Reproductive and feeding biology of the protogynous rice paddy eel Monopterus albus

• Main Author: Nisperos, Dulce Marie P.
• Format: text
• Language: English
• Published: Animo Repository 2022
• Subjects: Snake eels; Synbranchidae; Estradiol; Testosterone; Biology
• Online Access: https://animorepository.dlsu.edu.ph/etdd_bio/3; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=1003&context=etdd_bio
• Institution: De La Salle University

The rice paddy eel Monopterus albus is an introduced species in the Philippines and was first recorded in the country in 1918. There is potential for breeding of the species for culture, a practice common in Thailand, Vietnam, and China. However, there is also the possibility that the proliferation of the species may lead to unwanted effects such as biodiversity loss and habitat destruction. This study provides basic information on the growth and reproduction pattern, reproductive potential, and feeding biology of this protogynous species for use in proliferation control of the species or if later allowed, in aquaculture development in the Philippines. M. albus was collected opportunistically from four different sites in Luzon. Several sets of data from a total of 1683 samples were used to (1) determine pattens of growth, size structure across sexes and size at sexual maturity; (2) establish seasonality of reproductive stages, fecundity, and reproductive capacity; and (3) compare the condition factor, levels of sex- change related hormones and diet preferences across sex stages. The study presents the first report of length at first maturity of females (37.95 cm) and length at first sex change (67.2 cm) for a population of M. albus in the Philippines. The numbers are slightly higher than the average reported for the species. Females were the most frequent sex stage in the population throughout the year compared to intermediates and males. Though limited in the number of samples, results of the comparison in estradiol and testosterone levels across female, intermediate, and male M. albus suggest that other hormones aside from testosterone and estradiol should be investigated in terms of how these hormones control sex transition. The prolonged period of breeding and egg production peaks in February to August was consistently observed for the species in two populations. The success of the females all year and the extended breeding season through the dry months from November to February may be because M. albus females are opportunistic and non-selective carnivores, while the intersexes and male diets are primarily gastropods. Body condition is highest for intermediates compared to males or females for feeding activity is higher and energy requirement for gonad development is low until they transition into males. Most males survived with less feeding by conserving their energy output while caring for the offspring within their nest. The information regarding the reproductive and feeding patterns in rice paddy eels are prerequisites to facilitate appropriate management initiatives and sustainable exploitation of this species in the Philippines. Keywords: diet, estradiol, feeding activity, Monopterus albus, protogynous hermaphrodite, reproductive patterns, sex change, and testosterone