Greg -- you already put your finger on the professional "problem." It's easy to have relative weight, where we just look at how much a fish weighs for its length. However, growth is another matter entirely, with geographic location the key.
The idea of �relative growth� has been kicked around for years. I think the first time I heard it was from Gary Novinger, when he was a research biologist with the Missouri Department of Conservation. The idea is simple: set a benchmark and compare your growth to that benchmark. However, the hang-up has been coming up with an idea of how to get people to agree on a benchmark. After all, there are tremendous latitudinal variations in growth, partially because of the growing season length.
Wayne Hubert (Hubert 1999) took the plunge, and put a paper out there for channel catfish, with a challenge to others to expand beyond this species. Quist et al. (2003) followed with a growth standard for walleyes). They provided the percentile distributions for mean lengths at age (ages 1-10; 5th through 95 percentiles). They also provided both a combined set of means when fish are not sexed, as well as separate means for males and for females. Obviously, there is a latitudinal gradient in walleye growth, and that is part of the analysis in their paper. For this relative growth index to be accepted, I believe that states will need to come up with their own benchmarks for what is satisfactory growth in their geographic locations. For example, Kansas walleye populations were near the 90th percentile in many growth assessments. In contrast, northern Manitoba populations may be growing at a satisfactory rate when they are at the 20th percentile level. Do you see my point? As long as people accept the standards in Quist et al. (2003) as our distribution-wide benchmark, then biologists can set their own values for their location.
Recently, Jackson and Hurley (2005) provided a growth summary for black and white crappies so relative growth could be assessed.
So, those are the only species for which there are range-wide standards are available. However, Mike Quist and his graduate student are close to finishing up standards for a bunch of other standards.
Hubert, W.A. 1999. Standards for assessment of age and growth data for channel catfish. Journal of Freshwater Ecology 14:313-326.
Jackson, J.J., and K.L. Hurley. 2005. Relative growth of white crappie and black crappie in the United States. Journal of Freshwater Ecology 20:461-467.
Quist, M.C., C.S.Guy, R.D. Schultz, and J.L. Stephen. 2003. Latitudinal comparisons of walleye growth in North America and factors influencing growth of walleyes in Kansas reservoirs. North American Journal of Fisheries Management 23:677-692.
