Infection and mortality by
the yeast Metschnikowia bicuspidata var. bicuspidata in
chinook salmon fed live adult brine shrimp (Artemia franciscana)
M.M. Moore, M.S. Strom-2003
Aquaculture, 220(1-4): 43-57
Abstract:
First-feeding chinook salmon were fed either live
adult Artemia franciscana or commercial feed over a 15-week period.
Unexplained mortality began occurring in the Artemia-fed fish after
35 days on the diets, with cumulative mortality reaching 34.5% in the Artemia-fed
fish compared with 4.3% in feed-fed fish. Necropsy examinations revealed
systemic fungal yeast infections and the causative agent was cultured from
kidneys. Fungal cells were observed in the transport water of Artemia
shipments and within the Artemia. The Artemia were purchased
from a retail supplier, and originated from salt ponds in San Francisco Bay
(SFB), California. Artemia infection rates ranged from 0.5% to 37.5%
(mean 16.5±3.59%) in shipments received over a 5-week period. The fungus
was characterized by morphological and physiological properties and was
identified as Metschnikowia sp., a pathogenic yeast of aquatic
invertebrates. The yeast grew at 9–27 °C, and 0–180 ppt NaCl, and could
tolerate salinity of at least 270 ppt. Sequence analysis of the divergent
D1/D2 domain of ascomycetous yeast 26S ribosomal DNA identified the organism
as Metschnikowia bicuspidata var. bicuspidata. The organism
was found in water from the salt ponds and probably entered from the bay.
Mortality due to the fungal infection stopped after changes were made in the
handling of incoming Artemia shipments.
(Resource Enhancement and Utilization Technologies
Division, Northwest Fisheries Science Center, National Marine Fisheries
Service, National Oceanic and Atmospheric Administration, 2725 Montlake
Boulevard East, Seattle, WA 98112-2097, USA, e-mail of M.S. Strom: mark.strom@noaa.gov)