How long do the LMB maintain 1.25-2mm per day growth rate? My gut says there's a slowing in the winter and again when they are able to spawn / sexually mature.
Just to add an anecdote. I have personally observed 9" LMB grow to over 13" over the winter months (in Texas climate). They were moved from a stunted pond to a pond with no LMB. About 10 of them to a 1/4 pond. The pond they were moved to was loaded with stunted GSH. So plenty of forage. I presume most of growth occurred during the warmest part of the spans (at the ends of the period) from late September to late March/early April. So around 180 days to grow 100 mm (an average of .55 mm/day). This may be close to the maximum potential growth for length increment for ~9" LMB through the temperature profile they experienced over that 6 months. Of interest, it is unknown how old these fish were but they may have already expended most of their life potential (in years) at the time of the stocking. LMB grow throughout life and growth will be function of prey availability and the individual LMB's motivation to consume.
The motivation to consume is in part related to the length of LMB. When shorter, they will consume a higher percentage of their body weight daily than longer LMB. They are just hungrier. So a 2" LMB will consume around 15-20% of its body weight daily but a 7" LMB will not consume that much. I once worked out a maximum consumption by length curve. It suggested a maximum consumption of 3.9% of body weight daily for the 7" LMB. I worked out that function from a very basic premise. The maximum LMB weight gain in a 12 month span is 2 lbs (per Swingle) AND daily weight increment is constant (an anecdotal observation of Swingle an many others). In the paper on energetics I have referenced before, their maximum observed consumption for 7" LMB was 3.6% when feed to repletion. So the agreement isn't bad. So why do short fish want to consume more? I think the answer is built in to them to improve survival. The shorter they are ... the more likely it is that they will be eaten and so they have more growth hormone raging and are motivated to consume a larger proportion of their body weight. This helps them grow longer faster improving their chances of survival.
Boondoggle, it is certain that we over-emphasize gape when talking about optimum lengths. The part we miss is the difficulty of capture and time between successful captures during which LMB are expending energy which are thus part of the energy cost of consumption. If we assume that realized capture reflects optimum energetics, then the prey with the highest frequency of consumption is the most energetically optimum. It is not prey between 30% and 50% the length of the LMB. For fusiform prey, it is between 25 and 30% of the LMB and for BG it is between 16 and 20% the length of the LMB. Why is this important? Let say you want to supplement forage. Let's say you have 20" LMB and use 30% the length BG to feed them. You will be stocking 6" BG and I can assure you that very few of them will be eaten beyond the first day or two. This stocking will make matters worse actually because the will survive and compete with other adult BG for limited resources reducing the production of BG fry. Furthermore, they will compete with LMB for BG by eating BG < 25mm in length. Sounds good under the premise of gape to define "energetically optimum" but it will never work because LMB do not in reality consume > 30% length BG as a high proportion of their diet. Not enough of them will be consumed.
A forage pond is probably by far most affordable way to add forage. IMO the forage size should be greater than can be consumed by BG. So at least >30 mm. With this arrangement, the forage feeds only LMB. As you previously mentioned they will grow in the pond. Their length at time of consumption will depend in part on the length of the LMB that eats them but each LMB will eat a distribution of sizes where the most frequently consumed BG forage is less than 20% the length of the LMB.
We put a lot of emphasis on the first year of growth. I would not say that it is not important. For example, if the first year growth is slow, then by default so also will be the second year. But what limits growth isn't just the first year .... it is a subsequent year where the LMB reach a forage limitation. The cause of this forage limitation will always be production numbers of >30 mm BG as this number relates to the number of LMB. Each LMB needs between 400 and 500 BG for maintenance (and more for good growth).
