Disease Management for Hawaiian Aquaculture |
The overall goal of this project is to develop management strategies to minimize losses from diseases at aquaculture farms in Hawaii. Specific objectives related to that goal were to:
This project focuses on problems that directly affect production of Hawaii aquaculture crops and provides disease screening for other CTSA-funded projects. These efforts will improve production of Hawaii aquaculture facilities or procure new information that will lead to improved health management strategies and increased aquaculture productivity in Hawaii.
Diagnostic support services to the developing ornamental fish culture industry will help producers to identify causes of diseases in ornamental species.
Probiotics are an emerging means of controlling bacterial problems in shrimp hatcheries. A procedures manual for implementing a probiotic program in a shrimp hatchery is not currently available. Developing such a manual will be produce a useful tool for shrimp farmers.
Objective: Work on the development of practical, on-farm measures to mitigate the impact of Taura syndrome on penaeid shrimp farming.
After a shrimp farm in Kahuku, Hawaii, was devastated by Taura Syndrome (TS) in 1995, it stocked and cultured Penaeus stylirostris, which is resistant to the disease.
Since Spring 1995, no active cases of TS have been found in shrimp cultured on Kahuku farms. In 1996, the farms resumed stocking juvenile Penaeus vannamei at high density-300 to 500 shrimp per cubic meter-in growout raceways at the farm previously devastated by TS. No new cases of TS occurred on this farm although all the raceways were stocked with P. vannamei and harvested through several cycles.
Investigators continue to monitor the "at risk" shrimp farms. investigators processed more than 60 case submissions and examined Shrimp collected from the farm in 36 case submissions and examined by histopathology did not show the presence of TS lesions. Therefore, findings from the ongoing monitoring support the conclusion that TSV was eradicated during the period of Penaeus stylirostris culture on the farm.
Objective: Field test an approach for IHHNV decontamination of shrimp ponds.
Investigators conducted several trials to measure the effect of solar heating on the surface temperature of soil. Soil surface temperatures were recorded at 64° to 66° C for one to two hours in the afternoon in soils exposed to direct sunlight. Because these temperatures are high enough to inactivate the known penaeid shrimp viruses, solar heating should be considered as a practical means to disinfect shrimp pond bottoms.
Objective: Monitor the effectiveness of IHHNV decontamination on a shrimp farm in Hawaii.
With CTSA support, investigators were able to help develop a best management strategy for operation of a Kahuku farm at which IHHNV is known to be endemic. Investigators processed 24 case submissions with roughly 350 shrimp from that Kahuku farm. Histopathology and gene probe methods were used for virus detection, and the obligate pathogen IHHN was detected in one shrimp specimen sampled from the growout area of the farm. This was anticipated because the growout facility did not undergo system-wide decontamination and is considered to be contaminated with IHHNV. However, IHHNV was not detected in any of the broodstock, larval or post-larval samples evaluated. These findings support the conclusion that reproduction and larval rearing facilities remain free of IHHNV following the partial decontamination steps implemented in September 1996.
Objective: Assess the infectivity of IHHN virus in feces after passage through the digestive tract of a species of water bird.
Three trials were conducted in which IHHNV-infected shrimp carcasses were fed to two night herons obtained for the avian vector study. Two of three feces samples collected within 24 hours after the birds ingested the shrimp were positive for IHHNV by the PCR method. Fecal samples collected on subsequent days were negative for IHHNV by the PCR method. In addition, a trial was conducted to assess whether the tilapia RLO organism could be transmitted in bird feces to susceptible tilapia.
Known RLO-infected dying tilapia were fed to the avian vector over five consecutive days. Each day the feces on the plastic sheet covering the bottom of the bird cage were collected and added to the water in a tank containing juvenile, RLO-free tilapia. Thirty days following addition of bird feces neither clinical, gross pathological or histological signs of RLO disease were found in the exposed or the unexposed control groups of tilapia. Survival was 95 to 100 percent in both groups of fish. These findings indicate that the Hawaiian tilapia RLO does not appear to survive in an infectious form in feces after passage through an avian digestive tract.
Objective: Test the susceptibility of the endemic caridean shrimp, Halocaridina rubra, to infection and disease by the penaeid shrimp viruses IHHN and the newly discovered Taura Syndrome virus (TSV).
Work was conducted on two fronts. The first continued studies on birds as vectors of shrimp viruses. The second front tested H. rubra as a possible reservoir host for IHHN and TSV.
A colony of about 100 H. rubra was established in a 300-gallon holding tank in the isolation area at AFRC. The population of H. rubra were provided by Dr. Richard Brock, who collected the animals from a coastal pond in Kona, Hawaii. Virus challenge bioassay trials with H. rubra began in December 1996. The results indicate that H. rubra is not susceptible to disease from either IHHNV or TSV and does not serve as a reservoir host for IHHNV.
Objective: Produce an operation manual for application of the probiotic technology for shrimp hatcheries in Hawaii.
During year four, information was gathered on procedures used for probiotic application at two commercial shrimp hatcheries in Central and South America.
Objective: Test the efficacy of hydrogen peroxide to control common ectoparasite infestation of cultured fishes.
Work continued to test hydrogen peroxide, which the Food and Drug Administration (FDA) has classified as a low regulatory priority compound for aquaculture, as a chemical control agent for treatment of common ectoparasite infestation of cultured freshwater and marine fish. During this reporting period, 26 juvenile mo`i (Polydactylus sexfilis) with Amyloodinium sp. infection of the gills were treated with hydrogen peroxide to determine the fish's tolerance to hydrogen peroxide (e.g. concentration and duration) and to test the compound's efficacy as a chemical control of Amyloodinium sp. Juvenile mo`i were found to tolerate exposure to hydrogen peroxide at 150 ppm for 30 to 60 minutes. Thirteen fish were treated with hydrogen peroxide and 13 were untreated control fish. Gill wet-mounts of the treated juvenile mo`i showed significantly reduced numbers of Amyloodinium sp., which indicates that hydrogen peroxide may be an effective treatment for ectoparasite disease caused by Amyloodinium sp.
During the coming months, investigators plan to: