From the results of water sample analysis of lobster farming areas, sediment, and lobsters, Institute III reported that the water quality of the lobster farming areas in the monitoring period, assessed by the Air Quality Index (AWQI), was mostly good to very good, except for the Xuân Yên farming area, Sông Cầu town (Phú Yên) and Xuân Tự, Vạn Ninh district (Khánh Hòa) which were poor (AWQI = 36 – 38).
Accordingly, Lạch Cổ Cò area (Vạn Thạnh, Khánh Hòa) had a density of pathogenic bacteria (Vibrio spp.) exceeding the permissible limit; Xuân Tự area (Vạn Hưng) had poor water quality, temperature, and N-NH4+ content exceeding the permissible limits, and low dissolved oxygen concentration in the water.
In addition, the causative agent of milky disease monitored in cultured lobsters in Xuân Phương, Xuân Yên, and Lạch Cổ Cò accounted for 16.7%. The bacteria that cause red body disease in lobsters in Xuân Phương, Xuân Yên accounted for 33.3% (2/6 samples in each area), and in Lạch Cổ Cò accounted for 50% (3/6 samples).
Mass death of lobsters caused great damage to farmers in Khánh Hòa.
The dissolved oxygen content at the nearshore locations of the farming areas of Xuân Thành, Xuân Phương, Xuân Tự, and Bình Ba; the nearshore locations and the farming area of Xuân Yên were lower than the permissible limits. The results of sediment sample analysis showed that most of the environmental parameters increased compared to the monitoring period in February 2024, in addition, the bottom surface of the farming areas had a lot of snail, clam, and oyster shells.
According to the forecast, in the coming time, the weather in Phú Yên and Khánh Hòa provinces will have showers and thunderstorms in the late afternoon and at night, sunny during the day, and sometimes severe heat (Phú Yên). Therefore, the aquatic environment will change, affecting the development of lobsters.
Institute III recommends that farmers lower their cages to an appropriate water level and at the same time increase the shading of the cages/rafts with shade nets to reduce the impact of temperature on the health of farmed lobsters.
Farmers should hang lime bags around the cages/rafts (about 2kg of lime/bag) to limit the high density of pathogenic bacteria in all farming areas and the nearshore areas of Xuân Thành (Sông Cầu town), Lạch Cổ Cò, and Xuân Tự (Vạn Ninh).
Farmers need to reduce the lobster density in the cages to suit each stage of lobster farming, clean the cage nets, collect leftover food after each feeding of the lobsters, and maintain a distance between the rafts to create good ventilation, increase water exchange inside and outside the farming cages, reduce the N-NH4+ content, and reduce the consumption of dissolved oxygen in the water (N-NH4+ exceeded the permissible limit by 1.2-2 times in the farming areas of Xuân Yên, Xuân Tự, and the nearshore areas of Xuân Phương, Xuân Thành). In addition, Institute III recommends that people prepare aerators and oxygen cylinders in case of suffocation of farmed lobsters due to locally low dissolved oxygen.
Previously, hundreds of lobster farming households in Khánh Hòa were surprised when they discovered that the lobsters had died in large numbers. The lobsters all showed symptoms of a pink-white belly, reduced appetite or stopped eating, lethargy, slowness, and weakness, then died.
