Development and egg production in Centropages typicus (Copepoda : Calanoida) fed different food types: a laboratory study

The effects of different types of food on the growth, development, reproduction, egestion and grazing of the copepod Centropages typicus Kroyer was studied in the laboratory at 15degreesC. The copepods were reared from eggs to NVI using Isochrysis galbana as food, and from NVI onwards with a range of diets: a single food source consisting of 1 of 2 algae (the haptophyceaen Hymenomonas elongata and the diatom Thalassiosira weissflogii), a single food source consisting of the ciliate Strombidium sulcatum, and a mixture consisting of each type of algae and the ciliate. The results, based on daily sampling, show that growth, development rate and egg production were dependent on food type. The food types that induced the shortest development times (H. elongata, S, sulcatum) did not necessarily result in the highest production rates. The daily specific growth rate for copepodid stages was significantly lower with T. weissflogii (0.045 d(-1)) than with the other diets (0.09 to 0.15 d(-1)). The combination of variable development and variable growth rates with the different diets induced a high variability in mean weight within developmental stages. The weights recorded are amongst the highest observed for this species. Length did not differ significantly within the same development stage between different diets. Mixed food sources were more efficient than a single food source in terms of egg production and viability. No relationship was established between hatching success, female age or copepodid mortality rate and food type. A pure diet of T. weissflogii resulted in a sex ratio skewed towards males, whereas the other diets produced a balanced sex ratio. The present results indicate the mixture phytoplankton/ciliate to be the most favourable for development, growth and egg production, suggesting that omnivory is the best feeding strategy for C. typicus.