Observations on the biology of smooth dwarf monocle bream, Parascolopsis aspinosa (Rao & Rao, 1981) from Mangaluru, southwest coast of India

Abstract

Some aspects of biological information is presented here for the little known smooth dwarf monocle bream, Parascolopsis aspinosa (Rao and Rao, 1981) (Perciformes: Nemipteridae) based on specimens collected from the bycatch of commercial shrimp trawlers operating in the Arabian Sea off the Karnataka coast. Eight-hundred forty seven specimens measuring 7.4 to 22.8 cm TL, and weighing between 15.0 -216 g total weight were analysed for the study. The length-weight relationships were found to be significantly different between the sexes (P<0.001). The coefficients ‘ a’, ‘b’ of the length-weight relationship were estimated as 0.0333, 2.7919 (r 2 = 0.961) for females and 0.0194, 2.9791 (r 2 = 0.962) for males and the species follows a negative allometric growth pattern (b<3). The fish attains maturity (TL 50 ) at 12.5 cm TL for females and 11.5 cm TL for males. P. aspinosa was found to breed throughout the year with peak spawning during August-September and January. The overall sex ratio (M:F) favoured females at the rate of 1:1.15. A seven-stage maturity was found and a progressive increase in the size of the ova was traced to advanced stages of maturity. The total fecundity of P. aspinosa ranged from 45,823 (12.3 cm TL; 41g body weight) to 1,56,308 (22.8 cm TL; 216 g body weight) with an average fecundity of 84,367 eggs. Analysis of the stomach contents (%IRI) revealed that P. aspinosa mainly fed on Saurida tumbil (%IRI=18.2), followed by Penaeus indicus (%IRI=16.7), Loligo spp. (%IRI=15.2), Squilla (%IRI=6.4), and Acetes spp (%IRI=2.7). Other detailed biological observations such as the length composition, sex ratio, and length at maturity (TL 50 ) of P. aspinosa are also provided in the study. Since the species has been poorly studied and assessed as Least Concern (LC) in the IUCN red list criterion, it is expected that the biological information from the present study will support the ongoing data generation and help in arriving at management decisions for the species in the future.