of larval stage data. Kruskal–Wallis and Mann–Whitney U-tests were used to compare the mean number of lice within and amongst the three salmonid species as well as the
differences in the developmental stages of C. flexispina between species.
3. Results
Ž .
C. flexispina was found to be significantly more prevalent and abundant p - 0.001 Ž
. on rainbow trout in farmed pens, than on atlantic and coho salmon Table 2, Fig. 2
which show no differences when raised at the same site. The majority of copepods present on rainbow trout were adults, whereas most copepods on coho and atlantic
Ž .
Ž .
Fig. 4. Percentage of chalimus ch , pre-adults and adults pa-a of C. flexispina in netpens in the south of Ž .
Ž . Chile A and 9 days post-infection in the fourth experiment in tanks B .
Ž .
salmon were earlier developmental stages Fig. 4A . No ovigerous females were found on coho salmon. Prevalence and density of C. flexispina on rainbow trout was higher
than on either atlantic or coho salmon during all cohabitation trials and sampling dates, Ž
. p - 0.01 . With the exception of trial 4, atlantic salmon appears to be the next most
Ž .
susceptible to infection and coho salmon the most resistant Table 3, Fig. 3 . At the end of trial 1 most of the copepods present on rainbow trout were chalimus IV and
pre-adults. The one copepod found on coho salmon was an ovigerous female. A coho salmon sampled at 6 days post-infection was infected with six chalimus larvae.
In trial 4, at the 2nd day post-infection, 40.5 copepodids and chalimus I collected in Ž
. all the samples were attached to rainbow trout mean abundance s 9.9 2.7 , 42.2
Ž .
were on coho salmon mean abundance s 4.4 1.1 and only 17.2 were on atlantic Ž
. salmon mean abundance s 11.1 2.2 . At the time, atlantic salmon showed a signifi-
Ž .
cantly lower number of copepodids than the other two salmonid species p - 0.001 . At 9 days post-infection, the highest density of copepods collected was on rainbow trout
Ž .
followed by coho salmon and then atlantic salmon Table 3, Fig. 3 . Nine days
post-infection a high proportion of the copepods had reached the pre-adult and adult stages with significantly more copepods attaining these stages on rainbow trout than on
Ž .
either atlantic or coho salmon p - 0.001 . At the time, 26 of copepods collected from Ž
. rainbow trout were pre-adults or adults Fig. 4B . On atlantic and coho salmon 10 and
6, respectively were pre-adults or adults. No adults were collected from coho salmon.
4. Discussion
