Reproduction in Nonnative Environments: Establishment of Nile Tilapia, Oreochromis niloticus, in Coastal Mississippi Watersheds

Tilapia, in general, are known for their plasticity in growth, reproduction, and age- and size-at-maturity that not only make them an excellent aquaculture taxa but also allow them the ability to invade and become established in nonnative environments. We investigated aspects of reproductive biology and recruitment of the nonindigenous Nile Tilapia, Oreochromis niloticus, collected in the Pascagoula River watershed and from Simmons Bayou, a small tidal system of Biloxi Bay, Mississippi, over a 16-month period. Males ranged from 32.6–430.0 mm total length (TL) and females from 31.7–349.0 mm TL. The Gonadosomatic Index (GSI) for males or females indicated year-round reproduction with increased spawning intensity in spring (March to May) and in late summer (August to September). Small juveniles (≤ 25 mm TL) were collected every month of the year except March, and multiple size classes were collected suggesting successful recruitment of young. The smallest female with mature oocytes was 79.9 mm TL, and the size class where 50% of the females were mature was 113 mm TL. Batch fecundity (BF) ranged from 30–2603 oocytes for females, and there was a significant relationship between log10-BF and log10-TL and log10-BF and log10 EBW. Relative fecundity ranged from 0.89–11.75 oocytes/g EBW. Although Nile Tilapia have low fecundity, parental care essures that the majority of their eggs will survive to the juvenile stage. Low fecundity is further offset by the ability to spawn multiple broods throughout their year-round reproductive season. These reproductive characteristics may give the species a competitive advantage over native fishes. We expect Nile Tilapia to further invade and spread in these coastal watersheds.