Euglena sanguinea, a species within the genus Euglena, displays a distinctive red coloration attributed to the presence of astaxanthin. In dense populations, these cells can tint water red. Astaxanthin serves to shield chloroplasts from excessive light; however, the cells can shift to a green hue as light levels fluctuate, relocating the red pigment to the cell center. Euglena sanguinea is notable for producing euglenophycin, a potent ichthyotoxin. Structurally similar to solensopsin found in fire ant venom, euglenophycin is unique to this species of euglenids. It is capable of forming toxic blooms that pose significant risks to fish farms, leading to measurable losses.