Review of the effect of polyamines in microalgae when ingested by shellfish

Polyamines are a series of short-chain aliphatic amines which can be produced during the metabolism of cells, and are widely distributed in aquatic organisms. Polyamines are important regulators for physiological metabolism, which also eliminate active oxygen free radicals, maintain the normal physiological activities of living organisms, and improve plants' resistance to adverse stresses. However, the knowledge of functional characteristics of polyamines in algae, and their effects on the feeding habits of aquatic organisms, are still limited. In this review, the distribution and characteristics of polyamines in unicellular algae are evaluated. Different characteristics of polyamines in various types of algae, and the effects of polyamines being ingested by shellfish, are critically reviewed and analyzed. So far, most literature references offer the opinion that the partial functions of polyamines are similar to plant hormones. Some microalgae diets have different effects on bivalve mollusks, which could be partly due to characteristic changes of polyamines in algae cells, and their adaptability to external environmental pressure. The goal of this review is to discuss possible reasons why microalgae may be suitable for shellfish feeding. This may provide a new application for microalgae development, as a nutritional feed for shellfish.