Host-parasite interactions between a copepod (Pharodes tortugensis) and small reef-associated gobies (Coryphopterus) in the British Virgin Islands

The effects of parasitic copepods on free-living hosts are infrequently
documented, and the copepod Pharodes tortugensis has remained virtually
unstudied since described.  For the first time, we document its
host range in the British Virgin Islands (BVI), the prevalence and
intensity of infections on wild hosts, and its impacts on host morphology
and performance.  Infections were observed on four benthic gobies
in the BVI (Coryphopterus glaucofraenum, C. venezuelae, C. dicrus and C.
eidolon) but not on other host species previously reported from other
parts of the western Atlantic.  Infected gobies were widespread
in the BVI (detected at 33 of 52 sites, prevalence from 1­–25%) but
extremely rare elsewhere in the Caribbean (detected at 2 of 16 sites,
prevalence <0.006%).  As is typical of macroparasite
infections, P. tortugensis was over-dispersed in BVI host populations
(mean intensity = 4.7, range = 1–17).  Infections were most
common in juvenile and female hosts, and rarely found in larger male
hosts.  The copepods attach in the branchial chamber of the goby;
female copepods show high attachment fidelity to the ventral surface of
the chamber, while male copepods attached most often to the first two gill
arches and in the branchial chamber adjacent to the female. 
Infections caused substantial damage to the host’s branchial chamber and
gill filaments.  Parasitized gobies also had larger livers and
smaller gonads than unparasitized individuals of similar length. The
changes in organ mass of infected gobies were not sizeable enough to
affect total body mass, and host condition (the body-length vs. body-mass
relationship) was similar for gobies with and without
infections.  Parasitized gobies were, however, significantly
smaller in body mass at a given age, reflecting slower overall growth.
Effects of P. tortugensis on individual hosts were broadly similar to
those of other parasitic copepods that infect fish gills and, for unknown
reasons, the BVI appears to be a persistent hotspot of infections on these
goby hosts.