Feeding behaviour of greenback flounder larvae, Rhombosolea tapirina (Gunther) with differing exposure histories to live prey

This study examined the feeding performance of cultured larvae of the greenback flounder Rhombosolea tapirina, using the live feed organisms, Brachionus plicatilis and Artemia sp., to determine the primary sensory modality involved in feeding, and the effect of previous exposure to prey on subsequent prey selection. The proportion of larvae that fed on rotifers in the light (400–700 nm daylight fluorescent tubes — light intensity of 5–6 μmol s−1 m−2), increased significantly from 66% to 96% from day 12 to day 27 post-hatching, respectively. In comparison, the proportion of larvae that fed on rotifers in total darkness, never exceeded 5% during the same period. This indicates that greenback flounder larvae are primarily dependent upon vision to feed. Prior feeding experience of greenback flounder larvae with either rotifers only (R-treatment) or a mixed diet of Artemia and rotifers (A&R-treatment) significantly affected subsequent prey selection when larvae were offered a mixed diet of Artemia and rotifers. It did not, however, affect the temporal onset of selection of the novel prey species (Artemia) by R-treatment larvae. Therefore, the differences in prey selection by larvae, with or without prior exposure to Artemia prey, were not due to the inability of larvae to handle and ingest a novel prey species, but they reflect positive selection for familiar prey. The latter indicates a learned component in the feeding behaviour of fish larvae. This has implications for the timing of the introduction of new live prey species during intensive culture of marine fish larvae

Distribution, movements and diet of nocturnal fishes on temperate reefs

We counted nocturnal fishes both day and night, and monitored the position of tagged individuals on temperate reefs in New South Wales, Australia. Pempheris affinis and P. multiradiata were the most abundant nocturnal planktivores on Sydneyrsquos rocky reefs and showed great differences in diel migration behaviour. Both species were observed in deep shelter sites during the day (5–10thinspm), and most emerged into the water column at night. P. multiradiata was found to undergo extensive vertical and horizontal migrations. In contrast, P. affinis remained within daytime depth strata, with tagged individuals often moving less than 20thinspm at night. Tagged adult P. affinis returned to tagging sites for up to 7thinspweeks, indicating high site fidelity. Dietary analysis demonstrated that small and large pempherids differed in diet and the timing of foraging, suggesting a size-based transition from diurnal to nocturnal foraging. Stratified sampling of planktonic assemblages at different depths during the day and night showed spatial variation in the availability of prey items at different times of the day. Amphipods, the main prey of large fish, were only available during the night, and concentrated in shallow water, whereas decapod larvae, consumed mainly by small fish, were abundant day and night. Large P. affinis also fed on polychaetes, which were never found in the stomachs of P. multiradiata, suggesting that these species may have different prey requirements, or that these polychaetes are only found in deep water where foraging P. affinis were abundant. We found no general model for the Pempheridae. The movements and behaviour of nocturnal fishes varied greatly by species, and this may be due to differences in body size, and/or physiological (e.g. visual ability) and ecological constraints