Spotted Bass are most common in moderately sized, clear, low gradient rivers and reservoirs. In streams they spend most of their time hiding in pools, avoiding riffles or backwaters with heavy plant growth. Reservoir populations stay along steep rocky banks towards the upstream end of the reservoir. During the summer they can be found in temperatures between 24°C and 31°C, and despite a low tolerance for brackish water they but have been found in salinities up to 10 ppt. Juveniles can easily be seen schooling in shallow areas close to shore, but adults are more solitary and spend most of their time 1-4 m deep and or even further down when temperatures equalize in winter. Like most fish the Spotted Bass’s diet expands as they get older. Fry focus mostly on zooplankton and small insects, moving on to crustaceans and larger aquatic insects as juveniles. Individuals between 75 mm and 150 mm feed on aquatic insects, fish, crayfish, and terrestrial insects, eventually focusing most of their energy on crayfish.
Maturity is reached in the second or third year and spawning occurs when temperatures reach 15-18°C, continuing until temperatures reach 22-23°C in early June. Males move to shallow water in March and early April, where they construct nests 40-80 cm in diameter. Lake nests are built in areas 0.5-4.5 m deep with large rocks and rubble or gravel, while nearly any area with low current can be used in rivers. These nests may be built close together but they are not colonial and males will defend the nests as vigorously against other males as they would against predators. Spawning is initiated by a female repeatedly swimming by a male’s nest, changing colors, and keeping her head down in a mating posture. Eventually the pair circle the nest with the male nipping at the female, and the female occasionally rubbing her abdomen on the nest floor. The pair will then settle into the nest and release their eggs and milt simultaneously. Spotted Bass are mostly monogamous but some males may have more than one nest. Each female will lay 2,000-14,000 eggs per nest. The male will tend to and defend the nest for up to 4 weeks, until the fry disperse at 30 mm TL. Growth varies with habitat, with warmwater reservoirs supporting the highest growth and cold streams the slowest. On average, however, individuals reach 65-170 mm TL their first year first year and 245-435 mm TL in their fourth. Few live longer than 4-5 years and the largest recorded individual for California was 450 mm.
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