Term of Award

Spring 1995

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Committee Chair

Stephen P. Vives

Committee Member 1

James B. Claiborne

Committee Member 2

David C. Rostal

Abstract

The loach minnow, Tiaroqa cobitis, and the spikedace, Meda fulqida, are two threatened cyprinid species which continue to decline in numbers. Anthropogenic destruction of habitat is the primary reason for decline of these minnows, and hatchery propagation may be necessary for their recovery. Examining the effect of photoperiod on triggering reproduction from a nonbreeding state in both species, determining preferred spawning substrates and shelters for each fish, and studying territorial interactions in the loach minnow are the three primary objectives of this study.

In order to develop hatchery methods, we tested four aquariums for each species, in which a more natural photoperiod group was observed but the photoperiod was increased 15 min., which concurs with the approximate light increase in spring in Arizona. In four separate aquariums for each species, the photoperiod was increased weekly (30 min.). This approximately doubles the increase of light in the spring in Arizona. Although spawning did not occur in either species, a definite reddening of the pectoral, pelvic, and caudal fins in male loach minnows was observed.

Substrate choice of both species was also examined. The loach minnows were given a choice of slate, PVC, and tile shelters. While the spikedace were given a choice of gravel, sand, and artificial plants. When data were statistically analyzed, male loach minnows showed no preference; female loach minnows used slate more than expected by chance. Spikedace preferred sand and gravel more often and plants less often than expected by chance.

Finally, because territoriality requires a large amount of energy, an organism may minimize this energy cost by reducing aggression towards neighboring residents. This hypothesis is known as the dear enemy phenomenon. An experiment was used to determine if this effect exists in loach minnows. Pairs of loach minnows of the same sex were tested. After one week a fish from each treatment aquarium was switched from each treatment aquarium, and one fish in each control aquarium was netted and returned to the same residence. Agonistic interactions were recorded between each resident. Data supported the dear enemy hypothesis in loach minnows because the number of agonistic interactions to neighbors were significantly less than interactions to strangers.

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