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74 • Nebraska Game and Parks Commission Many times it is seen on the tail, sides, or belly of fish which have rubbed these areas while spawning or on fish that have been mishandled. Some affected fish will die, but most will recover. A protozoan (Ichthyophthirius spp.), often called "ich," can be very harmful to fish. Many aquarium owners are familiar with this fish- killing parasite. The elimination of ich from a pond is virtually impossible, so prevention is important. By maintaining good water quality in the pond and only stocking healthy fish, ich should not be a problem. Virus and bacteria are microscopic organisms that cannot be seen with the naked eye. However, an angler can see their symptoms, which range from "pop-eye" to swollen, bloody fins. Their diseases are common in all fish and occur most often when environmental conditions, such as water quality, are poor. Inadequate oxygen levels in the pond can stress fish and make them susceptible to infections. These infections are often associated with spring die-offs in ponds. As the water warms in the spring, fish weakened by the stress of winter can be affected by bacteria/ virus and die. Spring spawning activity adds another stress to weakened fish that can increase the number of deaths. The loss of fish to these infections is fairly common in May and June. When a die-off does occur, it is often dominated by one species. If there is a high density of one species, particularly crappies, a disease outbreak can result in a substantial die-off. There is no economical treatment available for large scale bacterial/viral problems; fortunately, most are rarely severe. Keep in mind that viruses need fish to survive — they enter a pond via infected fish. Whereas, bacteria are present in the pond environment and severely infect fish that are stressed or mishandled. Fish secrete a protective mucus coating which helps prevent fungal and bacterial/viral infections. If this coating is damaged during the spawning process or as a result of mishandling by an angler, the fish becomes more susceptible to infection. The mucus coating is less likely to be damaged if a hook is removed while the fish is still in the water, or if the angler wets his or her hands before handling the fish and Life Cycle of the Yellow Grub Life Cycle of the Yellow Grub Illustration by Duane Westerholt.