First record of the invasive Nile Tilapia , Oreochromis niloticus ( Linnaeus , 1758 ) ( Perciformes , Cichlidae ) , on Bawean Island , Indonesia

In 2018 we captured specimens of Oreachromis niloticus (Linnaeus, 1758) from Danau Kastoba, a crater lake on Bawean (Indonesia), a small, isolated island in the Java Sea. Additional individuals were later photographed. These records are among first of this species from an isolated island, in the Java Sea. A description of meristic and morphometric features of a specimen are provided.


Introduction
Oreochromis niloticus Linnaeus, 1758 is a tilapia native to the Nile (Africa) and now introduced to many countries worldwide for aquaculture (Ishikawa et al. 2012).Oreochromis niloticus exhibits fast growth (Qiang et al. 2014) and tolerance to new habitats (Kulac et al. 2014, Abdel-Tawwab 2015).Because of these attributes, O. niloticus has the potential to become an invasive species and compete with other fish species for resources (Gu et al. 2015).
In Indonesia, O. niloticus is generally spread in mainland waters where aquaculture activities have been underway for some time (Basuki and Sri 2014).Bawean, a small, isolated island in the Java Sea, is a fisheries center, but there is no record of culturing tilapia there.The existence of O. niloticus on Bawean constitutes a new record.

New records. (Figs
Identification.Meristic and Morphometric characters of O. niloticus are given in Table 1.Other specific morphological characters are as follows: scales cycloid; gill rakers short; 3 rows of scales on cheek; maxilla and lower jaw equal; teeth widen; pectoral fin pointed; dorsal, pectoral and anal fins blunt; caudal scaly.Coloration: anal fin faintly barred; caudal and soft dorsal fin sharply barred; about 9 narrow dark bars on sides body; dark blotch at corner of operculum.

Discussion
Oreochromis niloticus has been introduced to more than 90 countries around the world for both fresh and brackish water aquaculture (Fitzsimmons 2001).This species is one of the top 10 introduced species of animals in the world (Picker and Griffiths 2011).
Indonesia is the second largest producer of O. niloticus in the world after China (FAO 2017).Due to intensive aquaculture, O. niloticus now occurs in all fresh and brackish waters of mainland Indonesia.Its presence on the island of Bawean, in the middle of Java Sea and 153 km from the nearest maindland (Fig. 3), is new record.
We speculate that O. niloticus was released into Danau Kastoba on Bawean by local people.The purpose is not clear.As the island does not have an aquaculture industry, further investigation is warranted to determine the sourch of O. niloticus on Bawean Island.The control and prevention of further introductions is needed so that O. niloticus on does not disturb the natural ecosystem (Speziale et al. 2012).

Figure 1 .
Figure 1.Location of Danau Kastoba on the island of Bawean in the Java Sea.