Effect of adult density on egg production, egg hatching success, adult mortality, nauplii cannibalism and population growth of the tropical calanoid copepod Acartia tropica

Abstract

Present study evaluated the impacts of adult density on key biological parameters of a tropical estuarine calanoid copepod A. tropica. Egg production, egg hatching success (EHS), adult mortality (%), nauplii cannibalism (% hour−1), population growth and intrinsic rate of population increase in response to five different adult densities viz. 125, 250, 500, 1000 and 2000 adults/L were assessed. The highest individual egg production (IEP, eggs/female/day) was recorded at 125 adults/L treatment while relative egg production (REP, eggs/L/day) was highest at 1000 adults/L. EHS (24 h and 48 h) showed significant difference (p < 0.05) among the treatments with highest EHS recorded at 125 adults/L treatment and lowest EHS recorded at 2000 adults/L treatment. Moreover, the adult mortality and nauplii cannibalism were negatively correlated to adult density with significantly highest cumulative adult mortality (65 ± 3) and nauplii cannibalism (4.49 ± 0.27) recorded at 2000 adults/L. The highest population count after 8 days culture was recorded at 2000 adults/L treatment. However the lowest intrinsic rate of whole, live and adult population increase after 8 days culture was recorded at 2000 adults/L treatment. It is also observed that the population with an initial adult density of 2000/L decreases to a new stable equilibrium of 1000 adults/L after 8 days culture. Our results suggest to maintain A. tropica at a density of 1000 adults/L in batch culture with daily harvest of eggs and nauplii to maximise its productivity as live feed in aquaculture hatcheries.