Oreochromis urolepis hornorum
Rufigi tilapia and Wami tilapia were once recognized as separate species but is now viewed as subspecies of the same species instead. Their respective scientific names are Oreochromis urolepis urolepis (Rufigi tilapia) and Oreochromis urolepis hornorum (Wami tilapia).
The Wami tilapia, Oreochromis urolepis hornorum, derives its name from the African Wami River where it lives. The species is native to Uganda and Tanzania, and there is also an established population on Zanzibar but it remains unclear whether this population hails from introduced fish or not. Due to its popularity as a food fish, the Wami tilapia has been deliberately released into the wild in various parts of the world and specimens have also escaped from fish farms. Today, we can find established Wami populations in such diverse locations as Japan, Slovakia, USA, Cote d'Ivoire, Brazil, and Fiji. The Wami tilapia is occasionally kept in aquariums but it grows quite big – the largest scientifically measured Wami tilapia was 24 cm (9.5 inches) long – so you need a fairly big tank to house it in.
Oreochromis urolepis hornorum has not been evaluated for the IUCN Red List of Threatened Species. Its minimum population doubling time is less than 15 months, so it is a resilient species.
Wami tilapia can adapt to both freshwater and brackish conditions and is for instance thriving in saline ponds on Zanzibar. It can find food in most environments since it feeds on decomposing organic matter (detritus), small invertebrates, algae, and higher plants. One of the most important limiting factors for its spread into new environments is its poor resilience to low temperatures. This is a tropical fish that will do best when the water temperature is 22-26 ºC (72-79 ºF).
Adult Wami tilapias have large jaws which gives them a concave upper profile. Adult males are almost completely black, but the margin of the dorsal fin and the margin or upper half of the caudal fin is pink, bright red or orange, while the lips are black or pale. Female Wami tilapias are less spectacularly coloured; their bodies are silvery or steel grey with 2-4 mid-lateral blotches.
In tilapia farms, uncontrolled reproduction is a problem since it forces adult fish to compete with their offspring for food and space. This reduces growth rates and can lead to stunting and controlling reproduction is therefore important. When Wami tilapia mates with Mozambique tilapia (Oreochromis mossambicus), the resulting offspring consists of males to a very high degree. This scarcity of females means that you can keep such batches without having to worry about massive amounts of offspring in the growing unit. Male tilapias also grow faster and bigger than females. Wami tilapia is therefore an important fish for companies that produce tilapia fry for fish farms.
In the future, the Wami tilapia and its close relative the Rufigi tilapia might be moved to the genus Sarotherodon since Mitochondrial DNA studies have indicated that they might be more closely related to the members of that genus. The results are however difficult to interpret.