Spawning, development, and temperature tolerance of the spangled perch, Madigania unicolor (Gunther), from inland waters in Australia

Abstract

Spangled perch were bred in ponds on four occasions during which their breeding requirements and details of their embryonic development could be studied. They commenced spawning around November when surface temperatures reached 26.0°C and bottom temperatures 20.0°C. Flooding helped to induce breeding but was not essential.

The eggs, which were demersal and dispersed randomly over the bottom of the pond when spawned, were spherical, transparent, predominantly non-adhesive, possessed a single oil globule, and varied from 0.67 to 0.81 mm in diameter. The time taken for hatching at temperatures between 23.0 and 26.4º C was approximately 2 days 2 hr, and the newly hatched larvae measured between 1.72 and 2.56 mm in length.

Embryological development was recorded in detail. The prolarval stage terminated at about 3 days 18 hr (ie. with complete absorption of yolk), and the postlarval stage at approximately 24 days 4 hr after hatching. Juvenile fish possessed a yellow mark above a black mark on the proximo-ventral edge of the caudal fin, a character not mentioned by earlier workers. The maximum recorded size of an adult fish was 567 g. The fecundity of adult females varied from 24,000 eggs for fish weighing 24 g to 113,200 eggs at 65 g.

The approximate LD₅₀ values for minimum and maximum lethal temperatures of juveniles were 5.3º C and 39.0°C respectively. The lower lethal temperature appears to limit Australian distribution of this fish. Little experimental evidence was obtained to support the phenomenon of aestivation reported by previous workers. Aspects of the species survival in the extreme climatic conditions in which it occurs are discussed.