Prevalence of parasitic infections
Fish are considered one of the important sources of animal protein (
de Boer et al., 2020)
. Sea breams are fish of considerable economic importance and are commonly affected by several pathological problems, which can lead to mortalities and loss of production
(Bannai, 2018). The examined solider bream fish,
A.
filamentosus, was found to be naturally infected with three Monogeneans, ectoparasitic flatworms. Identification of parasitic taxa of sea breams associated with their morphological and biological peculiarities. Molecular techniques provide useful alternatives to morphology for the identification of parasites
(Chaudhary et al., 2015; Abdel-Gaber et al., 2023). Monogeneans isolated from the gills of the solider bream fish were identified as
Protolamellodiscus senilobatus Kritsky, Jiménez-Ruiz and Sey, 2000 (F: Diplectanidae),
Acleotrema maculatus Morsy,
El-Fayoumi and Fahmy (2014) (F: Diplectanidae) and
Haliotrema susanae Soo, 2019 (F: Ancyrocephalidae) with a prevalence rate of 70 (21/30) for
P.
senilobatus, 46.66% (14/30) for
A.
maculatus and 50.00% (15/30) for
H.
susanae. Mixed infection for the recovered parasites was recorded to be 33.33% (10/30). Little information is available on parasitic infections of the soldier bream fish and the specificity with its host. Therefore, the present study provided more data on parasite fauna in this sparid fish species and confirm its taxonomic position.
Molecular barcoding of Argyrops filamentosus fish
DNA barcoding is considered to be an efficient tool to identify fish species within an ecosystem and to evaluate the genetic variability within species
(Rajkumar et al., 2015; Panprommin et al., 2019; Ghouri et al., 2020; Alshehri et al., 2022). In the present study, the partial sequences of the mt COI gene were amplified by PCR that generated 539 bp fragment. The average base-pair proportions for the COI gene were A(24.49% 132) | C(28.01% 151) | G(16.14% 87) | T(31.35% 169), which is consistent with
Ward et al., (2005), Ivanova et al., (2007), Armani et al., (2012), Consuegra et al., (2015) and
Cutarelli et al., (2018). PCR products were deposited in GenBank under the accession number OP975758.1. The ML approach was used to align nucleotide sequence data from 24 taxa over 530 positions to produce a phylogenetic dendrogram that represented different marine species (Table 1).
There is a low intra-species variation (0.076) for COI among all specimen sequences, agreeing with
Xia et al., (2008), Renxie et al., (2018) and
Ceruso et al., (2020) who also observed the lower intraspecific distance between comparable sparid fish. The results validate that COI is a useful marker for species diagnosis in the family Sparidae. One family (Sparidae) for the fish host (
Argyrops filamentosus) was identified for the recovered monogenean parasites. The phylogenetic relationship of the family Sparidae is supported by previous data from
Day (2002) and
Chiba et al., (2009). All the GenBank entries that matched our COI sequence under the highly stringent criteria (89.90-99.44% identity, 98-100% query coverage and E-value 0.0) were assigned to two monophyletic groups within family Sparidae for
A.
spinifer and
A.
filamentosus. In ML analyses (Fig 1), the taxa of
Argyrops were grouped in a distinct clade with high bootstrap values. Dendrograms confirmed the association of our specimen with the
Argyrops group, with special reference to
Argyrops filamentosus (JF492876.1, KJ012288.1, KJ012287.1, HQ945946.1 and HQ945852.1) that found in South Africa and the Indian Ocean. This study confirms the high efficacy of DNA barcodes for the identification of sparid fish.
Histopathological studies
The histopathological alterations of the infected gills were observed and compared to the control sections of
A.
filamentosus (Fig 2).
The damages are consistent with
Purivirojkul (2012) reported that infection with monogeneans is one of the most prevalent parasitic agents affecting gills and destroying gills which leads to impairment of fish respiration as well as a general deterioration of fish health. Microscopic examinations revealed that the gills from control fish consisted of horizontal flat filaments and were supported by bony gill arches. On these filaments, secondary lamellae were found. These lamellae are composed of a thin epithelial cell layer covering pillar cells, which in turn surround the blood sinusoids. Monogenean parasites were attached to the secondary gill lamella of infected fish. Parasites penetrated deeply with their haptor to the gill lamella and caused damage and degeneration of epithelial cells leading to the formation of a cup-shaped depression. Nevertheless, the major host response to monogenean infection was represented by hyperplasia of the gill filament. The severity of respiratory damage for the fish host was directly proportional to the number of parasites on the gills. This agreed with
Campos et al., (2011) and
Pahor et al., (2017) stated that when the intensity of monogenean parasites increases, the gill damage may be serious with the pronounced impact of the histology and lead to fish mortality. Because of these damages, hyperplasia of gill epithelium associated with monogenean anchors was observed, which agreed with
Shamsi et al., (2009), Raissy et al., (2011), Pahor et al., (2017) and
Hoai (2020) also noticed hyperplasia of the epithelial cells, subsequent lamellar fusion and extensive secretion of mucus. Moreover, these results agreed with those observed on the gill filament of
Plectropomus maculatus infecting
Acleotrema maculatus (
Morsy et al., 2014),
Pagellus erythrinus infecting
Diplectanum aequans (Adawy et al., 2016),
Gyrodactylus cichlidarum infecting
Oreochromis niloticus (Grano-Maldonado et al., 2018),
Cichlidogyrus philander infecting
Pseudocrenilabrus philander (Igeh and Avenant-Oldewage, 2020),
Dactylogyrus spp. infecting
Epinephelus coioides (
Ramudu et al., 2020); and three species of monogeneans
Anacanthorus spathulatus,
Notozothecium janauachensis and
Mymarothecium boegeri infecting
Colossoma macropomum (Tavares-Dias et al., 2021).
