Embryonic and larval development of the suckermouth sailfin catfish Pterygoplichthys partialis from Marikina River, Philippines

Background: There is little information about the early development of this invasive fish species in order to understand its early life history and developmental strategies towards invasion. Material and Methods: Female Pterygoplichthys pardalis were induced to spawn using human chorionic gonadotropin (HCG) so as to study the developmental stages from fertilization until yolk resorption. Results: The females subjected to a single dose of HCG responded positively to treatment (97%) with higher fertilization success (88%) compared to the untreated females (21%). Nonetheless, the HCG-induced fertilized eggs had a low hatching success (49%), while from the free-living embryos successfully hatched, a high number (90%) survived to become juveniles. Embryonic development in P. pardalis was completed 168 h and 30 min after fertilization, with the total yolk resorption completed on the 8t h day post hatching, during which the suckermouth gradually shifted from rostral to ventral position to commence the loricariid algae-scraping feeding mode. Conclusions: Pterygoplichthys pardalis does not undergo a true larval metamorphosis between the free-living embryo and the juvenile stage and a definitive adult phenotype is developed directly. These results provided basic, yet essential information on the early developmental features of this invasive species whose spawning and early developmental strategies were difficult to observe in the field. Implications of some ontogenetic features in this species with regards to invasion are also discussed.