Lepomis microlophus (redear sunfish)

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Title Adult Caption Lepomis microlophus (redear sunfish); adult. From original artwork by Duane Raver Copyright PUBLIC DOMAIN - Released by the U.S. Fish and Wildlife Service. Original artwork by Duane Raver.	Adult	Lepomis microlophus (redear sunfish); adult. From original artwork by Duane Raver	PUBLIC DOMAIN - Released by the U.S. Fish and Wildlife Service. Original artwork by Duane Raver.
Title Adult male Caption Lepomis microlophus (redear sunfish); adult male, guarding eggs in a canal. Margate, Florida, USA. June, 2007. Copyright ©Ianaré Sévi-2007 - CC BY 2.5	Adult male	Lepomis microlophus (redear sunfish); adult male, guarding eggs in a canal. Margate, Florida, USA. June, 2007.	©Ianaré Sévi-2007 - CC BY 2.5

Identity

Preferred Scientific Name

• Lepomis microlophus (Günther, 1859)

Preferred Common Name

• redear sunfish

Other Scientific Names

• Pomotis microlophus Günther, 1859

International Common Names

• English: shellcracker
• Spanish: chopa caracojera; mojarra oreja roja

Local Common Names

• Denmark: rodoret solaborre

Summary of Invasiveness

L. microlophus, the redear sunfish or shellcracker sunfish, is a molluscivorous freshwater fish. It natively inhabits a wide geographic range in southwestern USA, where it is found in lentic environments with little to no flow. L. microlophus is an attractive sport fish and was widely stocked in lakes and reservoirs outside of its natural range. Stocking began in the 1920s in Michigan, later in Arizona, California and more northern states, and it can now also be found in systems in New England. L. microlophus is not considered a nuisance species and is not on any regional or national alert lists. Direct negative impacts of its colonization in western and north watersheds are not evident. Environmental impacts are in some cases the reduced density of its sister species, the pumpkinseed sunfish (L. gibbosus), due to L. microlophus' higher efficiency at consuming hard-shelled prey. The species is still stocked as a recreational fish in reservoirs. Its efficiency as a molluscivore has provided evidence of its successful application as a biocontrol species to eradicate invasive/harmful snail populations and quagga mussels.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Chordata
•             Subphylum: Vertebrata
•                 Class: Actinopterygii
•                     Order: Perciformes
•                         Suborder: Percoidei
•                             Family: Centrarchidae
•                                 Genus: Lepomis
•                                     Species: Lepomis microlophus

Notes on Taxonomy and Nomenclature

Lepomis is a mixture of the Greek words for scale (lepis) and gill cover (poma), known as the operculum. The specific name microlophus is Greek for small nape (Froese and Pauly, 2007).

Lepomis microlophus is referred to in scientific literature as the redear sunfish due to its characteristic red spot on the operculum. It is also commonly referred to the shellcracker due to its ability to crack gastropods and mollusc shells.

Description

From Mills et al. (2004), Stone (2008) and Fuller et al. (2014):

L. microlophus is a species of centrarchid fish. It is characteristically deep-bodied which means that they are elongate in the dorso-ventral ('back-to-belly') axis. L. microlophus may have darker pigmented spots on its sides with occasional cases of younger fish also exhibiting dark vertical lines. The operculum is black with a thin white border and a red (to orange in females) spot – the characteristic spot which gives its name. In comparison with other sunfish, L. microlophus has pointier pectoral fins, with the dorsal fin exhibiting 10 spines and 10-12 rays. The average length ranges between 19 and 25 cm.

Distribution

L. microlophus natively inhabits a wide geographic range in southwestern USA, from central Texas in the west to the Atlantic coast in the east. It natively occurs as far north as southern Illinois and Indiana in central USA and only as far north as South Carolina in the east (Whittier and Hartel, 1997).

It has been introduced as a sport fish to several US states, including Michigan, Indiana and California. Outside of the USA, L. microlophus has also been stocked in South Africa, Morocco and Panama (Mills et al., 1993).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

L. microlophus is native to much of southwestern USA (Whittier and Hartel, 1997). Its appeal as a sport fish has led to the spread of the species in the USA as it has been intentionally stocked north and west of its native range (Huckins et al., 2000; Fuller et al., 2014).

