Phenotypic Divergences in Growth and Reproduction Underpin the Invasion of Suckermouth Armored Catfish Pterygoplichthys disjunctivus (Loricariidae) into Lotic and Lentic Habitats in Vietnam

Suckermouth armored catfish (Pterygoplichthys disjunctivus) is one of the most widespread invasive species in Vietnam. However, it is relatively unknown how the species underwent its divergent adaptations to varying local conditions and habitat types, an understanding of which is essential for managing its invasion in Vietnam. We addressed this by analyzing a large number of fish (662 samples) collected in lotic (Dinh River) and lentic (Suoi Trau Reservoir) habitats in southern Vietnam during one year. The allometric growth patterns estimated by von Bertalanffy growth functions were L-t = 483(1 - e(-0.71(t 0.40))) in Dinh River and L-t = 346 (1 - e(-1.01(t-0.62))) in Suoi Trau Reservoir. The estimated fish ages were 2.9 to 4.2 years old with an average total length from 206.10 +/- 2.09 mm in Suoi Trau Reservoir to 319.22 +/- 3.29 mm in Dinh River. The percentage of fish with matured ovaries peaked in August (100%) and was lowest in February (<10%), indicating that these fish breed nearly all year round. The main reproductive season is April-October, with a peak in July-August, as indicated by the gonado-somatic index and monthly changes in the percentage of matured fish. The lengths at 50% maturity were 234.3 and 179.7 mm for females from lotic and lentic habitats, respectively. Lotic fish had a fecundity (4812 +/- 383 oocytes/ind.) which was five times greater than that of lentic fish (841 +/- 91 oocytes/ind.); however, the relative fecundity of the fish was not statistically different between the two habitats (approximate to 13 oocytes/g). This result was consistent with the larger oocytes: 2.95 +/- 0.04 and 2.58 +/- 0.01 mm for fish from Dinh River and Suoi Trau Reservoir, respectively. The faster growth and bigger fish with higher fecundity in the lotic habitats suggest that their population growth can accelerate more quickly, potentially affecting local communities more than those in lentic habitats. Our study sheds light on substantial phenotypic divergences in the reproduction and growth of the suckermouth armored catfish between lotic and limnetic habitats in Vietnam.