Immunostimulation in the rainbow trout (Oncorhynchus mykiss) following intraperitoneal administration of Ergosan

The present work provides information concerning the immunostimulatory activity of Ergosan, an algal based product, injected intraperitoneally in the rainbow trout (Oncorhynchus mykiss). Ergosan is composed of 0.002% unspecified plant extract, 1% alginic acid from Laminaria digitata, and 98.998% algal based carrier. Migration of leucocytes into the peritoneal cavity was stimulated at doses ≥1 mg ml−1. A single dose of 1 mg significantly augmented the proportion of neutrophils, degree of phagocytosis, respiratory burst activity and expression of interleukin-1β (IL-1β), interleukin-8 (IL-8) and one of the two known isoforms of trout tumour necrosis factor-α (TNF2) in peritoneal leucocytes at 1 day post-injection. Humoral immune parameters were less responsive to intraperitoneal Ergosan administration, with complement stimulation only evident in the 1 mg treated group at 2 days post-injection. Antiprotease and lysozyme activity were unaffected by Ergosan over a 7-day time period at the doses examined.