Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Where did RW come from ?

Snipe's use of "average" and Sunil's use of "statistical" are a pretty good description of what standard weight is. Sunil's remark about only 2 factors (Length and Weight) is spot on. RW is just a metric that quantifies how a particular fish relates to the statistics of a particular data set. Anyways, if you were to collect information from many samples and then plotted the weight with respect to the length, you would get a scatter of points that trends higher in an obvious curved fashion. A power function fits those points best (SW = a * Length^b). That function is Standard Weight. If the plotted on log-log paper you would get a scatter of points that trend higher in linear fashion that is best fit by straight line. That log function takes the form (SW=10^(log10(a) + b*log10(length). Either equation produces identical estimates of the standard.

Lets say you divide the data into segments of length ranges. Let's say you are now looking at the range of lengths from 12.75" to 13.25". You calculate the RW for each and every fish in the group and then make a frequency plot for RW ranges. You should find that the highest frequency of occurs around RW 100 (lets say the range 95-105). The form of the frequency plot will be akin to a bell curve. Higher RW are less frequent and so are Lower RW less frequent. When your fish exceeds RW 100 then you should be able to say it is in better condition that 50% of similar length samples of the SW data set. Fish that are >140 RW are very infrequent in the sample data. When you have a sample that exceeds 140 RW it may be in better condition than 98% or more of the data set's fish of similar length fish.

But these are not the odds in your pond. If you have one sample at 140 RW then you will likely find other samples near that RW where some will be higher and others lower. In fact, it very well could be that none of your fish are less than 100RW in defiance of the standard weight sample set. RW is just a refection of the consumption that exceeded what was required by 100 RW fish. In fact it is simple to calculate. A 140 RW fish consumed 40% more in the past 12 months than a 100 RW fish consumed. It just ate more, that's all. A high average RW in a pond is an indication that food is abundant and that fish are able to store energy above the standard at their respective lengths. Because RW is primarily a function of food availability, it is not primarily anything genetic. Period.

You will probably find that high RW favors shorter fish. They often weigh less than longer fish of lower RW. This much is certain. The heavier fish consumed more. But lets consider a shorter fatter LMB and longer leaner LMB of the same weight. According to energetics, each consumed the same weight of forage. Keep in mind that a fish only has 1 mouth. Each fish has similar opportunities for encounters. All that may be different is that one is 1" longer (or shorter) than the other. The same weight on a shorter fish yields a higher RW.


A person should not read too much into areas, regional strains, etc. The standard weight curve is nothing but what it is. The most probable/frequent weight function fitted to a large dataset. Don't overcomplicate it. Use RW as means to understand trends. If your RW is higher than 100, then conditions in your pond are more favorable than the waters of the standard weight data set (that's a positive). If you notice reductions of RW, then forage additions or culling could benefit your fish and turn the tide.

With regard to region, LMB in TX require more forage than LMB in KS to grow to the same arbitrary length and weight. What is different in the South is the production of forage. It starts sooner and occurs more in a forage production growing season. TX LMB in favorable waters have more forage to eat. Something that is a good thing because TX LMB will expend more energy for maintenance than KS LMB of the same weight. This is according to energetics. Higher temperatures increase metabolism and the amount of forage that LMB need to support it.

So if in KS, if what is limiting your RW is the amount of excess forage your LMB are eating. You have three choices to improve RW. Reduce competition, increase the forage, or a combination of these two approaches. One thing is certain, it will not take as much forage consumption in KS to do the same thing. Less of the energy of forage consumed will go towards maintenance in KS and more of energy will go toward gain.

IMHO, northern waters can produce better growth than we are accustomed to but it would require some form of supplemental feeding. One needs a means to override the typical lower production of forage to accomplish greater growth. There is a lot to learn in this area. We don't yet understand how much additional forage LMB in northern waters would consume if supplemented. Right now an ongoing case study by Solitude Lake Management in a high density LMB Female only pond is providing clues. In trying to understand climate, I used Ronoke, VA. If Ronoke, VA is comparable to the climate where the pond is located, then this it located in a colder place than say Wichita, KS. They have grown Northern strain LMB to astonishing RW and Weights in only 3 years. Here are a few bullets of what they have accomplished thus far.

* Annual increase in average RW in each subsequent year
* Growth from an average weight of 1.5 lbs to an average of 6.7 lbs in three years
* An average of RW 145 in year 3
* A max RW of 165 in year 3
* A max weight of 9.25 in year 3.

The stocked females were 1 to 2 years of age at the time of stocking. There could have possibly been some 3 year old fish but these would have to be considered slow growers. Even so, even the growth of the slower growers isn't shabby.