Effects of experimentally manipulated cortisol and nutrition on wound healing capacity in a teleost fish

Wound healing is a complex multi-system process that enables organs and tissues to re-establish their form and function post-injury. Exposure to stress and nutritional restrictions results in energetic trade-offs at a physiological level, usually at the expense of immunity and tissue repair. Relatively few studies have focused on how stress and nutrition mediate immune function and healing capacity in fishes. We subjected wild-caught pumpkinseed (Lepomis gibbosus (Linnaeus, 1758)) to a subcutaneous incision (a standardized wound) while experimentally manipulating plasma cortisol levels (via a slow-release cortisol implant) and nutrition (via restricting food intake) to evaluate how these affected wound healing over time (2, 7, and 14 d). Wound healing was poorest for cortisol-treated fed fish at 7 d post-implant. While cortisol implants resulted in lymphocyte apoptosis and neutropenia, which are well-described immunological responses to increased cortisol concentrations, fasting had little effect. Reproductively active males had different leukocyte counts than non-reproductive males, though the direction varied with leukocyte type, suggesting a trade-off in immune response during reproduction. The negative influence of cortisol on tissue repair and inflammation aligns with the wound healing literature across taxa. However, the ability of fasting to reduce these negative effects was unexpected and deserves further study.