Reintroduction of Himalayan Snow Trout to Naini Lake: A Milestone for Uttarakhand’s Aquatic Conservation
Why in the News?
In April 2026, scientists from the Department of Zoology at the DSB Campus of Kumaun University, Nainital, successfully reintroduced the Himalayan Snow Trout (locally called Asela) into Naini Lake after an absence of nearly three decades.
This landmark conservation initiative marks a major ecological breakthrough, providing clear evidence that restoration and water quality improvement efforts at Naini Lake over the last two decades are yielding positive results.
About the Himalayan Snow Trout
- Scientific Name: Schizothorax richardsonii
- Local Name: Asela or “Himalaya ki Macchli”
- Geographical Range: It is a primitive cold-water fish species native to high-altitude Himalayan rivers and lakes, distributed across Jammu & Kashmir, Himachal Pradesh, Uttarakhand, and North-East India. It co-evolved with the formation of the Himalayas.
- Ecological Status: * IUCN Red List Status:Vulnerable (due to habitat fragmentation, damming, climate change, and overexploitation).
- Ecological Indicator: It acts as a keystone species and an environmental health indicator for Himalayan aquatic systems due to its high sensitivity to pollution and low dissolved oxygen levels.
Why Did the Species Vanish from Naini Lake?
Up until the 1990s, Snow Trout was a dominant native species in the Kumaon lakes (Naini, Bhimtal, Sattal). However, it completely disappeared from Naini Lake due to several anthropogenic and environmental factors:
- Severe Eutrophication: High influx of municipal sewage, urban runoff, and tourism-related waste led to excessive nutrient loading, causing dense algal blooms.
- Depletion of Dissolved Oxygen: The decomposition of algal blooms caused oxygen levels in the mid-to-lower layers of the 28-meter-deep lake to plummet to near-zero levels.
- Invasive Species Competition: The introduction of exotic, aggressive fish species (like the Brown Trout and Common Carp) outcompeted the sensitive native Snow Trout for food and sub-optimal habitat spaces.
The Scientific Breakthrough: Lab to Lake Reintroduction
The revival project was executed under the leadership of Prof. Harish Chandra Singh Bisht at Kumaun University.
- Aquaculture Technologies: Scientists successfully bred and raised around 300 Snow Trout fingerlings in lab settings using advanced Biofloc Technology Centre and Recirculating Aquaculture Systems (RAS). Biofloc technology uses beneficial microbial clusters to maintain water quality and recycle waste into protein-rich fish food.
- Controlled Adaptation: The fingerlings were released into specialized protective cages submerged in the lake, strategically placed near the lake’s bottom aeration zones. This ensures the young fish can safely acclimatize to the natural lake environment without immediate threat from predators.
Ecological and Environmental Significance
The reintroduction of Asela is expected to significantly accelerate the self-purification and ecological stabilization of Naini Lake:
- Natural Biological Control: Snow Trout feed directly on algae, moss, and detritus. Their presence will naturally restrict excessive algal blooms and bio-fouling, thereby maintaining pristine water clarity.
- Restoration of Food Chain: Reintroducing a native keystone species corrects the ecological imbalance created by invasive fish species over the last 30 years.
- Proof of Concept for Lake Restoration: The survival of these sensitive fish confirms that artificial aeration grids (installed at the lakebed to inject oxygen) and desilting drives have successfully minimized toxic chemical loads like nitrates and phosphates.
Key Prelims-Oriented Facts about Naini Lake
- Origin & Geography: It is a natural freshwater lake of tectonic origin, shaped like a crescent or kidney, situated in the heart of Nainital.
- Scriptural Mention: In the Skanda Purana, Naini Lake is referred to as Tri-Rishi-Sarovar (associated with Sages Atri, Pulastya, and Pulaha).
- Primary Feeder: Balia Nala is the primary natural feeder stream of Naini Lake.
- Unique Feature: The bridge at the southern end (Tallital) houses the world’s only post office located on a lake bridge.