Different populations of the whitespotted rabbitfish, Siganus
sutor, were examined for ectoparasites: adults from the
Mombasa area (sampled in December 1990) and different age classes (adult,
subadult and juveniles) from Gazi Bay
(sampled in December 1992 and August 1993). The most common gill parasites
were: the monogeneans Pseudohaliotrema
sp., Tetrancistrum sigani and Microcotyle mouwoi,
the copepods Hatschekia sp., Pseudolepeophtheirus
sp. and juvenile
Caligidae, and prazina larvae of the isopod Gnathia sp. Adult
siganids
had a higher parasite load than subadults. Juvenile
rabbitfish did not harbour any gill parasites. Temporal differences in
the
parasite load of subadult rabbitfish were observed
for M. mouwoi (highest in the December samples) and for juvenile
Caligidae (highest in August). The microhabitat of the
5 most common gill parasites was species specific. Most parasite species
showed distinct site preferences with respect to
both gill arches and gill sectors, within the gill arches. Niche
breadth of the different gill parasite species was independent
of the abundance of any of the other species present. However, niche
breadths of M. mouwoi, Tetrancistrum sp. and
Hatschekia sp. increased with their own abundance. This suggests
that interspecific competition for space is low and that
intraspecific factors could play an important role in the microhabitat
choice of these gill parasites. The hypothesis that
niche restriction leads to higher intraspecific contact and an
enhancement of chances to mate was tested on 2 monogenean
species, Pseudohaliotrema sp. and Tetrancistrum sigani.
Their highly aggregated distribution over the gill filaments, leading
to increased intraspecific contact, is consistent with the hypothesis.