Yellow rasbora (Rasbora lateristriata), known as Wader fish in Indonesia, is classified as vulnerable by the International Union for Conservation of Nature Red List of Threatened Species, and its status can escalate to critical if its habitat continues to decline drastically, according to Dr. Djumanto in his inaugural professorial speech on Tuesday (9/5).
The newly inaugurated professor of aquatic resources management added that several factors with very high levels and diverse types threatened freshwater fish native to inland waters, including the yellow rasbora.
One of the threats is environmentally harmful fishing methods using destructive fishing gear such as stun or electric shock. Some irresponsible anglers and fish enthusiasts also release certain species that reduce the prey fish population. In addition, invasive foreign species can become competitors or predators of native fish.
According to the professor, inland waters in Yogyakarta still hold 47 species of fish, including 42 species of local/native fish and five species of introduced fish, namely red devil cichlid, guppies, tilapia, suckermouth catfish, and swordtails. Based on their status, 83% of the fish species are low-risk, 13% have yet to be evaluated, and 2% require further data and are vulnerable.
“Vulnerable fish such as yellow rasbora can become critical when their habitat deteriorates, rendering them unable to reproduce. Likewise, fish with low-risk status can become vulnerable if fishing and other anthropogenic disturbances are very high,” he explained.
Several ways to protect and preserve native fish, Professor Djumanto said, were by controlled fish utilization, marine reserve, restocking, invasive fish control, domestication of native fish, and spawning habitat modification.
According to him, most fish spawn during the rainy season when water is abundant and of good quality. In yellow rasbora inhabiting the Ngrancah River, spawning occurs between the rainy and dry seasons when air temperatures are low and oxygen is high.
Creating basins of about 2×1 square meters and an average water depth of 30 cm with a sandy bottom substrate on the riverbank can trigger yellow rasbora to come and spawn. The more basins along the side of the river, the more likely they are to breed, resulting in a high population. The exact mode can be used for other species targeted for conservation, such as barred loach (Nemacheilus fasciatus).
Concluding his speech, he emphasized the need to increase the diversity of inland water fish resources through various efforts, which can involve the community through education, competitions, or tourism-themed activities. Invasive fish control can be done by educating and preventing the spread of invasive fish in public waters.