Lepomis auritus is a warmwater species typical of temperate systems where water temperatures range 4-22°C, but is reported to prefer temperatures of 27-29°C (Froese & Casal 2017; Beauchene et al. 2014; Aho & Terrell 1986). This species has been observed in thermally impacted reservoirs where temperatures were as high as 33-35°C (Siler 1975). The mean preferred temperature and optimal growth temperature for L. auritus are closely correlated; therefore, temperatures of 25-30°C should result in maximum growth, survival, and reproduction (Aho & Terrell 1986; Beitinger & Fitzpatrick 1979). Growth and survival are expected to be reduced at temperatures less than 15°C and greater than 33°C (Aho & Terrell 1986). Lepomis auritus can be found in rocky and sandy pools of creeks, small- to medium-sized rivers, and rocky and vegetated lake margins (Page and Burr 2011). Redbreast Sunfish in Yoho Lake, New Brunswick often were captured in areas of dense, submergent vegetation or near large woody debris with substrates of silt/detritus and sand (Gautreau & Curry 2012).
Lepomis auritus is a visual predator that feeds opportunistically on juvenile fishes and aquatic and terrestrial invertebrates from the benthos and water surface (Gautreau and Curry 2012; Thorp et al. 1989; Sandlow et al. 1975). Gautreau and Curry (2012) reported that the stomach contents of L. auritus consisted of 50% amphipods, 20% Trichoptera, 11% nematodes, 9% chironomids, and 10% were juvenile Lepomis, ants, and beetles. Redbreast Sunfish in Calder Lake, NY were found to feed in higher proportions on benthic prey at dawn in comparison to their diet at dusk (Thorp et al. 1989).
Spawning occurs in spring, April – October when water temperatures are 16.8°C – 25.6°C, and tends to peak in late spring and summer (Davis 1972; Bass and Hitt 1975). However, climatic differences at different latitudes may affect the time of the spawning season’s onset and duration. In Yoho Lake New Brunswick, males move into littoral zones to build nests in late June-early July—when nearshore water temperatures approach 20°C. On average, nests in Yoho Lake were about 52 cm in diameter, 35-49 cm deep, and typically within one meter from a physical structure in the water column. Males will guard their nest once a female deposits her eggs into it (Gautreau and Curry 2012).
The two major reproductive strategies utilized by Lepomis auritus are nest-building or cuckoldry (non-nesting) (Thorp et al. 1989). Reproductive strategies can be characterized by their trade-offs. Males who devote more time and energy to nest-building and defense may enhance their access to females, however, less time and energy is devoted to foraging. Cuckoldry, a behavior that is common in male sunfishes, is when a non-nesting male intrudes a conspecific spawning between a nest-building male and a female and fertilizes the eggs. This behavior deceives the nesting male into unknowingly providing care for the brood that is not genetically his own (Gross 1979). Thorp et al. (1989) discovered that non-nesting males had fuller stomachs and consumed a greater diversity of prey items than nesting sunfish. While nesting confers a higher probability of successful mating, it is also energetically costly. Cuckoldry requires less energetic investment and improves the likeliness of food acquisition, but may limit reproductive success. Genetic analysis of these two strategies found that the nest-building male sired 90% of the progeny from 25 nests. However, 40% of the nests showed evidence of a cuckoldry, although cuckolders only accounted for <10% of the overall progeny (DeWoody et al. 1998).
Females produce an average of 3302 eggs, with a range of 322-9206 depending on their body size (Sandow et al. 1975). Lepomis auritus eggs from the Susquehanna River were on average 2.1 mm in diameter, yellow in color, and adhesive (Buynak & Mohr 1978).
When they hatch, larvae are 4.6 to 5.0 mm long, have incomplete mouths, large ovoid yolk sacs, pectoral fin buds and straight urostyles. Caudal, dorsal, anal, and pectoral fin rays develop when larvae are 7.8-8.1 mm and pelvic fin ray development begins by the time the fish is 15 mm in total length. Lepomis auritus develops darker pigmentation as it reaches its juvenile phase by 19.0 mm (Buynak & Mohr 1978). Redbreast Sunfish grow to about 60 mm within their first year and grow an additional 30 mm or so per year until age 6 (Etnier & Starnes 1993).
Lepomis auritus has a longevity of 7 years and maturity typically occurs by age 2, corresponding to 90-120 mm total length (Sammons and MacEina 2009; Etnier and Starnes 1993).
Growth of L. auritus is largely tied to environmental factors. In riverine environments, growth rates are significantly higher than in impounded environments. However, other variables such as geography, climate, and hydrology can also explain variation in growth rates (Rypel 2011; Sammons and MacEina 2009). Sammons and MacEina (2009) found that L. auritus growth was positively related to river flows with fish growth increments being significantly larger in wet years compared to dry years for fishes age 1-3 years. Flows had the greatest effect on growth in rivers that had large floodplains that were only connected to the main river channel during high flow events. High river flows likely promote increased growth rates by creating a shallow floodplain that offers more habitat with refuge from flows and greater terrestrial invertebrate food resources (Schlosser 1998).