One thing that jumps out at me is the age of the study (55 years) and the light years that the fish food industry has changed.
The age of study doesn't bother me esshup and here is why. I figure that LMB in 2023 convert GAMs pretty much the same as they did in 1968. So I am agreeable to trust it. Also, I figure that the Dry Weight percentages and energy content of GAMs hasn't changed over the same period. The study didn't make any comparisons to or use any formulated feed. I made those comparisons from recent determinations of FCR which were posted here at pond boss where the feed rate was 3% of body weight. Since I was comparing that FCR to GAM dry weight consumption at 1.6% of body weight, the comparison was very generous to formulated feed.
What was the length of those LMB? Weight was from 0.716g to 19.24g.
The LMB were small. I was concerned about this as well but the study normalized consumption on an energy basis related to the energy content of the LMB. In other words, it didn't depend on length of the LMB. Now one might "say" that length matters in terms of assimilation (efficiency of digestible energy) and respiration (metabolism) but I tested this hypothesis and here is how I did that. I calculated the annual maintenance ration ... and even though the LMB were small they required 3.65 lbs of GAM annually for maintenance. I converted this ration to BG by taken the product of the this ration with the ratio of GAMs to BG wet weight energy density. The energy density of BG is 4186 J/g while the energy density of GAMs is 5567 J/g. This means it takes (5567/4186)= 1.33 times more wet weight BG or 1.33*3.65 (4.85) or roughly 5 lbs of BG to support 1lb of LMB. This true of small LMB and if we can agree that larger LMB require ~5 lbs of BG for annual maintenance, then its very hard to argue that larger LMB use consumed energy differently than the smaller ones the study used. This is the beauty of normalizing metrics. It isolates the simplest and most elegant principles of nature.
What changes at different LMB sizes is consumption. You can't get a 1lb LMB to consume 6% of its body weight in wet weight prey everyday. They just will not consume that much. If a 1 gram LMB Fry consumes 6 % of its body weight daily in wet weight GAMs for 90 days it would grow from 1 gram to 85 grams (>7") over the same period. Some LMB are capable of this consumption but it is too rosy for most. Even for those that grow from 2" to 7" in 90 days the consumption wouldn't be a constant 6% but probably more like 9% at 2" and 3% at 7". Consumption as a proportion of weight varies among individuals where the fastest growth is obtained by the individuals that consume the most.
How does the caloric content of a gam compare to a BG? Since Gams are a very small fish (common length average is 3.9 cm) they would only fit in a narrow window of a LMB lifespan as optimal feed. (4.5" - 8.25" in length)
Sure, I wasn't saying you could feed 5 lb bass with GAMs. But I don't see why 12" LMB wouldn't consume a 2" GAM. Indeed, I have witnessed this happen. The caloric content of GAMs on a wet weight basis is 1.4 times that of BG. Swingle tested GAMs with LMB and averaged 153 lbs/acre of LMB over 1 years. Such standing weights were not achievable with BG and obviously many of the LMB that grew on GAMs exceeded 12" in length. What about 10" BG? A 10" BG weighs 1 lb. Is a 2" GAM something it would consume? Its all about availability and capability. The bio-energetic studies I have seen suggest that lower limit of consumption by piscivores is around 1/1000 the body weight of the predator. Hypothetically a 2" GAM might be consumed by a predator as large as 1760 grams. For 1lb LMB the ratio is 1/257. If adjusted for BG caloric equivalence the ratio is 1/184. Though a 2" GAM is not ideal prey for a 12" 1 lb LMB, it provides enough energy to be worth while. Five 2" GAMs are 1.94% percent the wet weight of a 1 lb LMB. Per the findings of the study, the 1lb LMB can gain on that ration only requiring 1% of wet weight for maintenance. The gross wet weight FCR at this ration is 2.4 and corresponds with a specific growth rate of 0.815 % daily. Not a lot but enough to grow a 1lb bass from 1 lb to 1.25 lbs in 4 weeks. So does it make sense for 1 lb LMB to eat 2" GAMs? Of course it does. Again it's about availability and opportunity.
Since they dried the fish to weigh them, we'd need to add water back to the fish to see how they compare to artificial feed since the LMB aren't eating dried fish.
No. Not so. The caloric content of both LMB and prey were estimated from known wet weight conversions. All of their data is represented in the metrics of bioenergetics (energy). I converted these metrics to wet and dry weights so the comparisons could be made.
