Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley

摘要

The reproductive biology of the Oxleyan pygmy perch Nannoperca oxleyana is described from simultaneous studies of wild populations in north-eastern New South Wales and mature fish held in aquaria. In the wild, 50% of males and females matured at total lengths of 24.0-25.9 and 28.0-29.9 mm, respectively. The species displays sexual dichromatism during the spawning season, with males developing more intense red and brown fin and body colouration, and black pelvic fins. Captive male broodfish displayed territoriality during the breeding season, closely guarding sites within artificial, plant-like substrata in which pairs of fish spawned adhesive eggs. Protracted serial spawning of wild and captive fish occurred from September to April and May at mean water temperatures greater than or equal to 16.6 degree C and day length greater than or equal to 10.7 h. Captive broodfish spawned on an average of 57% of days during the 256 day spawning period. Gonado-somatic indices averaged 0.7% for all ripe males and 4.1-4.2% for all ripe females collected. Mean total and batch fecundities of captive females were 1323 eggs per fish and 7.8 eggs per fish per day, respectively, and relative fecundity was 587 eggs g super(-1) of body mass. Batch fecundity of wild females was estimated at 7.8 eggs per fish. The adaptive significance of this reproductive strategy in a harsh, variable environment is discussed.