Farmers have suffered significant losses from the massive death of clams in recent years. The Fisheries Research Institute has thus developed a type of probiotics - Bacillus pumilus D5 that is resistant to aquatic pathogens and improves water quality. Probiotics that support the proper culture management of clam famers and improve the breeding environment can also effectively enhance the growth and survival rates of clams.
The Fisheries Research Institute has noted the large number of clam deaths in Taiwan clam farming since the 1970s. In earlier years, unexplainable seasonal deaths occurred mainly in March, June, and September each year, but non-seasonal deaths are now occurring more frequently, not only causing losses to farmers, but also resulting in a serious impact to the national economy. It is speculated that the deaths of large numbers of clams are caused by many factors such as rapid changes in the breeding culture’s environmental temperature and salinity, deterioration of water quality and the benthic environment, excessively high culture density, and improper management of the culture. The Fisheries Research Institute isolated a probiotic-Bacillus pumilus D5 from the intestine of white shrimp in 2015. The test showed that adding Bacillus pumilus D5 to the feed of clams for 6 months can increase their growth, greatly cut down the number of Vibrio in the culture pond water, effectively reduce the concentration of total toxic ammonia nitrogen and hydrogen sulfide in the pond, regulate the immunity of the clams, and improve their survival rate.
According to the field survey of clam farming in Yunlin, Chiayi, and Tainan areas from 2015 to 2018, Fisheries Research Institute pointed out that there were about 129 incidents of clam deaths in 255 clam farm pond surveys due to just poor water quality, accounting for 50%; about 100 incidents of clam deaths resulted from poor water quality combined with Vibrio or Gram-negative bacteria infection, accounting for about 40%. It is inferred that poor water quality caused by improper breeding management is the biggest cause of clam deaths, and the secondary cause is poor water quality combined with Vibrio or Gram-negative bacteria mixed infection. A test of a Vibrio vulnificus attack on clams in the laboratory showed that Vibrio vulnificus and V. brasiliensis can result in their death, while V. anguillarum and V. parahaemolyticus can result in their weakness.
As poor water quality and Vibrio infection are important causes of clam deaths, the Fisheries Research Institute reported that it has transferred the technology of Bacillus pumilus D5 with anti-Vibrio and water quality improvement capabilities to 5 probiotic manufacturers and will match it with other probiotics in the future for the use in bait and feed, which can effectively reduce the amount of Vibrio in clam ponds and improve water quality. In combination with strengthening farmers’ management of clam cultures, the probiotic is expected to effectively solve the problems faced by Taiwan’s clam industry, restore the production of clams, and allow consumers to enjoy clams of excellent quality at reasonable prices.
Aquaculture Division, Fisheries Research Institute
Figure. Inhibition of the pathogen Vibrio harveyi by Bacillus pumilus D5.