in the absence of pond organisms. In fact there must have been a very substantial proportion of consumption attributable to pond organisms and he explained the results in that very way. Snipe isn't new to this and he would not lead us to think that feed converted all on its own at 1.47ish. Snipe told me that the best he had seen with YP that were feed-trained before the testing was about 2.2 to 1. He said that it was in clean water tanks without the normal eco system present but feed rates were much higher than 3%, like 7-8%, with Optimal Jr.

You want to see something really cool?

Let's try to predict the FCR of Snipe's YP at an 8% feed rate using what was realized in first 10 days of this trial using optimal. As a starting place lets assume 0.667 % maintenance solve for the intrinsic FCR. Below this is displayed in the spreadsheet where an FCR of 2.158 is the solution intrinsic conversion (Intrinsic FCR) above maintenance that is consistent with 0.667% maintenance and the growth of Snipe's BG fed Optimal feed with a GROSS FCR of 2.85. These assumptions if true would grow the BG to the weight Snipe observed.



Of course true intrinsic FCR depends on the true intrinsic maintenance rate because they are variables of the function that models the observed growth. You see, assuming different values of SMR (specific maintenance rate) makes you solve for different values of intrinsic FCR. True values can only be obtained by feeding over different periods different rates of feed. Only by doing this can the values of maintenance of intrinsic FCR be obtained. These properties, intrinsic to the feed/species combination, are true only if they are the same at any reasonable SFR (specific feeding rate). SFR is merely the proportion of fish weight that is fed every day and so clearly there is a limit how high that can be. For example fish can't eat two times there weight in feed. Ideally to solve for these intrinsic properties we constrain the solution to a feed/species combination. That said, lets firmly press our tongues to cheek and just see how closely we can predict the FCR of Snipe's YP at an 8% feed rate.




So starting with Swingle's principles, an assumption of 0.667% maintenance rate, and the first 10 days growth of Snipe's BG we predict that at 8% of body weight daily that Optimal feed has a GROSS FCR of 2.35. To be sure, this is not exact. Not that far off from Snipe's best of 2.2 with YP but not exact. Far off is going from an FCR of 2.85 in the first 10 days to an FCR of 1.42 in the following 30. Like Snipe said, that doesn't make sense unless the fish ate something other than feed in the latter part of trial. So if you don't bat an eye at the FCR going from 2.85 to 1.42 during the trial than you should be absolutely astonished that we could predict an FCR within .15 using the assumption of 0.667 maintenance and the principles Swingle left us. "A fish must consume maintenance to maintain its weight ... it may convert consumption above the maintenance into growth". Eloquent and it fits what scientist call a physical law. It can be expressed as an equation and it can be tested against evidence.

We failed by 0.15 to predict the FCR of Snipe's YP. This may be because YP convert differently than BG. Or because the assumption of 0.667% for maintenance is wrong. But for now, lets assume YP convert Optimal equivalently and that we need to adjust the maintenance so that the maintenance and intrinsic FCR are equal for both treatments. I got very lucky and with a single guess for maintenance at 0.8% I found the Intrinsic FCR to be 2.019 where at an 8% feed rate the FCR is 2.24.




Now that is down right close ... still I would much rather do that with the same species than mixing and matching BG and YP. Anyways, it tells us that it takes a little less than 1% of a fish's body weight of Optimal to maintain its weight. It also tells us that Optimal converts "somewhere around 2" (give or take a little) for the feed fed above maintenance. This means that in a pond, for fish that are growing anyway, the direct conversion of the feed is ~ 2 to 1. There is an additional manuring effect where the fish manure from eating the feed further stimulates the food chain providing additional natural foods. To imagine this effect think of third world countries where producers very effectively grow fish soley by stimulating the food chain with animal excrement. Yes when you feed your fish ... you are adding animal excrement to your pond ... it is just that the fish are eating the feed first. This is how FCRs can be below 2 in pond settings. Pond foods provide the maintenance and a proportion of the growth. The feed is converted at the optimum rate and receives credit for all maintenance and growth.

Another thing. Don't be persuaded that Optimal outperforms Purina from the results of this experiment. As Snipe mentioned, the reason for such low FCR is that the fish were eating supplemental pond organisms. Because of this we can derive no valid conclusions about the intrinsic properties of the feed (maintenance and intrinsic FCR are those properties). Except, perhaps in the early going when Purina outperformed. The conversion made then implies strongly that the food the fish were eating was limited to feed. Based on that alone, I lean to Purina though by my calculation the FCRs are comparable. Because pond organisms played such a large role ... I would lean that the Optimal cage occupied better real estate which had the effect of providing the BG more pond organisms to eat.

But back to conversion of feed being 4 to 8 times more efficient. This isn't supported by real world conversions of feed to fish flesh. The analysis above using 70+ year old principles leaves no doubt that it simply can't be the case. This is because the acquisition of food is evidently only a small proportion of the metabolic consumption each day and it probably can be ignored. In other words, an easy meal doesn't actually add all that much. Furthermore, comparisons of efficiency are only valid when the dry weight consumptions are equivalent. There are lots of ways to twist facts into something that is not true at all. What I love about Swingle's principles of maintenance and growth is that they form a natural law that has proven to be fundamental to the energy budget of fish maintenance and growth. The variables of the function (FCR and SFR) represent intrinsic properties of a feed/species combination. This is what makes science beautiful to me. It removes the anecdotal mumbo jumbo of three bug eyed BG grown on three different feeds and it instructs you not put that in your mouth and swallow. Science uses simple principles that have mathematical relationships such that theory becomes testable in the real world and a highly sharp tool for control and planning that have real world application to the economics of growing fish. Science weeds out false claims and it creates a firm platform by which to expand knowledge. But for sure ... some will say Optimal converts at 1.42 referencing this anecdote even after Snipe warned us that this isn't the case because the fish ate supplemental pond organisms in addition to the feed. And that saddens me because its just an example of picking what one wants to believe (or for some what they want to sell) as opposed to getting to the fundamental knowledge of the feed/species combination. The former is BS while the latter is something you can apply in the real world as so many fish producers already do.