Biology of the Gila Spikedace, Meda fulgida, in Arizona

Abstract

Gila spikedace, Meda fulgida Girard, of Aravaipa Creek, Arizona, were studied from June 1966 through July 1967. Sexual dimorphism in nonbreeding fish was slight; breeding males were brilliant yellow. Tuberculation was pronounced in males, but occurred in both sexes. Spawnings were observed in slowly flowing water less than 15 cm deep, over sand and gravel bottoms. Males patrolled specific areas, but no territorial defenses were observed. Females moved to spawning areas and apparently directed reproductive activities; spawning was in midwater and more than one male attended a female. Sexual maturity was attained at about 40 mm by both sexes. Sex ratios changed from 1:1 in young to a larger number of females in old adults. Reproduction extended from March through May. Ova attained diameters of 1.35 to 2.0 mm (mean 1.65) and the ovaries ranged from 19.5 to 30.0% of body weight (mean 24.3%) in mature females. Egg numbers, the sequence of maturation of eggs, and dates of appearance of young indicated two sets of ova produced per season, at least by females of age group II. Females of age group I produced 122 -+ 16 ova/complement and age group II produced 207 ?-t 47. The relation between numbers of ova and body size was adequately described by a straight line. Age groups were readily defined by length frequencies. Growth was greatest up to ca. 40 mm, then was relatively constant at a lower rate throughout life; maximum size was about 65 mm (age group III), and few fish live a third summer.