The overall goal of the Bivalve Hatchery Health Consortium (BHHC) is to aid the bivalve aquaculture industry in the United States coast by assessing potential causes to hatchery run crashes along with providing suggestions for methods to manage these crashes. In recent years, there has been a major increase in larval crashes in these hatcheries, however, what is causing these crashes is not well known.
The BHHC collected incoming water (before water treatment), larval tank water, and larval samples from production runs experiencing unusual losses (unhealthy), as well as from normal (healthy) runs. Larvae from the healthy and unhealthy runs were washed in filtered sterile artificial seawater (FSSW) and incubated overnight in FSSW to allow pathogens in the larvae to shed (shed water). Incoming, tank, and shed water were size fractionated (Figure 1) to eliminate potential pathogens based on size. Healthy larvae (5-10 days post fertilization) were exposed to FSSW (negative control), the non-fractionated water (positive control), and the 0.22 micron-filtered water (eliminating bacteria and parasites, retaining viruses and toxins).
The relative percent survival (RPS) of larvae exposed to fractionated water compared to survival of larvae exposed to FSSW was calculated after 20 hours of exposure. Preliminary results showing mortality of healthy larvae exposed to 0.22 micron filtered water from some of the hatcheries indicate that crashes may be due to incoming water quality issues, toxins, or viruses (Table. 2). Additionally, as a year-round alternative to the larval assay, we are developing a less labor intensive and faster water screening assay utilizing hemocytes from adult bivalves. Results from these assays and other diagnostic tests are shared with the hatcheries along with a document of suggested issues and changes to be applied to their next hatchery run. The BHHC has been set to continue another year of sampling runs during the 2025 production season.