The sea louse (Lepeophtheirus salmonis), whose larvae are planktonic and
disseminated in the water column, is an economically important parasite of Atlantic
salmon (Salmo Salar). The effect of temperature (5, 10, 15°C), diet (larvae alone, larvae
plus phytoplankton), and bivalve size (small, medium, large) on the amount of L.
salmonis larvae ingested by various species of filter-feeding bivalves (Pacific oysters,
Pacific scallops, blue/Gallo’s mussel hybrids, basket cockles) was examined in a series of
laboratory experiments. Four separate temperature/diet experiments were conducted (one
for each species) in which large bivalves were individually placed in 2-L containers
holding 750 ml of aerated, filtered seawater and fed one of three treatment diets: (1)
phytoplankton: ~7.1 x 104 cells ml-1 of Isochrysis sp. (Tahitian strain, TISO); (2) sea lice
larvae: ~431 larvae (mostly nauplii); and (3) phytoplankton and larvae (at the levels
mentioned above). There was also a control treatment of phytoplankton and larvae, but
no bivalve. After feeding for 1 h, the bivalve soft tissues were excised and preserved, the
digestive system was dissected, and sea lice larvae were removed and counted to provide
direct evidence of ingestion. The larvae remaining free swimming in the container were
iv
preserved and counted. The proportion missing from the container was used to estimate
ingested larvae in statistical analyses. Two additional experiments investigating the effect
of bivalve size (small, medium, large) on the ingestion of sea lice larvae were conducted
with Pacific oysters and Pacific scallops. The heights for oysters (anterior-posterior axes)
were 19.2, 44.2, and 84.0 mm, and scallops (dorsal hinges to ventral margins) were 40.3,
64.1, 102.7 mm. The methodology for the size experiments was as previously described
for the temperature/diet experiments with the following changes: (1) the diet of larvae
alone was not used; (2) the mean number of larvae in each container was ~498; (3) the
mean concentration of TISO added to each container was ~7.8 x104 cells ml-1, and (4) the
mean water temperature was 10.4°C. The data for the four temperature/diet experiments
indicate that all four bivalve species ingested sea lice larvae, whether their diet included
phytoplankton or not, and that temperature had no significant effect. The data for the two
size experiments indicated that all three sizes of oysters and scallops ingested sea lice
larvae and that there was a significant size effect. Large shellfish consumed a
significantly greater proportion of the sea lice larvae than the small shellfish. Bivalves
grown at salmon net pens as part of an IMTA (Integrated Multi-Trophic Aquaculture)
system may be able to reduce the number of sea lice larvae as well as being an additional
crop of market value. Future research, conducted at a commercial scale at a salmon farm,
is warranted in order to determine if bivalves can serve in this role. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/3759 |
| Date | 21 December 2011 |
| Creators | Webb, Janis Louise |
| Contributors | Pearce, Christopher M., Cross, Stephen Fredrick |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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