Short-term dietary supplementation with the microalga Parietochloris incisa enhances stress resistance in guppies Poecilia reticulata

Two trials were conducted to determine the e¡ects of dietary enrichmentswith themicroalgaParietochloris incisa, rich in arachidonic acid (ARA), on stress resistance in guppies Poecilia reticulata.The microalgawas added to commercial diets as a neutral lipid (NL) extract and its fractions or as broken cells. Experimental diets were applied for a period of 14 days. In trial 1, commercial diets were supplemented with NL (containing 25mg ARA and 0.11mg b-carotene g 1 feed), its triacylglycerol (TAG) fraction (containing 25mgARAg 1 feed and no b-carotene) and the b-carotene fraction (containing 0.11mgcarotenoidg 1 feed andminute amounts of ARA). Neutral lipid-fed ¢sh demonstrated the highest resistance (Po0.05) to osmotic stress (32-ppt NaCl), followed by ¢sh fed with diets supplemented with TAG and b-carotene alone, which were more resistant than control (Po0.05). In trial 2, ¢sh fed diets supplementedwith higher levels of broken alga (26.1mgARAg 1 feed) were more resistant (Po0.05) to stress as compared with ¢sh fed lower ARA (16.3mggg ) or an unsupplemented control diet.We suggest a dietary supplementationwith broken P. incisa cells to enhance stress resistance in guppies before a stressful event.