AN EVALUATION OF ALTERNATIVE FEEDNG METHODS FOR THE FATHEAD MINNOW (PIMEPHALES PROMELAS) IN AN EARLY LIFE STAGE TEST

Abstract

Several levels of brine shrimp (Artemia sauna), or brine shrimp plus a commercially prepared supplement, were evaluated according to their ability to support the survival and growth of the fathead minnow (Pimephales promelas) in two 32-day Early Life Stage (ELS) tests. The tests were conducted according to a U.S. Environmental Protection Agency (EPA) protocol that recommended a minimum control wet weight of 100 mg (Lemke 1983). The 100 mg minimum weight was achieved with the highest level of brine shrimp alone in Test I, and in Test II, the middle and highest levels of brine shrimp only, and the mid-level plus supplement. The time weighted averages (T.W.A.) of brine shrimp/fish/feeding for treatments achieving the 100 mg weight were: Test I - 314; Test II - 293, 557, 263 + 0.40 mg supplement, respectively. The growth (weight and length) of fathead minnows given various food materials to supplement the brine shrimp nauplii was not statistically different from the growth of the fathead minnows given equivalent amounts of brine shrimp nauplii alone in Test I. However, in Test II, weight only was significantly lower for the minnows fed brine shrimp plus the supplement than for the minnows fed brine shrimp alone. Furthermore, there was no significant difference in the growth of the minnows between any of the groups of supplements used in Test I. An additional tank was included in Test II to observe if overall growth was affected by fish density by starting the test with 25 rather than 35 embryos at the same food level. The lowest level of brine shrimp only was used in the comparison, and the final weights did not indicate any difference between the two treatments. The highest level of brine shrimp only in Test I, and the mid-level of brine shrimp only in Test II received nearly identical food amounts with similar results in weight gain. Both tests indicated that a plateau had not been reached for maximum growth when fed brine shrimp alone. However, further increases are not advised due to observed fouling of the water at the highest level fed in Test II. Although the highest level of brine shrimp only in Test II produced the greatest weight gain, a brine shrimp level between the mid-and-upper levels in Test II is recommended for future studies. Both levels supported average weights in excess of 100 mg, and an intermediate level may eliminate the water fouling that occurred at the highest level of brine shrimp only. Additional E.P.A. criteria for an acceptable fathead minnow ELS test included an average survival not less than 80 percent, and a Relative Standard Deviation (RSD) of the final weights not greater than 40 percent. Survival during Test I was between 57 and 71 percent and ranged from 71 to 84 percent in Test II. The RSD was greater than 40 percent for five treatments in Test I, but was under 40 percent for all treatments in Test II.