Two types of coccidian parasites: Eimeria and Isospora were described from three species of fishes found in Saudi Arabia. Eimeria sp.1 infecting Argyrops sp.; Eimeria sp.2 & Eimeria sp.3 infecting Rastrelliger sp. and Eimeria sp.4 & Eimeria sp.5 and Isospora sp. infecting Oreochromis niloticus (from a fish farm). Oocysts of Eimeria sp.1 were spherical to subspherical, measured 29.5- 35.7μm in length and 25.5-28.8μm in width (mean: 31.7 x 29.4 μm) and L/w
ratio was 1.08. Oval to ellipsoid sporocysts measured 13.4-15.6μm in length and 9.3-11.8μm in width (mean: 13.3 x 10.6μm) and with a stieda body. Sporozoites measured 10.0-11 .3μm in length and 4.0-5.3μm in width (mean: 11.3 x 4.8 μm). Oocysts of E. sp.2 were spherical and characterized by their large size, being 38.1-41.6μm in diameter (mean: 40.3 μm). The outer layer of oocyst wall was thicker than the inner one. Sporocyst lacking stieda body and measured
14.0-16.6μm in length and 12.1-13.5 in width (mean: 15.8 x 13.5 μm). Sporozoites were elongated and tapering at both ends. They measured 8.1-9.4 in length and 4.6-5.8μm in width (mean: 9.1 x 5.4 μm). Oocysts of E.sp.3 were
small in size, measuring l7.5-20.9μm in diameter (mean: 19.6μm). Sporocyst had small stieda body and measured 7.4-9.5μm in length and 5.3-6.0μtm in width (mean: 8.6 x 5.7 μm). It contains a scattered residuum. 3.0 Sporozoites
were banana shaped and measured 6.0-7.5μm in length and 3.O-4.1μm in width (mean: 7.0 x 3.6 μm).
Esp.4 oocysts were subspherical and measured 35.1 -37.5μm in length and 29.6- 34.0 μm in width (mean: 36.8 x 32.5 μm) and L/w ratio was 1.13. The ovoid sporocyst had a nipple-shaped stieda body and measured 5-16.0μm in length and
8.9-11.8 μm in width (mean: 14.1 x 1 0.5μm). Sporozoites were arranged head to tail in each sporocyst and measured 10.8-12.9 μm in length and 5.5-6.8μm in width (mean: 12.0 x 6.1 μm). Oocysts of Esp.5 were larger in size than those of
Esp.4 oocysts. They measured 48-5l.5μm in length and 8-49.5μm in width (mean: 50.7 x 48.4 μm) and L/w ratio was 1.05. They had one polar granule. Oocysts of Isospora sp. were ovoidal in shape and measured 27.6- 30.7μm in length and 25.5-27.2 μm in width (mean: 29.5 x 26.2 μm) and L/w ratio was 1.13. The sporocysts lacked a stieda body and measured 16.0-19.2 μm in length and 9.3-11.8μm in width (mean: 18.0x 12.8 μm.