Infection by Cardiodectes bellottii (Copepoda: Pennellidae) on Lampanyctodes hectoris (Actinopterygii: Myctophidae) in the southern Benguela Current upwelling ecosystem

Hector’s lanternfish Lampanyctodes hectoris is an abundant mesopelagic fish found in the Benguela Current marine ecosystem and is frequently parasitised by the copepod Cardiodectes bellottii. This parasite is relatively large compared with its fish host, and negative impacts of its infection on other lanternfishes have been reported. We examined 1 800 L. hectoris sampled over a wide spatio-temporal range in the southern Benguela to document C. bellottii infection indices in this lanternfish species, and we compare selected biological characteristics of infected and uninfected fish. Infection prevalence showed spatio-temporal variability, with an overall mean of 20.7% (95% confidence limits: 18.9–22.6%; 373/1 800 fish). This is the highest reported infection prevalence by C. bellottii among five lanternfish species for which large sample sizes (of >500 fish) were processed. We found that infection (i) significantly reduced female host weight-at-length but not that of male hosts; (ii) significantly reduced female but not male gonadosomatic index; and (iii) had no significant effect on length frequency distributions. Cardiodectes bellottii infection in L. hectoris does not appear to increase host mortality but can reduce both somatic and/or gonadal growth, and hence reproductive success. These findings suggest that the productivity and population dynamics of L. hectoris in the southern Benguela may be partly driven by infections by this parasitic copepod.