Gyrodactylids (Gyrodactylidae, Monogenea) infecting Oreochromis niloticus niloticus (L.) and O. mossambicus (Peters) (Cichlidae): A pan-global survey

Abstract

Gyrodactylus infections in intensively-reared populations of Nile tilapia, Oreochromis niloticus niloticus, have been associated world-wide with high mortalities of juvenile fish. In this study, 26 populations of Gyrodactylus parasitising either O. n. niloticus or Mozambique tilapia, Oreochromis mossambicus, were sampled from fourteen countries and compared with type material of Gyrodactylus cichlidarum Paperna, 1968, Gyrodactylus niloticus (syn. of G. cichlidarum) and Gyrodactylus shariffi Cone, Arthur et Bondad-Reantaso, 1995. Representative specimens from each population were bisected, each half being used for morphological and molecular analyses. Principal component analyses (PCA) identified five distinct clusters: (1) a cluster representing G. cichlidarum collected from O. n. niloticus from 13 countries; (2) the G. shariffi paratype; (3) three specimens with pronounced ventral bar processes collected from two populations of Mexican O. n. niloticus (Gyrodactylus sp. 1); (4) four specimens collected from an Ethiopian population nominally identified as O. n. niloticus (Gyrodactylus sp. 2); (5) nine gyrodactylids from South African O. mossambicus (Gyrodactylus sp. 3). Molecular analyses comparing the sequence of the ribosomal transcribed spacer regions (ITS 1 and 2) and the 5.8S gene from the non-hook bearing half of worms representative for each population and for each cluster of parasites, confirmed the presence of G. cichlidarum in most samples analysed. Molecular data also confirmed that the DNA sequence of Gyrodactylus sp. 2 and Gyrodactylus sp. 3 (the morphologically-cryptic group of South African specimens from O. mossambicus) differed from that of G. cichlidarum and therefore represent new species; no sequences were obtained from Gyrodactylus sp. 1. The current study demonstrates that G. cichlidarum is the dominant species infecting O. n. niloticus, being found in 13 of the 15 countries sampled.

Description of three new species of Gyrodactylus von Nordmann, 1832 (Monogenea) parasitising Oreochromis niloticus niloticus (L.) and O. mossambicus (Peters) (Cichlidae)

“…nov. are morphologically similar to those of G. cichlidarum, a PCA analysis of the morphometric data suggested that they can be separated (see García-Vásquez et al 2010). This finding was supported by a parallel molecular analysis which identified 42 nucleotide differences in the ITS regions between the two species.…”

“…nov. and G. cichlidarum are subtle and although a principal components analysis (PCA) of morphometric data suggested a difference (see García-Vásquez et al 2010), their clear differentiation from each other was confirmed by the molecular study. Altogether, there are 42 differences between the ITS1 and ITS2 of G. ulinganisus sp.…”

“…The form of G. cichlidarum redescribed and characterised by García-Vásquez et al (2007) has a wide distribution range extending from the Philippines to Mexico and across the entire length of the African Continent (Israel, Egypt to South Africa) (see García-Vásquez et al 2010). The holotype of G. cichlidarum, however, was described from a Ghanaian population of S. g. galilaeus.…”

“…1 in García-Vásquez et al 2010 Host: Oreochromis niloticus niloticus (L.) (Cichlidae), cultured stock.…”

“…The current paper formally describes the three discrete forms identified by morphometric and molecular methods in García-Vásquez et al (2010) …”