Effects of crushed conspecifics on growth and survival of Penaeus monodon Fabricius post larvae

In the present study, the hypothesis tested was that Penaeus monodon post-larvae (PL) experience lower growth when exposed to crushed conspecifics, which was achieved by exposing individual P. monodon PL with abundant food for 4 weeks to a gradient from 0 to 100 crushed conspecific PL L1. Both dry weight (48.5±7.2 mg) and body size (28.0±1.3 mm) of animals exposed to 1 macerated PL L1 were significantly (P¿0.011) higher than those of animals in treatments with 0, 5 and 10 crushed PL L1 (average over treatments: 25.6±3.2 mg; 23.4±0.5 mm). All animals died within 1 week when exposed to 70 and 100 crushed PL L1, and within 3¿4 weeks when exposed to 50 and 30 crushed PL L1. Exposure time affected mortality and it appeared that LC50 values decreased from 60 to 13 crushed PL L1 from 1 to 4 weeks' exposure. Survival of P. monodon PL was negatively correlated to pH, biological oxygen demand, ammonia and nitrate. In conclusion, low dose of crushed conspecifics has a stimulatory effect on P. monodon PL, as larvae were heavier and larger, while high doses cause high mortality.