Stress and Its Role in Fish Disease

When humans are stressed, bad things happen. People lose their tempers, indulge in unsafe or unwise behavior and become ill. When fish become stressed, they're unable to take a yoga class or pet a cat, and they can't throw a dish across the room or engage in primal screaming. The stress manifests by reducing the fish's immune system, leaving the fish less able to defend against disease.

  1. Stress Defined

    • Stress is a symptom of something out of your control. There's mental stress, such as when you can't solve that stupid math problem, and physical stress --you've committed yourself to volunteering in the hot sun all day and you're physically taxed. Stress happens when you can't improve your situation. For fish, improving their situation is not an option; they can't relieve stress like humans can, and so their bodies suffer the consequences.

    Stress = Bad

    • Stress is dangerous because it forces the body to endure a stimulus beyond the body's negligible limit. Just as stress can cause a host of physical and mental problems in humans, it can wreak havoc on fish. Some of the problems that cause stress in fish include bullies in a tank, dirty water, imbalance in chemicals, lack of food, sudden change in water temperature, infrequent water changes and, for some species, water conditions that aren't conducive to survival.

    Avoiding Stress

    • It's important to educate yourself on the compatibility of the fish in your community tank, as some fish species are notorious for being tank bullies. Know and understand the water temperature, alkalinity and acidity needs of all your fish; those with vastly differing requirements don't belong. Performing routine water changes means you'll remove less water each time and gets the fish accustomed to all the commotion created by changing the water. If you're changing the water infrequently, or when it looks dirty, the fish will freak out every time you do it. Lax attention to water changes will require you to remove 50 percent or more of the water to effectively clean the tank, risking upsetting the tank's chemical balance and temperature, and stressing out your fish.

    Stress and Disease

    • The alert aquarist will recognize the signs of stress in his fish. They may act differently: Formerly energetic fish may become lethargic, or fish who formerly swam languidly around the tank may dart about frantically. Some fish may lie on the bottom, some may drift near the top, others hide. In the early stages, there may be no symptoms at all. Tank-borne diseases stemming from bacterial, parasitic, viral or fungal infections can easily overcome a stressed-out fish's immune system, causing the fish to become seriously ill or die. Your fish are completely dependent upon your vigilance for their safety and well-being.