Under the opaque, gently-rippled waters of the Sukhna lake, lurk treasures of biodiversity. Six new species of fish have been documented at the Sukhna by the department of zoology, Panjab University, which were not found in the fish biodiversity project of 2005-2006 and carp morphometric survey of 2012-2014.

The addition was revealed by a report — Evaluation of Fish Biodiversity in Sukhna lake for Sustainable Aquaculture Practices — prepared by the department and submitted to the chief conservator of forests and wildlife, Chandigarh. The new species found during the evaluation of 2025-2026 were mola, shark catfish, Amazonian suckermouth/sailfin catfish, Nile tilapia, goldfish and barred spiny eel.

In the assessments of 2005-2006 and 2012-2014, 32 and 19 fish species were recorded respectively. In the latest evaluation, 25 species of fish were detected from 289 samples. Of these, two species (lanchi and mirror carp) are listed as ‘vulnerable’ and one (silver carp) as ‘near threatened’ by the International Union for Conservation of Nature (IUCN). The maximum specimens, 93, were from one species, kalbasu. The fish samples were dominated numerically by five species, including the kalbasu, from the Cyprinidae family.

The evaluation of fish biodiversity commenced in October 2025 and is scheduled for another round of sampling in October 2026. Two attempts at sampling this month at the Sukhna lake, on October 8 and 15, had to be called off due to wind turbulence and rain, respectively.

“We employed three methods to sample fish. At four points on the northern shores, gillnets were cast to trap fish. The nets were cast into the water for one hour, the catch was recovered after that, and the fish were photographed, documented and then released back into the water to avoid mortality during sampling. On the southern bank, we sampled fish from seven points used by recreational anglers, and these yielded the maximum diversity of fish species and the best growth parameters. A record of a new species (barred spiny eel) was procured from Dr Manjit Singh, who photographed an eel in the bill of a great cormorant,” associate professor Dr Ravneet Kaur, who is the principal investigator for the evaluation, told this writer. The project co-investigator is Dr Ashwani Kumar, joint director, animal husbandry and fisheries, Chandigarh. Kaur was assisted by research scholars Muskan Jain, Khushdeep Kaur, Chhavi Chawla, Ashita Sharma and Neha Dhiman.

The latest evaluation takes a step forward from the earlier fish surveys at the Sukhna by introducing baseline data for fish densities and bacterial presence in the gills and skin of fishes. The fish density recorded for the catch in the gillnets was calculated at a healthy Catch Per Unit Effort (CPUE) of 9.4 and 13.4 fish/net/hour over two sampling days. “The fish samples showed signs of good growth,” said Kaur.

Microbiological examination of nine fish samples confirmed the presence of bacteria in three specimens: Aeromonas veronii bacteria on the skin of a magur catfish and Nile tilapia, while a Pseudomonas genus of bacteria was detected on the skin of a rohu fish. “It is important to continue disease surveillance and deepen studies of bacteria afflicting the Sukhna fish because bacteria can turn resistant and enter the human food chain,” added Kaur.

Of the 25 species recorded in the evaluation, eight were exotic (common, silver, mirror, bighead and grass carps along with goldfish, Amazonian catfish and Nile tilapia). Of concern was the thoughtless and illegal dumping of exotic aquarium fish in the Sukhna (posing a threat to native species), as evidenced by recovered specimens of goldfish, Amazonian catfish and Nile tilapia.

Ramsar criterion: The lake was recently inducted in the Ramsar List of Wetlands of International Importance under the classification of a “peri-urban reservoir”. Delving into Sukhna’s importance for fish biodiversity during adverse periods, the official Ramsar Information Sheet (RIS) published on October 15, 2026, stated that certain fish species “utilise the Sukhna wetland (Ramsar Site 2602) as a critical refuge habitat during periods of hydrological fluctuations, elevated temperatures and reduced flow conditions”.

“The wetland also supports the seasonal movement and migration of fish assemblages from adjoining upstream inlets and ephemeral drainage channels during dry periods. Shallow littoral zones, emergent vegetation and marsh interfaces provide important spawning, nursery, foraging and shelter habitats, while also reducing predation pressure and supporting juvenile recruitment and survival during ecologically stressful conditions,” the RIS stated.