Pond Boss Forums MANAGING AN EXISTING POND Corrective stocking F1 Tiger Bass Not Growing As Expected

Jason, a few days ago when reading archives here, I noticed a post by Dr Dave Willis with regard to RW. He said the RW tables are based on 75th percentile fish. So the standard weight is not the average of the samples of a given length class. It is well above the average. To grow at maximum rates, fish will most often have RW well above 100. But isn't necessarily always the case. Some outliers gain weight just as fast but do so on a longer frame.

LMB are not gluttonous, but they grow pretty fast when forage is abundant. They don't waste forage but rather use it as efficiently as they can within the limits of their individual growth. There is a limit to how fast they will grow and on any given day it depends largely on the temperature and whether they were able to consume enough to fuel that individual maximum growth. High RW LMB are consuming often enough that their blood metabolites remain above some minimal level that allows excess consumption to be stored for later. Fish with lower RW feed less frequently enough that are either unable to store the additional energy or possibly have had to rely on the stores they previously packed away.

When studying conversion of fish in LMB, I came across some weird stuff. It was remarkable how well LMB convert fish and it seemed possible that LMB could make gains in excess of what they could if growing on forage if they were fed a feed comprised solely of fish meal and fish lipid. Just to give you an example. Over a grow out period of 120 days, a 1 lb LMB consuming 1.5% of its body weight of a feed comprised sole of the dry components of Gambusia would gain from 1 lb to over 25 lbs. This of course isn't possible. We know it won't grow long enough to weigh 25 lbs. So the obvious understanding that arises from this exercise is that the premise is false. LMB either will not feed continuously at 1.5% daily on dry GAM AND/OR if they will, they will only metabolize what they need to fuel their individual potential for growth. So here is what I decided. I decided the later is the most plausible and that a big 1.5% meal of dry GAM would probably delay its feeding response for a considerable time.

In optimum forage theory, we assume that consumers adopt behaviors that optimize efficiency. If this is true, then LMB should consume no more than they need to grow at their individual potential. In thinking about this, trying to work out all the potential pitfalls and holes, here is how I decided to understand LMB foraging behavior.

An LMB's internal growth mechanism tries to maintain its blood metabolites within a range of levels. There is threshold below which an LMB will be stimulated to forage. After consuming prey, it may continue to forage if the prey was small ... but once it has consumed enough prey to bring its blood metabolites above that minimum level it will terminate foraging to handle its consumption. It is during handling that most of the digestion occurs. There seems to be a limit as to time rate of metabolization. IOWs this seems to be limited by the metabolization of foods required to fuel the LMBs individual potential for growth. If more is consumed than can be metabolized before evacuation, then some of the energy will be unused and exit in the fecal matter. If this is so, optimal foraging theory suggests that LMB will adopt behavior that will reduce this waste.

Now, after this background, on to what I think your question was. I think there is another minimum threshold for blood metabolites that lies below the threshold for foraging. This threshold is the lowest level of blood metabolites needed for metabolism (including foraging activities). As this level is approached, the LMB will access the energy stores of its own body and use them to fuel foraging activity and other basic metabolic function. The LMB loses mass when it does this. In fish that grow at maximum potential, this happens infrequently, but when consumption falls below what is required for maximum potential growth, an LMB may be from time to time accessing its body mass for energy and would most certainly have less excess consumption to store on its frame.

To Eric's point of spawning, there are two potential ways fish lose weight (thus RW). One is the loss of gametes expelled in spawning. The second is the loss of body mass to fuel metabolism during a period of lower consumption. The potential of loss over a period of 2 weeks when abstaining from consumption may surprise you. For the past 2 weeks ... in your climate ... the daily consumption of BG to fuel metabolism is ~1.3% of body weight daily. So if they haven't been eating due to spawning activities, then they could lose that same percent of bodyweight each day of abstinence (given Kitchell found the energy density of LMB and BG are the same). Over 14 days that is ~ 17% of body weight. That alone would take a 115 RW LMB to 95 in 14 days even if the gametes had not yet been expelled. Fish will recover from the rigors of spawning but if they are not in sufficient condition they may either not spawn or be weakened so as to die from the activity.

One last note. How often fish are consuming prey depends on density of the prey. In the spring, consumable prey is at a minimum and could be below the thresholds needed to fuel maximum growth. The greater the numbers, the greater the frequency of opportunities. Also, the relative ease with which varying sized prey can be successfully captured is important to the frequency of consumption. The right balance of numbers, encounters, and successful attempts is what leads to the potential for maximum consumption and thus maximized growth.