Evaluation of microalgal diets for the intensive cultivation of the tropical calanoid copepod,Parvocalanus crassirostris

Abstract

As their natural prey, copepods are considered the ideal diets for hatchery culture of fish larvae. However, intensive cultivation of copepods has proven difficult and low culture productivity is the norm, which severely limits their use in aquaculture. This study investigated the effects of algal diets on a range of productivity-related parameters, including egg production, hatching success, naupliar and copepodite survival, post-embryonic development time, population growth and sex ratio of a small-sized tropical copepod, Parvocalanus crassirostris, which has been identified as a high potential species for aquaculture. The diets tested included three live algal diets: Isochrysis sp. (T-Iso), Pavlova 50 (Pav) and the diatom Chaetoceros muelleri (Cht); two algal paste diets: Isochrysis sp. (P-Iso) and Thalassiosira weissflogii (P-TW), as well as four mixed algae treatments composed of three binary algae diets (T-Iso + Pav, T-Iso + Cht and Pav + Cht) and a tri-algal diet (T-Iso + Pav + Cht). All parameters examined except sex ratio were significantly affected by the diets. The binary algal diet T-Iso + Cht produced significant higher total egg production over female lifespan (121.0 ± 5.9 eggs) than all other treatments (P < 0.05). Survival during naupliar and copepodite stage was significantly superior when P. crassirostris were fed either the mixed diet of T-Iso + Cht or the monoalgal diets of Cht or T-Iso (P < 0.05) than other diets. These three treatments also had the fastest time of development to adults (ranging from 6.2 to 6.7 days). With an initial 100 adults, the T-Iso + Cht treatment produced the highest population growth over a 15-day cultivation period, which was significantly higher than other treatments (P < 0.001). In contrast, the algal paste treatments, including (P-Iso) produced overall the worst results for various parameters examined. However, the sex ratio of P. crassirostris was not significantly affected by diets and was always heavily skewed towards females (>84% were females) across all treatments. Based on the results of this study, T-Iso + Cht is recommended for intensive cultivation of P. crassirostris.