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8 7 .... . . . . ~ 6 . - CI).J::. 5 - - .. . ~ l: . . 0 4 . .J::.e .. ~ . i- 3 . .... E e 2 . . . . C) e 1 - . .. o , , I 150 250 350 450 550 Bonytail Total Length (mm) Figure 7. Growth rates ofbonytail (n=31) captured from Cibola High Levee Pond for the period of record (1993-2004). Data represent fish recaptured between 9 to 24 months after initial contact. Data were grouped into 50-mm size categories and the curve was smoothed using a rolling 3 category average (Figure 8). Growth is typically the most rapid during early life, but interestingly for this community it appeared to peak for the 300-mm size group. Smaller-sized bonytail (<200 mm) exhibited a slightly smaller growth rate of3.5 mm/month, compared to medium-sized (300-400 mm) chub. Growth sharply declined as fish aged and grew in size. Growth for 370 mm bonytail dropped below that measured for smaller fish, and the decline accelerated once fish reach 400 mm. The retarded growth in the smaller cohort was not expected and would generally not be considered normal for any fish species. In this case, it is quite possible it may represent an artifact of small sample size, measuring error, or possibly marking stress on smaller fish. It is equally possible it reflects differences in growth due to dietary competition among smaH fish and a change in diet of larger fish. Bonytail are extremely prolific, producing tens of thousands of young annually. Quite possibly, competition for plankton by chub may be aggravated by their high number and by direct competition from the 1,000 adult razorback sucker that share a similar diet. When larger bonytail shift their diet toward larger invertebrates and small fish, there may be a greater abundance of food which in turn improves growth rates. We plan to examine the diet of smaller (<200 mm) bonytail more closely this year: The largest bonytail were females; several exceeded 500 mm while all males were under 490 mm. There was insufficient data to compare growth rates for both male and females but we suspect that growth for mature females is either accelerated or continued compared to that of mature males. For example, the sex ratio of 350-mm bonytail was l: 1; however, that ratio declined as fish size increased to a point where all fish over 500 mm were females (Figure 9). 6