Welcome to the Indian edition of our migratory fish blog post series. I am Sayali and I have been working as a research assistant for FIRElab since November 2018. I am passionate about restoring river paths to protect our freshwater fish species and rebuild connections in river systems so that our fish can swim freely.
My earliest memory of migratory fish would be fishing for small fish with my uncles in my native village in Konkan, India where we would pick the small, slimey, tiny, snake like fish with our hands. At the time, I didn’t know that those small fish were eels, a migratory fish with whom I have developed a recent connection through my research.
With FIRELab, I am leading an expert elicitation to understand the passability of European eels (Anguilla Anguilla) through different instream infrastructure such as dams, weirs, and road culverts. I’ll be sharing more updates on this in a future blogpost – hopefully once my first peer-reviewed manuscript is accepted! However, today I am going to focus on India, and fun facts on the Indian Motted Eel (Anguilla bengalensis). So, let’s get started.
Fishes in India’s rivers generally migrate for three major events: wintering, feeding, and spawning. Hilsa Shad (Tenualosa ilisha) is the most popular anadromous fish species (migrating up rivers from the sea to spawn) in India, and ascends the longest distance in the rivers of both eastern and western India, including the Ganges river system from the sea for breeding (Dass and Hassan, 2008). It is a very popular and sought-after food fish in the Indian subcontinent. A noteworthy catadromous species is the Indian Mottled Eel (Anguilla bengalensis), which spends most of its life in fresh waters and migrates to sea to spawn.
Indian Mottled Eel range expands from East Africa rivers and coastal areas across the Indian Ocean to mainland India, Pakistan, Bangladesh, Indonesia and Malaysia, and is an occasional visitor to the Arabian Peninsula. Indian Mottled Eels inhabit various niches in river systems, their habitat expands from, quiet, undisturbed areas containing mud substrate to deep water, fast-flowing rock pools of rivers (Bell-Cross and Minshull 1988). Within the IUCN Habitat Classification Scheme table, most of the listed habitats are considered important for eels.
Indian Mottled Eels have a very interesting life cycle. At each stage, their bodies have characteristic shapes and sizes. The leaf-shaped marine larval stage is referred to as leptocephalus; then as glass eels when they reach the continental waters (Mondal, 2019). They then develop into pigmented elvers and eventually into yellow eels. The final stage of the life cycle is the marine-migratory silver eel, characterised by silvery countershading on the fish body and large eyes (Pantulu,1957). Silver eels usually migrate downstream from the months of April to September.
Like all anguillids, Indian Mottled Eels are semelparous, meaning, they spawn only once before death. These traits arguably increase the impact of threats to the species, exposing them to human-induced pressures in both freshwater and marine environments such as barriers to migration, river pollution, habitat degradation, climate change, and unsustainable exploitation. However, we have a limited understanding about human-induced pressures on this species, especially river obstructions and over harvesting in India and Bangladesh.
Thanks for reading and stay tuned for our next post in two weeks!
Bell-Cross, G. and Minshull, J.L. 1988. The fishes of Zimbabwe. National Museums and Monuments of Zimbabwe.
Dass, M. and Hassan M.A., 2008. The status of fish migration and passes with a special reference to India. CIFRU
Mondal, A., 2019. Indian Mottled Freshwater Eel, Anguilla bengalensis Bengalensis (Gray, 1831), A Threatened Species of Indian Subcontinent- A Review. International Journal of Oceanography & Aquaculture, 3(1).
Pantulu, V.R. 1957. Studies on the biology of the Indian freshwater eel, Anguilla bengalensis, Gray. Proceedings of the National Institute of Sciences of India 22(5): 259-280.