New records of alligator gar, Atractosteus spatula (Actinopterygii: Lepisosteiformes: Lepisosteidae) from Bali and Java, Indonesia

Alligator gar, Atractosteus spatula (Lacepède, 1803), is native to North America, with introductions reported from many countries. In 2019, two specimens of A. spatula were captured in Indonesia, one in the Nyanyi Estuary, a mangrove center in the south of Bali, and the other one in the Brantas River, the main river in the province of East Java. These records were among the first of this species from open waters in Bali Island and Java Island. A description of meristic and morphometric features of a specimen are provided.


INTRODUCTION
Alligator gar, Atractosteus spatula (Lacepède, 1803), is a predator fish native to North America, occurring from the Mississippi River basin, southwestern Ohio, southern Illinois, and the Gulf Mexico (Page and Burr 1991, Warren et al. 2000, Mendoza et al. 2002, Raz-Guzman et al. 2018) and now introduced to many countries worldwide as a consequence of the aquarium trade (Salnikov 2010). In Addition to North America, being its natural habitat, A. spatula was found in open waters such as Zrebar Lake, Iran (Esmaeili et al. 2017), Malay Peninsula, Malaysia (Chang et al 2017, and a coastal pond in Sumatra, Indonesia (Muchlisin 2012). Atractosteus spatula exhibits euryhaline, tolerance to new habitats, highly predatory habits, the eggs are poisonous, and the maximum recorded length was 305 cm (McClanes 1974). Because of this, A. spatula has the potential to become an invasive species (Mutlak et al. 2017).
Atractosteus spatula is commonly sold on the ornamental fish market (Raquel 1992, Cohen et al. 2007 and maintained in ponds for sport fishing (Mendoza Alfaro et al. 2008). Nyanyi Estuary is a mangrove center in the south of Bali, and the Brantas River is the main river in the province of East Java. No records of the aquarium trade and/ or sport fishing, however, have been reported from those two localities. The presently reported findings of A. spatula in Bali Island and Java Island constitute new records.

MATERIAL AND METHODS
We captured both specimens of the alligator gar using a cast net on 5 July 2019 in Nyanyi Estuary, south of Bali, and using landing net on 10 November 2019 in Brantas River, province of East Java. The fish were photographed and documented, although no voucher specimens were retained because the fish were too large to be stored and we did not have enough space in the laboratory. The determined meristic characters include the number of dorsal fin rays, pectoral fin rays, anal fin rays, ventral fin rays, and lateral line scales, while morphometric characters were: total length, standard length, head length, body depth, eye diameter, and snout length. The methodology followed Bigelow et al. (1963). The water quality parameters were determined directly at each location immediately after the capture.
Identification. Specimens collected in Nyanyi Estuary and Brantas River were identified as A. spatula. Atractosteus spatula can be distinguished from the other members of the family Lepisosteidae in having a large size and broad, with an elongated and triangular short snout. Specific morphological characters are as follows: cylindrical body with an obvious rounded tail, light dorsal stripe, dark olivaceous brown above and white to yellowish beneath, dark brown blotches on all fins (Fig. 2). Meristic and morphometric characters of A. spatula are given in Table 1.
We assumed that A. spatula was released by a fish owner, who frequently got rid of unwanted predator fish by releasing them into open water bodies. It was also likely that A. spatula were released because their excessive size and the owner was unable to maintain it (Boschung andMayden 2004, Chang et al. 2019 Fig. 1. Presently reported new records of alligator gar, Atractosteus spatula, from Indonesia; black triangle is the Brantas River, province of East Java, black square is Nyanyi Estuary, southern Bali (The map shows the province of East Java without Madura Island, which can be seen on the inset) North American data were from  and McDonald et al. (2013).
As the area does not have any aquarium trade and fishing sports pond, further investigation is warranted to determine the source of A. spatula in the Nyanyi Estuary and the Brantas River (Jagir Sluice). In the future, further introductions should be prevented to reduce the impact of invasive predator fish on the open waters on do not disturb on native aquatic ecosystems in Bali and Java (Speziale et al. 2017, Bize and Fernandez 2019, Hasan and Tamam 2019, Hasan et al. 2019). There are many native organisms in Nyanyi Estuary and Brantas River that can be affected by A. spatula, including through predation, so that the presence of A. spatula in both locations are danger alerts. Atractosteus spatula prey on almost all types of aquatic animals in the Nyanyi Estuary and Brantas River so that it can damage the food chain in these waters. If not captured, A. spatula can cause the loss of native aquatic animals.