Small-scale freshwater fish farming is becoming increasingly popular among residents of Petung Hamlet in Wates Village, Magelang Regency, Central Java. Locals have taken advantage of the area’s abundant water resources to establish fish farms, which serve as an additional source of income to enhance their household economies. However, this venture is not without its challenges, as farmers often suffer losses due to tPond ManagementPond Managementhe sudden deaths of large numbers of fish.
“We have many human resources here, but we still lack the skills to deal with these fish diseases,” said Winarno, one of the residents, along with several fish farmers, during an outreach activity held by lecturers from the Department of Pathology, Faculty of Veterinary Medicine, Universitas Gadjah Mada (FKH UGM).
During the field visit, many fish farmers shared issues they commonly encounter, including sudden fish deaths, fungal and parasitic infections on fish scales, and pond management problems.
According to veterinarian Sugiyono, many farmers in Petung Hamlet tend to release fish fry directly into ponds after purchasing them from the market, a habit that often causes stress and makes the fish more susceptible to disease.
“This habit is the main cause of fry mortality,” said Sugiyono on Monday, Oct. 20, 2025.
He explained that proper pond management begins with acclimating newly purchased fish.
The fish should first be left in their original container, then placed in a new container filled with water at room temperature.
After that, they should be transferred to a container containing pond water mixed with medication or coarse salt to eliminate pathogens.
“Once the water is properly prepared, the fry can safely be released into the main pond,” he added.
Agreeing with this, Mia Nur Farida, another lecturer from FKH UGM, emphasized that sudden changes in water conditions can weaken the fish’s immune system, making them more susceptible to fungal and bacterial infections.
Proper pond and water preparation, she said, is crucial for successful aquaculture.
“Fish are susceptible to stress; if they don’t get sick, they might die, and mass mortality is quite common,” stressed Farida.
In addition to newly purchased fry, farmers also reported mass deaths among gourami, which suddenly changed color before dying.
Sugiyono explained that this phenomenon is related to hypoxia, or lack of oxygen in the pond water.
During the rainy season, the photosynthesis rate of algae decreases, reducing oxygen levels, especially in densely populated ponds.
To prevent this, Sugiyono recommended changing the water regularly or using aerators, as well as reducing fish density by dividing the fish among several ponds.
“As the fish grow larger, they should be separated into different ponds,” he advised.
Fungal and parasitic infections are also common problems.
Afif Muhammad Akrom explained that fungi naturally exist in aquatic environments.
“However, fungal infections only occur when fish are stressed, have weakened immunity, or suffer wounds on their bodies,” he explained.
According to Akrom, these wounds often occur when fish are transferred from paddy fields to ponds or during fighting.
Fungal growth typically appears on the skin, scales, or gills.
“Weather conditions or contaminated water sources can trigger this disease, and fungal treatment can be quite challenging,” he added.
Sugiyono suggested using antifungal medications available on the market to treat infections. He also recommended adding coarse salt and maintaining proper water circulation to suppress fungal growth.
“Fungi generally thrive in cold water and shaded ponds, so ponds should receive enough sunlight,” he explained.
Furthermore, Farida discussed the danger of Argulus parasites, also known as fish lice, which often attach to scales or gills.
These parasites make it difficult for fish to breathe, as indicated by their rapid swimming and frequent collisions with pond walls.
“The wounds they cause allow bacteria to enter the fish’s body,” said Farida.
She added that Argulus larvae do not immediately attach to fish after hatching but first develop on pond walls or aquatic plants.
“That’s why maintaining pond cleanliness is essential. Even if the fish appear clean, parasite eggs might still be hiding,” she warned.
According to Sugiyono, these parasites are difficult to eliminate using medication.
Even when immersed in formalin, Argulus only becomes weakened, not dying.
The best prevention, he said, is to use a biofilter system to filter water and prevent larvae and parasites from entering the pond.
He emphasized the importance of regularly replacing water and drying the pond after harvest to kill any remaining bacteria or parasites.
“After drying, the soil should be treated and enriched with compost to promote the growth of natural plankton as food for new fish,” he explained.
For new ponds, he advised drying the pond after excavation to remove toxic gases from the mud.
“Two weeks is enough before filling the pond with water and fry, once plankton growth has begun,” said Sugiyono.
In contrast, Akrom noted that for cement ponds, the waiting period is shorter, about one week, before the pond should be drained again to allow moss to grow.
“Alternatively, you can release small cethol fish for three to five days before adding the fry,” he concluded.
Closing the activity, Farida, as the team leader, expressed hope that the program would help improve the productivity of local fish farmers and strengthen their economic resilience.
“We hope this program will empower fish farmers to continue developing their productivity and economic capacity,” she said.
Author: Hanifah
Editor: Gusti Grehenson
Post-editor: Lintang Andwyna
Photographs: Jesi and Freepik