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More than 1500 measurements were made of mature eggs from females obtained from two populations of central Texas darters (Etheostoma spect- abile from the Llano River at Junction and Etheostoma lepidum from the South Concho River 4 miles south of Christoval). Junction eggs averaged 1.515 + 0.002 mm and those from the South Concho 1.301 ? 0.031 mm. Female size did not seem to influence egg size, with small eggs as likely in large as in small females. Eggs from females collected in November and April were smaller than those from fish of the same population collected in December through March. More than 2500 counts were made of egg complements of females from the same two populations. The number of eggs increased geometrically with female size, and the rate of increase approximates a squared relationship. Apparently digestive absorptive surface is more limiting than coelomic space. The largest females may have fewer eggs than medium sized females, especially toward the end of the breed- ing season. Females collected in February and adjacent months have more eggs than those obtained in other months. The difference is caused by more eggs in equivalent sized females. The fecundity of an animal is the product of frequency of spawn- ing and number of eggs produced per spawning interval. Although egg number would appear to be rather easily ascertained, little is known about spawn variability or factors causing it. The potential maximum number of eggs in a female is the result of available dis- tended coelomic space divided by average egg volume. Either volume varies among females or maximum potential is seldom achieved, be- cause spawn variation has been demonstrated and is obvious in our counts. Therefore, egg number in fishes may be limited by several factors including available coelomic space and nutrition. Sviirdson (1949) pointed out that equivalent-sized females can pro- duce large numbers of small eggs or small numbers of large eggs. A female could concentrate her nutrients in a few eggs, each of which would have a high survival potential, or spread them over many small eggs, each with low survival potential. Genetically controlled differ- 301 |
