Investigation of ecological effects of the presence of non-native species in Shadegan International Lagoon

Unfortunately, the high diversity and high geographical spread of invasive species, e.g. tilapia species in Shadegan lagoon, has become one of the main challenges for the native fishermen and local communities in it. This study conducted field operations from October 2018 to September 2019. Laboratory experiments including the fish biometry, analysis of the biological parameters, the sexual maturity and nutrition were performed based on standard methods. The results of 898 sampling from different species of tilapia showed that fishing combination included 284 redbelly tilapia (Tilapia zillii) with 31.6 %, 578 Blue tilapia, (Oreochromis aureus), with 64.3% and Nile Tilapia, (Oreochromis niloticus), with 4%. The highest abundance of redbelly tilapia (Tilapia zillii) was observed in the length range of 11-13 cm, Blue tilapia, (Oreochromis aureus), with a wide length range of 7-23 cm and Nile Tilapia, (Oreochromis niloticus), in the length range of 13-16 cm. At present, the distribution of three invasive species of tilapia in Shadegan lagoon with more than 50% fishing during the most of months on the year along with unfavorable environmental conditions specially, reduction of quality and quantity of inlet water due to the agriculture and industrial Effluents and dam construction and reduction of water volume, lagoon become in a challenging situation.