Myxozoan infection in thinlip mullet Chelon ramada (Mugiliformes: Mugilidae) in the Sea of Galilee

Abstract

Mullets (Mugilidae) are economically important fish in Israel. Two species of mugilids (i.e., the thinlip mullet Chelon ramada and the flathead grey mullet Mugil cephalus) have been stocked in the Sea of Galilee (Lake Kinneret) in order to increase fishermen’s income and lake water quality. These catadromous species do not reproduce in the lake, consequently, fingerlings have been introduced every year since 1958. Following a survey of myxozoan infections in the Sea of Galilee, we described Myxobolus pupkoi n. sp. infecting the gill arches, and reported Myxobolus exiguus from visceral peritoneum and gall bladder of C. ramada. The prevalence of infection of both Myxobolus pupkoi n. sp. and M. exiguus were 11.5% (2/23). Our study indicates that the parasites infecting C. ramada belong to a lineage of myxozoans infecting mugilids. This result suggests that the infection took place in the Mediterranean Sea, where the fingerlings were caught, before their introduction into the Sea of Galilee. Since 2018 only farm-raised fingerlings have been introduced. We thus recommend to closely monitor the presence of these parasites in the future to determine if the presence of parasites disappear with the introduction of farm-raised fingerlings.

Myxozoan survey of thicklip grey mulletChelon labrosusreinforces successful radiation ofMyxobolusin mugiliform hosts

“…In the case of M. pupkoi , the small genetic difference determined between geographic isolates (0.7%) mostly took place at the 3′ end of the 18S rDNA sequence and, therefore, cannot confidently be taken as a premise of interspecific variability. Furthermore, our isolate shares the same site of infection and host genus with the Israeli isolate, with Gupta et al [ 21 ] even proposing that M. pupkoi was introduced into the Sea of Galilee via the Mediterranean Sea. Thus, the only considerable difference between our isolate and the Israeli isolate is myxospore morphometry, given that the myxospores observed in this study significantly surpassed the size range reported by Gupta et al [ 21 ].…”

“…A 99.3% similarity score matched the sequence of one Myxobolus isolate from the gills of C. labrosus with that of M. pupkoi ( OL605966 ) reported from the gill arches of C. ramada in the Galilee Sea off Israel [ 21 ], despite morphological comparisons showing significant differences between these geographical isolates (see Table 3 ). Although genetic similarity higher than 98% is usually considered to be representative of intraspecific variation among myxozoans [ 17 ], the boundary between myxobolid intraspecific and interspecific variability is not clear; there is no exact value of genetic similarity in the 18S rDNA sequences that determines whether two isolates can be discriminated as being conspecific or congener.…”

“…Overall, the comprehensive comparison of morphological, molecular, host-related, and geographic data performed in this study supported the description of these isolates as new species. The only exception was M. pupkoi , originally described from the gill arches of C. ramada in the Galilee Sea off Israel [ 21 ], and that was here identified from the gills of C. labrosus based on a 99.3% similarity score. This small genetic difference (0.7%) mostly took place at the 3′ end of the 18S rDNA sequence, with a few nucleotide differences occurring elsewhere (position 694: T vs. A; positions 1508–1509: C vs. Y; and position 1538: A vs. W).…”

“…Morphometric comparisons revealed significant differences among our isolates of M. pupkoi and the isolate reported by Gupta et al . [ 21 ] (see Table 3 ).…”

“…[ 40 ] reported hyperdiversification of Myxobolus spp. in mullet hosts, which presently account for more than 55 species of this myxozoan genus [ 8 , 21 , 37 , 39 , 40 , 45 , 52 ]. In Portugal, a total of 14 Myxobolus spp.…”