Prey selection by greenback flounder Rhombosolea tapirina (Gunther) larvae

The potential for greenback flounder (Rhombosolea tapirina), as a new species for aquaculture in temperate Australia, is currently under investigation. Isolation of an endemic temperate rotifer, Testudinella sp., provided the opportunity to assess this genus against standard live prey species used in aquaculture. Greenback flounder larvae were offered a range of rotifer prey species (Testudinella sp., Brachionus rotundiformis, Brachionus plicatilis) and the brine shrimp Artemia, either in isolation or combination, in order to test the hypothesis that factors besides prey size affect prey selection. From first-feeding to approximately day 13 post-hatching, greenback flounder larvae preferentially consumed the rotifer Testudinella sp. over the larger width rotifer B. plicatilis and to a lesser extent the rotifer of similar width dimension, B. rotundiformis. From day 15 post-hatching, consumption (number of prey consumed per larva per unit time interval) and selection (α) of B. plicatilis was significantly higher than of Testudinella sp. and Artemia, but by day 18 post-hatching, there was a shift of feeding preference to Artemia. This indicated that size of prey ingested increased with age, likely reflecting an ontogenetic increase in larval sensory function, mouth gape and prey capture and handling ability. Significant selection of Testudinella sp. over the larger rotifer B. plicatilis occurred despite greenback flounder larvae being able to consume B. plicatilis. This along with significant selection (day 11 post-hatching) and consumption (days 11 and 12 post-hatching) of Testudinella sp. over the rotifer of similar width B. rotundiformis, indicates that prey size is not the sole determinant of prey consumption and suggests that greenback flounder larvae exhibit both species-specific and size-specific prey selection. Understanding the basis of prey selection by larval fish predators is essential for enhancing prey consumption in culture, especially in the context of ontogenetic shifts in prey species preference.