Abstract
A new species of Gyrodactylus von Nordmann, 1832 is described from the gills of Alcolapia grahami, a tilapian fish endemic to Lake Magadi. This alkaline soda lake in the Rift Valley in Kenya is an extreme environment with pH as high as 11, temperatures up to 42 °C, and diurnal fluctuation between hyperoxia and virtual anoxia. Nevertheless, gyrodactylid monogeneans able to survive these hostile conditions were detected from the gills the Magadi tilapia. The worms were studied using light microscopy, isolated sclerites observed using scanning electron microscopy, and molecular techniques used to genetically characterize the specimens. The gyrodactylid was described as Gyrodactylus magadiensis n. sp. and could be distinguished from other Gyrodactylus species infecting African cichlid fish based on the comparatively long and narrow hamuli, a ventral bar with small rounded anterolateral processes and a tongue-shaped posterior membrane, and marginal hooks with slender sickles which are angled forward, a trapezoid to square toe, rounded heel, a long bridge prior to reaching marginal sickle shaft, and a long lateral edge of the toe. The species is also distinct from all other Gyrodactylus taxa based on the ITS region of rDNA (ITS1–5.8s–ITS2), strongly supporting the designation of a new species. These findings represent the second record of Gyrodactylus from Kenya, with the description of G. magadiensis bringing the total number of Gyrodactylus species described from African cichlids to 18.
Highlights
Formalin fixed worms were washed in water, dehydrated in a series of ethanol (30%, 50%, and 70% ethanol), and subsequently mounted and cleared in glycerine ammonium picrate (GAP) [40] for examination of the haptoral sclerites and male copulatory organ (MCO)
Gyrodactylus magadiensis n. sp. is the second record of a Gyrodactylus species infecting a cichlid from Kenya
This is the first gyrodactylid to be described from the extreme conditions of Lake Magadi and from Alcolapia grahami
Summary
The Magadi tilapia has developed exceptional morphological and physiological adaptations, especially to cope with the high pH, extreme alkalinity, and the shifting oxygen availability. These include: (a) excretion of nitrogenous waste in the form of urea instead of ammonia through the ornithineurea cycle [69], (b) an atypically thin blood–water barrier in the gills [38, 40], and (c) the use of the swim bladder as a primitive air-breathing organ [40]
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