- Two trials were conducted to determine the effect of dietary enrichment with arachidonic acid (ARA)-rich triacylglycerols fraction, obtained from the microalga Parietochloris incisa, on the recovery of guppies, Poecilia reticulata, from infection with Tetrahymena sp. Commercial feed (0.7 mg ARA g− 1 feed) was directly enriched with the algal hexane lipid extract. Three (12.5, 25.0, 50.0 mg ARA g− 1 feed) and four (12.5, 25.0, 37.5, 50.0 mg ARA g− 1 feed) experimental diets were utilized in the first and second trials, respectively. Guppies were fed with ARA-supplemented feed for 14 days followed by infection with 1000 Tetrahymena sp. cells mL− 1. Supplemented diets significantly altered the fatty acid composition in fish body (whole body with the exception of the digestive tract and liver) and liver. The share of ARA in fatty acids of bodies and livers increased commensurately with the amount of ARA in feed. Livers accumulated the highest levels of ARA, resulting in drastic changes in the docosahexaenoic acid (DHA)/ARA and eicosapentaenoic acid (EPA)/ARA ratios.Feeding with an algal extract that produced an ARA concentration in feed of 25 mg g− 1 significantly enhanced the ability of fish to recover from the disease in both experiments, as compared to the control and feed supplemented with 12.5 mg g− 1of ARA. Although not significantly different, further increase in fed ARA (50 mg g− 1 feed) reduced the recovery as compared to the 25 mg g− 1 treatment.