Isopoda infestation and its effects on the reproductive maturation of Nemipterus japonicus in Red Sea

Isopoda infestation and its effects on the reproductive maturation of
Nemipterus japonicus in Red Sea
Magdy M. El-Halfawy1
; Heba I. Abdel-Mawla2
and Amal M. Ramadan1
1 National Institute of Oceanography and Fisheries,
Fish reproduction & induced spawning Lab.
Suez and Aqaba Gulfs Branch, P.O;182, Suez
* Corresponding author : E-Mail [email protected] 2
Dep. of Fish Diseases, Animal Health Research Institute (Ismailia Branch).
Received 5th November 2011, Accepted 15th December 2011
Abstract
This study had been carried out at the National Institute of Oceanography and Fisheries in cooperation with
Animal Health Research Institute. A total of 250 marine fish (Nemipterus japonicus) of different body weights were
randomly collected in different seasons from the Red Sea at Suez Gulf. The Isopoda was found unilaterally in most
cases in the opercular cavity as a single parasite per fish. It was identified as Cymothoid isopoda (Irona nanodies).
The total prevalence of infestation was 41.6%, the highest recorded infestation was in summer (53.3%) followed by
spring, autumn and winter, where the prevalence rates were 39.7%, 37.5% and 31.1% respectively. The
prevalence of infestation was slightly higher in females than in males (43% and 40.4% respectively). Clinical signs,
postmortem lesions and parasitological findings as well as the isopod-fish relationship were discussed. The potential
effect of isopods on the reproductive investment of the host was measured by gonad maturation and gonado-somatic
index (GSI). Isopoda infestation was studied during periods of spawning where the fishes were more susceptible to
infection. Parasitized females had fewer, smaller and less mature ova compared to un-parasitized females, and lower
gonado-somatic index (GSI) for male and female.
Keywords: Isopods, Nemipterus japonicus, Irona nanodies, Reproduction.