Early development of eel-tailed catfish, Tandanus tandanus (Mitchell) (Teleostei : Plotosidae), with validation of daily otolith increment formation

Eel-tailed catfish, Tandanus tandanus, have recently experienced widespread population declines in eastern Australia; with some southern populations facing the risk of extinction, the management and conservation of Queensland populations should be considered a priority. There is a lack of sound, scientific knowledge surrounding the species’ reproductive patterns and early life-history requirements. To assist in clarifying the influence of changes to the natural environment on the reproductive ecology of T. tandanus, we investigated their early life history using naturally fertilised eggs and larvae from a wild population. Nest depth ranged from 0.20 m to 1.35 m, with in situ temperatures between 15.1°C and 29.9°C, and in situ velocities from 0.00 to 0.52 ms–1. Eggs ranged in diameter from 2.6 to 4.0 mm throughout development, and preservation of eggs in ethanol caused significant shrinkage (mean 18.9%). Hatching took 4–7 days (mean 5.29 days; 15.7–28.0°C). Larvae collected from nests ranged in length from 5.1 mm to 15.3 mm SL, and in age from one day old to 16 days old. Larvae are likely to actively disperse from their nest at ~16 days old, as they approach juvenile metamorphosis. Daily otolith increment formation was validated up to 28 days after hatching; and sagittal otoliths were used to develop an age–length relationship for larvae. These results can assist researchers in estimating the timing of critical recruitment events, and investigating how the species’ early life history is influenced by environmental conditions.