Parasites of Moroccan desert Coptodon guineensis (Pisces, Cichlidae): transition and resilience in a simplified hypersaline ecosystem

Abstract

Sebkha Imlili (Atlantic Sahara) is a salt flat with over 160 permanent holes of hypersaline water generated in the Holocene and inhabited by euryhaline organisms that are considered to be relics of the past, including the cichlid fish Coptodon guineensis. We surveyed the fish parasites four times over one year, to i) identify the parasites, and ii) determine possible seasonality in infection patterns. Over 60% of the fish were infected by one to three helminths: an acanthocephalan in the intestine and two digenean metacercariae in the kidney, spleen, liver, muscle, and mesenteries. The acanthocephalan Acanthogyrus (Acanthosentis) cf. tilapiae was identified morphologically and molecularly; only one digenean (the heterophyid Pygidiopsis genata) could be identified molecularly. Both identified parasites were present throughout the sampling periods; the unidentified metacercariae were present only in summer and fall. Mean intensities, but not prevalence of infection by the acanthocephalan, reflected a biannual pattern of transmission. Infection accrued with fish size, possibly due to cannibalism. Because the water holes include only a few invertebrates, the intermediate hosts of these parasites can be inferred to be the gastropod Ecrobia ventrosa for the digeneans and either the copepod Cletocamtpus retrogressus or the ostracod Cyprideis torosa for the acanthocephalan. This ecosystem appears stable and provides a window into the past, as the acanthocephalan likely switched from freshwater tilapia to C. guineensis when the Sebkha formed. However, this is a vulnerable environment where the survival of these parasites depends on interactions maintained among only very few hosts.

Species depauperate communities and low abundances of monogenean gill parasites at the edge of the natural distribution range of their cichlid hosts in northern Africa

“…Generally, the overall ecological conditions become increasingly difficult and stressful as one moves to the edge of the native range of a species (Gaston, 2003). In Morocco, the studied host species and their parasites are therefore at the limit of their distribution area; they are subject to bottleneck events and are isolated in small gueltas, where abiotic conditions are suboptimal (hydrological stress: strong variations in temperature, salinity and oxygen content) (Louizi et al, 2019). The low parasite diversity and load reported herein thus supports the enemy release hypothesis (Drake, 2003).…”

“…The absence of these same two species (C. zillii and O. aureus) in the Al Wa'er, Oumma Fatma and Chbika wadies complex could have an opposite explanation: either they never reached this wadies complex over the course of time in view of its isolation, or they disappeared following episodes of drought. On the other hand, C. guineensis, the only one present in this watershed, was able, after having arrived from the sea, to move upstream in these wadies in the absence of competition with C. zillii and therefore colonize these rivers upstream of their mouth (Louizi et al, 2019). Recently, two specimens of C. guineensis were unexpectedly found in the Canal de Nador (Ainou et al, 2021), nearly 1000 km north of the Wadi Aabar, the northernmost locality where this species was previously recorded (Qninba et al, 2012).…”

“…Consequently, their diversity in these watersheds is then logically low (Louizi et al, 2019); (Ainou et al,2021).…”

“…Cichlids are widely distributed in Africa, Central and South America, the Middle East and parts of South Asia, while fossils have been found in Europe (Italy) (Nelson, 1994). In Morocco, cichlids are tropical relics from the last glacial episodes (Lévêque, 1990); they are represented by small isolated populations (Louizi et al, 2019). They are naturally represented by only two genera: Coptodon Gervais, 1848 and Oreochromis Günther, 1889, with three native species: Coptodon zillii (Gervais, 1848), C. guineensis (Günther, 1862), and Oreochromis aureus (Steindachner, 1864).…”

“…They are naturally represented by only two genera: Coptodon Gervais, 1848 and Oreochromis Günther, 1889, with three native species: Coptodon zillii (Gervais, 1848), C. guineensis (Günther, 1862), and Oreochromis aureus (Steindachner, 1864). A fourth species, O. niloticus (L, 1758), has been introduced into northern Morocco for aquaculture purposes (Louizi et al, 2019;Ainou et al, 2021).…”