Salmo trutta Linnaeus, 1758

Gurumayum, Shantabala Devi, 2021, A report on the occurrence of two exotic cold-water fishes in the natural water bodies of Arunachal Pradesh-Northeast India, Records of the Zoological Survey of India 121 (4), pp. 499-503 : 500-502

Salmo trutta Linnaeus, 1758

1758. Salmo fario Linnaeus , Systema Naturae, Ed. X.

Holmiae. v. 1: i-ii + 1-824.

1987. Salmo trutta : Lelek, Threatened fishes of Europe. Aula-Verlag, Wiesbaden. 9: 105.

Common Name: Brown Trout.

Materials examined: 1 ex, Yangyup river, a tributary of Siyom river, Mechuka , Shi-Yomi District , Arunachal Pradesh with the geographical coordinates of 28.5314 North 94.1242 East (Not registered)

Distribution: It has wide geographical range of distribution. The native range of the fish is Europe, northern Africa, and western Asia ( Page and Burr 1991).

Remarks: The species is identified as Invasive and other problematic species, genes and diseases category as per IUCN and also listed in the Global Invasive Species Database (2019). The effects of Brown Trout on local population were done by researchers like Nyman (1970), Waters (1983) and DeWald et al., (1992) and showed that the species been implicated in reducing native fish populations through predation, displacement, and food competition. McAfee 1966 opined that the species is responsible for the near-extinction of some species. There are also reports of hybridization with natives though occurs very rarely ( Brown 1966). However, introductions failed to establish populations in natural water bodies since natural reproduction of the species is low or nonexistent in most of the states where it has been introduced. However, if the fish population is maintained with periodic stoking the species may also reproduce in the natural water ( Courtenay et al., 1984).

The fish was introduced in India in the year 1863 from the UK and to the state 1967 as a game fish and for cold water fishery programme. In India, very negligible research has been done on the impact of the species on the local fish population, especially in biodiversity rich areas ( Singh et al., 2013; Swain et al., 2017). Since there is no concrete evidence to prove that the species has established in the natural water bodies in India, the species has been using for aquaculture purpose by the different state fisheries departments of India, including Arunachal Pradesh. However, the release of the brood of such species in natural water bodies by risking the fragile ecosystem should not be done especially in the biodiversity hot spots area because of its other confirmed report of negative effects on the natural ecosystem and also because of the unpredictability of nature. Under the coldwater fishery programme, the state fishery department along with Directorate of Coldwater Fisheries Research, ICAR established trout stocks in the districts, so getting the species from nearby river and stream is anticipated.

Genus Oncorhynchus Suckley 1861

Oncorhynchus mykiss (Walbaum 1792)

1792. Salmo mykiss Walbaum, Ichthyologiae pars III. Ant.

Ferdin. Rose, Grypeswaldiae [Greifswald]. Part 3: [i-viii]

+ 1-723, Pls. 1–3.

1993. Oncorhynchus mykiss : Stearley, R.F. and Smith, G.R.:

Trans. Am. Fish. Soc. 122 (1): 21.

Picture courtesy Bagra et al., 2009

Common name: Rainbow trout.

Materials examined: 5 ex., Poma River , Ramghat, Papumpare district, RGUMF-0166, 26°57’38’’ N 93°24’26’’ E 129, Alt.129 msl .

Distribution: The native range of the fish is the Eastern Pacific Ocean and the freshwater, mainly west of the Rocky Mountains, from northwest Mexico, to the Kuskokwim River, Alaska (MacCrimmon 1971). Currently the rainbow trout has been widely introduced into suitable environments throughout the United States and around the world. Many of these introductions have established wild, self-sustaining populations ( Fuller et al., 1999).

Remarks: Oncorhynchus mykiss are primarily freshwater fish, although sea-run populations, often known as steelhead, exist in some areas. The species has been introduced worldwide because of its flexibility and adaptability to new habitats, including hatcheries, lakes, rivers, ponds, and artificial impoundments. Few considerations seem to limit its distribution; however, successful spawning in rivers in Europe is uncommon as per NOBANIS -Invasive Alien Species Fact Sheet. Studies have been done on the capability of natural hybridization with native species ( Hitt et al., 2003; Boyer, et al., 2008; Corsi et al., 2013) and found that it leads to the eradication of local species and threatened with genomic extinction. The species has also been included in the Global Invasive Species Database (2019) because of its ability of hybridisation, disease transmission, predation and competition with native species. As per the database, some species, have become virtually extinct because of this and also some other native fish also affected by hybridization with the species in many countries.

Salmo gairdnerii , that have been introduced to India in the year 1907 from Sri Lanka and Germany has been synonymized to Oncorhynchus mykiss , and the former retain as a valid name. Five juvenile specimens of Rainbow trout were reported from Poma River near Ramghat by Bagra et al. (2009). The place where this fish was caught was near the border of Assam Arunachal Pradesh , where the Rheophilic Poma River just enter the plains of Assam with a different name, Boroi River ( Figure 1 ). Getting juveniles of the species in a different river system at Ramghat , Poma River , and far away from place of their actual stocking ie, Tawang district of the state is scientifically inexplicable and will seriously rise an issue if the fish has really established in the natural water bodies of the state. Very recently an adult fish of the species has been collected by the author from a natural stream named Dhinikho river from Shergaon village, which is anticipated since there is a government trout hatchery nearby .

Figures

Figure 1. Map of Arunachal Pradesh showing different sites where the exotic salmon are reported.