Weight measurements are recorded by placing the fish into a small plastic container set on a portable electronic balance. Care should be taken to ensure that the balance is reasonably level and protected from the weather to minimize any error associated with determining weight measurements under field conditions. A hanging scale is required in addition to a portable balance to determine the weight of large fish that exceed the limits of the portable balance. Weight should be recorded to the nearest gram.
Weight is recorded individually for all individuals of a species that are measured for length. For those individuals of a species weighing less than 1 g, an average weight of at least 30 individuals is determined.
All fish, including those not measured and weighed, are examined for the presence of external anomalies. External anomalies are defined as the presence of externally visible skin or subcutaneous disorders, or parasites (Ohio Environmental Protection Agency, 1987) and require training to detect. The presence of external anomalies may indicate sublethal environmental stresses, intermittent stresses, behavioral stresses, or chemically contaminated substrates. External anomalies include deformities, eroded fins, lesions, tumors, diseases, and parasites.
Deformities are skeletal anomalies that affect the head, spinal vertebrae, and general body shape, and are easily detected. They can be produced by a number of factors, including toxic chemicals, viruses, bacteria, infections, and parasites. Komanda ( 1980) found that deformities were uncommon in fish populations exposed to optimal water-quality conditions.
Eroded fins are reductions in fin surface area and hemorrhaging along fin rays, which can be caused by chronic disease or parasite infestation. They are also frequently observed in areas of poor water quality, such as high water temperatures, or low di ssolved oxygen or high ammonia levels. However, eroded fins can be caused by other factors such as mechanical erosion during spawning. Hatchery-raised fish stocked in streams may also have eroded fins as a result of prolonged holding under crowded conditions in concrete-lined raceways. In addition, damaged fins or fins with irregularities may be the result of tagging studies conducted by local fish ecologists to obtain information for research or management (Wydoski and Emery, 1983).
Lesions often appear as open sores or exposed tissue and can be caused by viral and bacterial infections. Prominent bloody areas on fish are also classified as lesions. However, obvious injuries (for example, lamprey scars) should not be included unless they are lesions. Lesions can result from exposure to poor water-quality conditions.
Tumors are produced by unregulated cellular growth in tissue and are generally the result of exposure to toxic chemicals or viral infections. Some parasites can cause tumor-like