Effects of Laminarin on Innate Immune Activation in White Shrimp (Litopenaeus vannamei) Reared at Different Salinities

Abstract

This study examined the effects of laminarin on the haemocytes of white shrimp (Litopenaeus vannamei) reared at different salinity levels (35 ‰, 25 ‰, 15 ‰, and 10 ‰) in vitro. Haemocytes incubated with 1 mg/mL laminarin were assessed for degranulation, cell size, viability, necrosis, phenoloxidase (PO) activity, and respiratory burst (RB). Shrimp haemocytes incubated with laminarin for 30 minutes exhibited greater degranulation and necrosis at salinities of 35‰, 25‰, and 15‰ than those of shrimp reared at 10‰. The reduction increased with increasing laminarin concentration incubated with white shrimp haemocytes, but was negatively related to salinity level. The phenoloxidase (PO) activity and respiratory burst (RB) of shrimp increased with increasing salinity. It is concluded that haemocytes of white shrimp reared at 10‰ and treated with laminarin showed lower immune activation, as indicated by reduced degranulation, lower necrotic cell levels, a lower percentage of large cells, and a lower percentage of viable cells, as well as decreased PO activity and RB. In contrast, the immune response of white shrimp treated with laminarin was stronger and occurred earlier in shrimp reared at higher salinities (35‰, 25‰, and 15‰) compared with those reared at low salinity (10‰).