masses, but these should not be considered tumors. Parasite masses can be squeezed and broken between the thumb and forefinger whereas tumors are firm and not easily broken.
Black spot is a disease caused by a parasite that can be identified by the presence of small black cysts on the skin and fins. Severe infections may cause spinal deformities or secondary infections. In some areas, habitat degradation accompanying agricultural and urban development has been shown to be associated with increased incidence of black spot (Steedman, 1991).
"Ich" is the common term for the disease caused by the protozoan, Ichthyophthirus multifilis. This organism can be identified by the presence of white spotting on the external surface of the fish. This disease can occur in wild fish populations but is more common in hatchery-raised fish.
The anchor worm (Lernaea spp.) is a parasite that can be identified by the presence of a slender, worm-like body buried in the flesh of a fish. A small, characteristic sore is left after the anchor worm detaches. Attachment sites are included even if the worm is no longer present. If the attachment site becomes infected, it should also be recorded as a lesion.
Leeches are green to brownish segmented worms that can be identified by the presence of two suckers (one on each end) and the ability to contract or elongate their bodies. They may occur anywhere on the external surface of the fish.
The presence of eye anomalies should also be noted. Eye anomalies include discoloration of the lens, blindness, missing eyes, and "popeye" disease. Parasites can attack the lens of the eye causing the eye to deteriorate. Popeye disease is identified by the presence of bulging eyes and is generally caused by gas accumulation in areas where the water is gas supersaturated. It can also occur as the result of fluid accumulation behind the eyes due to viral infection or parasites.
After examination of the fish for external anomalies, the fish is placed in a container of ambient water and allowed to recover from the effects of the anesthetic before release. Fish should be released downstream of the sampling reach so as to reduce the potential for re-sampling, and thereby bias the sample. Not all fish are released at a site; some fish must be fixed and preserved.
Fixing and preserving of specimens are required for fish that cannot be taxonomically identified in the field and for voucher specimens (representatives of specimens collected from each sampling reach). The recommended fixative is a formaldehyde solution known as formalin. When formaldehyde, a gas, is dissolved in water to maximum saturation, it produces formalin, which is about 37- to 39-percent formaldehyde by weight. Formalin is considered a hazardous material and must be handled with care. It is poisonous if ingested, and exposure to small amounts can create such symptoms as a burning sensation in the eyes and nose, watering eyes, headaches, and a sore throat. Working with formalin should be done only in well-ventilated areas. Skin can become sensitized to formalin exposure,