Big golden mahseer to small kudremukh barb, freshwater fish are richly diverse

News: In this article, Vidhyadhar Atkore while speaking to Times Evoke explained the river biodiversity and threat faced by it due to human interference. He has studied four major river basins, the Malaprabha, Mhadei, Tunga and Bhadra systems in Karnataka.

What are some significant findings?

One, the free-flowing riverine systems have nearly 50% more endemic fish species, compared to hydrologically modified systems which have more generalist species found across diverse habitats. For instance, the Tunga and Bhadra riverine structures are free-flowing, Mhadei and Malaprabha are highly disturbed in terms of the number of check dams built on them, the quality of the water, the degradation of vegetation along the river banks, etc.

Two, endemic and habitat specialist fish require certain conditions, like an ambient temperature, vegetation, etc.  to survive. They can only find these in areas without disturbance or no check dams, water diversions and fishing pressure.

Three, dams act as a barrier and stand in the way of fish. It also impacts the composition of species found naturally. Mhadei and Malaprabha have many barrages leading to changes in water flow. Also, when the flow is disturbed by human activity, surface-dwelling fish are affected.

Four, human modifications of hydrology have enormous impacts on river sediments, vegetation and water surfaces. There are more insectivore species living in the Tunga and Bhadra regions due to more insects while the modified sites have more omnivorous and carnivorous fish.

Five, an entirely new fish was discovered which was named as Kudremukh barb. It swims along in the headwaters of the Tunga. Taxonomically, it is named as Pethia striata. It has remarkable colour, the male is in shaded red and the female is of grey color with unique cross-stripe pattern.

Why there is need of more research in the field of riverine ecosystem?

First, there is need to know the causes and consequences of the degradation of freshwater systems, due to anthropogenic pressures like illegal fishing, sand mining, hydropower dams, etc.

Second, the baseline data is essential to deepen the understanding of river biodiversity. Also, there is comparatively less ecological information on riverine systems. For example, the golden mahseer, a freshwater fish which is migratory in nature can weigh up to 55 kgs, but it is hard to find a fish of that size now.

Third, freshwater riverine systems are linked to human wellbeing. Hence, there is need to read more about freshwater biodiversity to appreciate the huge variations of species, their extraordinary colours, abilities and migratory behaviour. It will also help in inspiring people to join campaigns for river cleaning.

What is the way forward?

First, mitigations can help species. For instance, retaining undammed tributaries enables fish to recover.

Second, minimize plastic usage because it is a major threat which is affecting freshwater systems. Also, the removal of obsolete dams which is taking place worldwide to save freshwater species should be considered now.

Third, those who buy ornamental fish should not release them into streams. Because, this adversely impacts native fish.

Source: This post is based on the article “Big golden mahseer to small kudremukh barb, freshwater fish are richly diverse” published in Times of India on 12^th Feb 2022.