The effects of algal diets on population growth and egg hatching success of the tropical calanoid copepod, Acartia sinjiensis

Abstract

As natural diets of fish larvae, a number of calanoid copepod species are being investigated for use as live prey in aquaculture hatcheries. One of these, the tropical calanoid copepod, Acartia sinjiensis, has good potential as a live feed for tropical reef fish larvae. However, the rearing techniques for A. sinjiensis require further development to improve productivity. This study was carried out to investigate the population growth and egg hatching success of A. sinjiensis when fed a range of mono-and binary algal diets, including algae in the form of frozen paste.

For the population growth experiment, the final A. sinjiensis population, including eggs, nauplii, copepodites and adults, was determined after feeding eight algal diets (two frozen algae, four live monoalgal and two live binary algal diets) for 8 days at temperature 28 ± 1 °C; salinity 34 ± 1 psu and photoperiod 12 L:12 D. Five replicates, with an initial 12 adult A. sinjiensis per replicate, were set up for each treatment. In a separate experiment, effects of diets on egg hatching success were examined after 48 h incubation of eggs produced by A. sinjiensis fed the same eight diets.

The results showed that diet significantly affected both population growth and hatching success of A. sinjiensis. Of the diets tested, the binary algal diets were more successful than monoalgal diets, while the frozen algae had little dietary value. The highest population growth was recorded on A. sinjiensis fed a binary diet of Tetraselmis chuii and the Tahitian strain of Isochrysis sp. (T-ISO) (final population: 1091 ± 80), which was significantly higher (P < 0.001) than all other diets tested except for the other binary diet of Nannochloropsis sp. and T-ISO (final population: 897 ± 123). Diet also had a significant effect (P < 0.001) on egg hatching rate, though the highest hatch rate was recorded with eggs produced by A. sinjiensis fed binary diet Nannochloropsis sp. and T-ISO (88.1 ± 2.1%), this was not significantly different from that of eggs produced by A. sinjiensis fed either T-ISO alone (88.0 ± 1.7%) or the binary algal diet of T. chuii and T-ISO (76.4 ± 7.1%). The results of this study suggest that among the diets tested, a combination of live T. chuii and T-ISO was the best for the culture of A. sinjiensis.