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Volume :6 Issue : 24 1980      Add To Cart                                                                    Download

SEASONAL ABUNDANCE OF NEACHINORHYNCHUS AGILIS IN MUGIL HISHNI FROM SHATT AL-ARAB

Auther : By: A. Ismail Al-Hadilhri, Y. T. Daoud and A.H. Habash

 

A total of 525 Mugil fishes were collected from Shatt al-Arab River and its tributaries from December 1977 to November 1978. Investigation revealed that N. Agilis occurred in the intestine of 40% of the total number of fishes collected.

Records of incidence and intensity of infection showed that the parasite exhibits a seasonal cycle of incidence. Infection by N. Agilis occurs almost throughout the year. The initial infection by the new generation is quite apparent from the beginning of autumn. The Mugil fish may first acquire infection during the months of October, November and December when they crowd into the pools prior to spawning. Both incidence and intensity of infection were found to be highest in spring and declined during summer to their minimum values in July 1978.

Majority of the fishes caught were between 12-18 cm length. It was found that the length (age) of fish had significant effect on infection. The incidence of infection and the mean number of parasites in different length groups indicated that percentage of infection at first increased with increase in the length of the host and then declined in fishes above 15 cm. Long. The variation in the incidence and intensity of infection with length (age) of fish also suggests that the host develop resistance to infection.

It was found that 40% of 184 males and 44% of 291 females of the fishes were infected. The sex of the host had no relation with infection. This mean parasite burden of both males and females was greater in spring than in any other season. Female fishes carried more N. Agilis worms than male, although the difference was not statistically significant, and both sexes stand an equal change of infection by N. Agilis. Frequently distribution followed a negative binomial distribution. Temperature has an indirect affect on the incidence of infection, influencing the abundance of the intermediates host and the behaviour of the fishes as well as the growth of the parasite. It is postulated that the principal reason for the reasonable incidence and intensity of infection may be due to the change of food habits and behavior of the fish as its development proceeds:

Examination of stomach contents of fishes as well as cope ponds, which were collected from the same habitat during the period of study, revealed that cope ponds could not be considered definitely as intermediate host of the parasite.

The degree of pathological effect caused by N. agilis to the Mugil fishes depended largely upon the method of attachment. The worm was found to bury its proboscis deeply into the mucosal wall occupying more or less permanent position in the gut. The heavy feeding requirement of the worms lead to loss of weight of Mugil fishes.

The number of N. agilis per fish host was higher when solely infected by this parasite as compared to concurrent infection by both N. agilis and contracascum thus indicating a mutual antagonism and inhibition by these parasites.

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