Knight, J. T., Butler, G. L., Smith, P. S. and Wager, R. N. E. 2007. Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley. Journal of Fish Biology 71, 1494-1511.

Summary

The Oxleyan pygmy perch Nannoperca oxleyana is a small, freshwater fish that inhabits the coastal heathlands of northern New South Wales (NSW) and southern Queensland. The species is listed as endangered and a recovery plan has been prepared by the NSW Department of Primary Industries to guide conservation and management programs. A lack of biological information is recognised as a major impediment to developing effective recovery actions with reproduction being one of the least known aspects of the species’ biology.

The reproductive biology of Oxleyan pygmy perch was described from studies of wild populations in north-eastern NSW and mature fish held in aquaria. Reproduction of captive fish mirrored that of the wild populations and provided additional insights into the species’ biology. In the wild, 50% of males and females became sexually mature at lengths of 24-25mm and 28-29mm, respectively. During the breeding season, the body and tail of males took on an intense red colouration and most of the other fins darkened. Females undertook a similar but less intense, colour transformation. Captive males defended artificial weed in which pairs of fish spawned and fertilised eggs. Video footage of this behaviour is available below. Repeated spawning by wild and captive fish occurred from September to April/May when average water temperature and day length reached or exceeded 16.6°C and 10.7 hours, respectively. Captive fish spawned on an average of 146 (57%) of days during the 256 day spawning period. The average number of eggs spawned in a day by captive and wild females was low at 7.8 eggs per fish. The total number of eggs spawned by captive females during the breeding season was also low, averaging 1323 eggs per fish. However, relative to body weight, the total number of eggs spawned was high, averaging 587 eggs per gram of fish.

The spawning behaviour of Oxleyan pygmy perch may reflect an adaptation for survival in the harsh, variable environments it lives in. The continuous production of numerous small batches of eggs might allow for reproductive success during favourable conditions, while the loss of a few batches during harsh periods may not be critical because of the relatively small amount of energy invested in reproduction per spawning event.

Video details

This video shows the breeding behaviour of the endangered Oxleyan pygmy perch. It was recorded by Jamie Knight, Scientific Officer with the NSW DPI who studied the breeding behaviour of this small native freshwater fish held in aquaria at the Port Stephens Fisheries Centre as part of his Doctor of Philosophy Degree.

The video commences with the female swimming near the bottom left corner of the tank. The male appears at the back of the tank, and aggressively chases the female away from the black artificial weed lying on the bottom. From the top of the tank, the female approaches the male. The male then guides the female into the weed where they release milt and eggs, respectively. The male then aggressively chases the female away from the weed. This aggressive behaviour by the male may represent a form of territoriality and parental care, defending spawning sites and guarding eggs and young fish from predators. The overall pattern of breeding activity is repeated in the same area of the tank and then in the back left corner in the weed suspended vertically in the water column.

The video footage provides valuable insights into the biology of this threatened species. The continual pattern of spawning shows that this species is a serial spawning fish that repeatedly spawns small numbers of eggs every few days throughout the spawning season, which extends for 8 to 9 months during the warmer part of the year. This contrasts with the spawning behaviours of other native fish such as Murray cod, which spawns a large number of eggs in a single event.

This information is being used by the NSW DPI to develop effective recovery actions to protect and manage the remaining populations of this threatened species in north-eastern NSW and south-eastern Queensland. The recovery plan for the Oxleyan pygmy perch can be viewed at http://www.fisheries.nsw.gov.au/threatened_species