Growth hormone increases aggressive behavior in juvenile rainbow trout

Area of Science:

• Animal Behavior
• Endocrinology
• Fish Biology

Background:

• Growth hormone (GH) is known to increase metabolic demands and feeding motivation in fish.
• GH's impact on social interactions, specifically aggression and fighting ability, requires further investigation.

Purpose of the Study:

• To determine the role of growth hormone in modulating social interactions in juvenile salmonids.
• To test the hypotheses that GH increases aggression and/or fighting ability.

Main Methods:

• Observing agonistic behavior in pairs of juvenile rainbow trout (Oncorhynchus mykiss).
• Experimental groups included control/control (C/C), growth hormone-treated/growth hormone-treated (GH/GH), and control/growth hormone-treated (C/GH) pairs.
• Recording the initiator and winner of each aggressive act.

Main Results:

• Aggression levels were significantly higher in GH/GH pairs compared to C/C pairs.
• Aggression was intermediate in C/GH pairs, indicating GH increases aggression.
• No significant difference in conflicts won by GH-treated versus control fish in C/GH pairs, suggesting GH does not enhance fighting ability.

Conclusions:

• Growth hormone significantly increases aggression in juvenile rainbow trout.
• GH does not appear to improve fighting ability or social status.
• GH may indirectly increase aggression by enhancing swimming activity or territory defense, leading to more encounters.