English abstract
The most complicated live organism relationship is between parasites and their hosts. Since this
interaction has increased attention because parasites have been shown to have a major impact on
population dynamics and the ecology of their hosts. The existing relationships between hosts and
parasites have developed through antagonistic interactions, leading to coevolutionary processes
that result in intricate reciprocal adaptations. Through these adaptations, parasites can take
advantage of the biological characteristics of their hosts, which helps to ensure their survival,
spread, and continued viability as a population.
Parasitism has been linked to variations in various aspects of fish behavior, including foraging
efficiency, habitat preference, shoaling behavior, predator-prey interactions, competitive prowess,
swimming ability, and sexual behavior, as well as mate selection. Fish also use techniques to
reduce the risk of contracting parasites, such as avoiding certain habitats, selectively targeting
prey, or steering clear of infected individuals. Additionally, they may engage in behaviors aimed
at removing parasites, such as scraping against substrates or seeking out cleaning stations.
Clinostomum sp. are digenetic trematodes characterized by genetic diversity and intricate life
cycles involving three hosts: snails, fish, and birds. The larval stages of these parasites have a deep
impact on the freshwater aquatic systems, particularly when infecting the second intermediate host,
fish.
Unfortunately, there have been no studies conducted on the morpho-molecular characterization of
Clinostomum sp. from freshwater fishes in the Sultanate of Oman. Furthermore, the prevalence of
Clinostomum sp. on freshwater fish remains unstudied, hindering efforts to comprehend its life
cycles, develop control strategies, and evaluate its impact on freshwater fish and aquatic
ecosystems in Oman.
Therefore, there is environmental and epidemiological research linked to Clinostomum parasites
needed in freshwater fish within Oman. In the present study, the Killifish Aphaniops sp. was
selected as the principal species due to its prominence in Omani freshwater ecosystems to evaluate
the prevalence and intensity of Clinostomum sp., characterize these parasites using a morphomolecular approach, and unveil their pathological effects on the host fish.
Live fish specimens were sampled from four distinct locations in the Muscat region: Al Amirat,
Al Khoud, and Darsait and Al Bahayes. All fish samples were measured length and weight to
compare parasite populations at the four different locations and fish sizes. In addition, the data of
parasites was categorized depending on infection locations and genders of host fish.
For identification of Clinostomum sp. morphologically characterized metacercaria as measuring
various organs of the parasite, identified them through DNA sequences from nuclear 28S-rRNA
(28S).
Randomly selected 5 fish from each sample site were divided into five sections to accommodate
sizing for cassette fixation and to focus on the most heavily infected body part and completed with
H&E staining to study the histopathological impact of the parasite on the host fish.
In the regions of Al Khoud, Darsat, and Al Amirat, 50 Killifish Aphaniops were gathered, with 39, 42, and
40 fish found to be infected, respectively. Conversely, in Al Bahayes, a total of 23 fish were collected, with
no parasitic infection observed across all samples. In other words, the prevalence of Clinostomum sp. was
highest in Darsat at 84%, followed by Al Amirat at 80%, Al Khoudh at 78%, and then Al Bahayes at 0%.
The parasites were infected more with females than males and the large size of the fish at all sampled
locations (P<0.05). More Clinostomum was found in the trunk region of the host fish than head and tail
regions. Morphological measurement of parasite result showed that Clinostomum on the host fish from
Omani freshwater body was clearly outranged (rather smaller) of existed two species of Clinostomum
species (Clinostomum complanatum and Clinostomum maginatum). More certainly, the DNA sequence
result showed Clinostomum from Oman was very close to Turkish Clinostomum complanatum but not the
same species. The histopathological impact of the fish tissue revealed the presence of Clinostomum within
the tissue layers. Lesions in the cavity tissues aligned with the destructive inflammatory response and cyst
encapsulation from infection. The present study confirmed Clinostomum sp. caused tissue inflammation
and the subsequent destruction and perforation of tissues of fish host.
The present study contributes valuable information to the understanding of the host-parasite interface within
freshwater ecosystem in freshwater ecosystems. The findings emphasize the importance of continuous
research and monitoring to develop comprehensive strategies for mitigating environmental hazards and to
conserve healthy aquatic ecosystems.
