During a survey on fishes of the Tasik Kenyir Reservoir, Malaysia, 5 new Myxobolus spp. and 2 known Henneguya spp. were found. The specific locations for 2 Myxobolus spp. were the host's muscles, while 2 other Myxobolus spp. were found to develop in the host's kidney and gills, respectively. Of the species developing intracellularly in muscle cells, M. terengganuensis sp. nov. was described from Osteochilus hasselti and M. tasikkenyirensis sp. nov. from Osteochilus vittatus. M. csabai sp. nov. and M. osteochili sp. nov. were isolated from the kidney of Osteochilus hasselti, while M. dykovae sp. nov. was found in the gill lamellae of Barbonymus schwanenfeldii. Henneguya shaharini and Henneguya hemibagri plasmodia were found on the gills of Oxyeleotris marmoratus and Hemibagrus nemurus, respectively. Description of the new and known species was based on morphological characterization of spores, histological findings on locations of plasmodia and DNA sequence data.
Tor tambroides, a common and appreciated cyprinid fish of the Tasik Kenyir water reservoir in Malaysia, is one of the species selected for propagation. This fish was first successfully propagated in Malaysia by the Department of Agriculture, Sarawak, Malaysia, and the breeding program continued throughout the country. The gills were frequently infected by a Myxobolus species to be described as Myxobolus tambroides sp. n. The small, 50 to 70 μm, round plasmodia of this species is located intralamellarly. Plasmodia were filled with pyriform myxospores, 9.9 and 7.4 μm wide. In sutural view, the caudal end of the myxospores had a distinctive valvular groove, parallel with the suture. Plasmodia caused deformations on the affected and the neighbouring gill lamellae. The 18S rDNA sequence of M. tambroides sp.n. did not show a close relationship with any other Myxobolus spp., represented in the GenBank. This might be an emerging parasite likely to impact the propagation of this fish.