Diplostomum spp.

Sarabeev, V., 2015, Mortality Of Juvenile So-Iuy Mullet, Liza Haematocheilus (Teleostei, Mugilidae), In The Sea Of Azov Associated With Metacercaria (Digenea), Vestnik Zoologii 49 (6), pp. 537-550 : 543-545

Diplostomum spp.

Metacercariae were found in eye lens of host species. Fry and juveniles of L. haematocheilus from the Molochny Estuary were infected by Diplostomum spp. in 1997 and 1999, but in the subsequent years this metacercaria was not found in the fish samples (table 1). Metacercariae of Diplostomum spp. were recorded in so-iuy mullet beginning from the first month of its life. Two of 37 dissected fish in age about 1 month were infected by a single specimen of Diplostomum per capita. Metacercariae were not found in two month old juvenile fish. Beginning from the age of three months the parasite mean abundance steadily increased up to two years old while the prevalence reached the maximum value of 51 % in adult fish. The regression analysis performed on linear measurements of fish and the number of helminth specimens per host further supports the observed infection pattern, revealing positive relationships between fish length and parasite intensity ( fig. 3 ).

The relationships between the VMR, the exponent k and the prevalence are approximately linear in Diplostomum spp. (R 2 = 0.87, p <0.001; R 2 = 0.89, p <0.01, respectively), moreover the VMR also moderately correlated to the mean abundance (R 2 = 0.66, p <0.05). The distribution patterns of Diplostomum spp. in the most samples did not fit well to the NBD in all age groups except the age of two years old (table 1). The estimated over-dispersion pattern measured by the VMR in fry and juveniles was relatively low in range 1–26.6. The VMR reached a maximum value in the fish of two years old, corresponding to the maximum mean abundance. A steady increase in k (decrease in aggregation) with age was observed,

intensity transformed

Log

Log transformed fish total length the lowest value was reported for three month old fish and the highest for the adult group.

Juvenile fish from three months to two years old were selected to execute the frequency analysis. The best fit of the observed data to the estimated frequency was found for the negative binomial parameters obtained from the fish with 0–5 parasites. The observed frequency with 1–4 parasites was less than expected (table 2), but we made the assumption that fish with 5 parasites do not die as the result of their infection. The observed frequencies with 5 and more parasites were very close to or higher than expected. Thus, the truncation model indicated that the parasite-related mortality had not occurred among fish infected by Diplostomum spp.

Figures

Fig. 3.Relationship between the fish total length and the intensity of Diplostomum spp. in juveniles of L. haematocheilus.* Referred to a significant level of 95 %.