Rearing experiments with five species of Australian freshwater fishes. II. Morphogenesis and ontogeny

The eggs, embryonic development, and larvae of five species of fish, endemic to Australia, are described and compared. They are Tandanus tandanus, Plectroplites ambiguus, Maccullochella macquariensis, Bidyanus bidyanus, and Carassiops klunzingeri. Plectroplites ambiguus and B. bidyanus both have pelagic eggs with diameters of 3.9 and 2.8 mm, respectively. Hatching times for these two species are similar being about 30 hr at water temperatures of about 25°C. The newly hatched larvae are at an early stage of development and average 3.2 and 3.6 mm in length, respectively. The eggs of T. tandanus are demersal, non-adhesive, average 3.2 mm in diameter, and are laid in a nest usually made in gravel or coarse sand. Hatching takes 6-7 days at a temperature between 20 and 25°C and the newly hatched larvae emerge at an average length of 7.1 mm. Maccullochella macquariensis lays eggs which are demersal and adhesive and this species utilizes hard objects such as the inside of sunken hollow logs for attachment of the eggs. Eggs average 3.4 mm in diameter, hatching can take place in 6 days at temperatures approaching 25°C but the larvae are at an earlier stage of development than those which hatch later. Under river conditions hatching probably takes place at temperatures nearer 20°C when they may take 10-14 days to hatch. Early hatched larvae may be only 6 mm in length: those which take longer to hatch, even at the same temperature, are usually about 9 mm in length. The eggs of C. klunzingeri are very small, ovoid, and when water-hardened may vary in diameter from 0.4 to 0.5 mm. Hatching takes place in 47-53 hr at a temperature range of 18-23°C. The larvae average 1.9 mm when newly hatched and are undeveloped. Observations on the early life history of Perca fluviatilis, an introduced species, are also described. These observations indicate that high minimum water temperatures before spawning or during growth of the embryo may contribute to the control of the distribution of this species either by causing damage to the oocytes of the adult fish or by premature hatching of the eggs. High summer water temperatures alone, were previously accepted as the reason for the control of the distribution of this species.