L. microlophus was introduced to Michigan in the 1920s, with further introductions in the 1950s and extensive stocking in 1984 and 1995, when the fish were stocked in about 45 southern Michigan lakes by the Michigan Department of Natural Resources (Huckins et al., 2000). In 1928 L. microlophus was successfully introduced to northern Indiana (stocked in lakes and streams), in the Great Lakes basin (Mills et al., 1993). The species was stocked in Arizona in 1947 and is well established in the region (Rinne, 1995). L. microlophus was initially introduced in California in the lower Colorado River in either 1948 or 1949 (Mills et al., 1993).

The status of L. microlophus in North Carolina is uncertain. Some sources consider the species as native to the state (e.g. Huckins et al., 2000), whereas Fuller et al. (2014) maintained that North Carolina lies outside of the species’ native range.

Whittier and Hartel (1997) reported the first records of L. microlophus in the state of Vermont, where it was found in two separate lakes during the US EPA’s Environmental Monitoring and Assessment Program in 1991. The authors speculated that its origin could stem from unauthorized stocking.

L. microlophus has also been stocked in South Africa, Morocco and Panama (Mills et al., 1993).

Introductions

Risk of Introduction

All cases of L. microlophus introduction have been due to intentional stocking for sport fishing purposes. Therefore any further introduction is likely to be related to stocking, or the unaided spread of the species through interconnected water systems in individual watersheds.

Habitat

L. microlophus is predominantly a warm water fish (Mills et al., 2004), occurring in both riverine and lake environments (Whittier and Hartel, 1997; Froese and Pauly, 2007). It is predominantly found in littoral areas, with slow flow rates and high vegetation densities (Fuller et al., 2014). However, L. microlophus is very tolerant to temperature and salinity conditions and therefore inhabit a wide range of habitats. It can be found in estuaries, where its high salinity tolerance provides them with a competitive advantage.

Twomey et al. (1984) reported that L. microlophus inhabiting riverine systems were usually found in areas with no noticeable flow, in bays protected from the main channel. Studies summarized therein provided evidence that adult L. microlophus tend to be found in deeper waters, close to the edge of the vegetated zone, moving towards shallower areas close to the shore during spawning. Despite its wide range of habitat, Twomey et al. (1984) reported that the fish does best in lakes, with their numbers depending on the amount of vegetation cover.

Aquatic vegetation provides protection as well as a food source for invertebrate populations on which L. microlophus feed (Twomey et al., 1984; Martin et al., 1992). Martin et al. (1992) observed closely interrelated dynamics between L. microlophus, aquatic vegetation and invertebrate densities in experimental trials (see Nutrition). 

Habitat List

Biology and Ecology

Genetics

Roberts (1964) reported a diploid chromosome number of 48 for L. microlophus. The different North American Lepomis species are known to hybridize, mainly because of their geographic overlap and concurrent spawning season (Avise and Saunders, 1984). The different species have the ability to produce 55 different hybrid combinations, 20 of which have been observed in nature and captivity, some of which are not sterile and can successfully reproduce (Avise and Saunders, 1984).

Reproductive Biology

The start and duration of the spawning period for L. microlophus in the USA varies with geographical location (Twomey et al., 1984). The observed spawning periods are concentrated in the spring and the summer months between April and August (Mills et al., 2004). In warmer regions, such as Florida, L. microlophus has been observed to spawn between February and October, whereas in colder regions the spawning period is much shorter (Twomey et al., 1984).

Spawning temperature was reported to range from 20 to 21°C by Stone (2008) and 21 to 24°C by Mills et al. (2004).

Spawning habitat, nest depth and location also vary and show no consistent pattern in the species’ reproductive biology. Spawning and nesting can occur in gravel, sandy or clayey sediment bottoms (Twomey et al., 1984; Mills et al., 2004). The nests are fanned of debris and usually located in sheltered places amongst, or on the edges of, vegetation and large woody debris. Nests have been spotted in extremely shallow regions between 5 and 10 cm and deeper ranges between 4 to 6 m . Males remain with the eggs, fanning and guarding the nest for about 6 to 10 days until they hatch. Observations show that the optimal hatching temperature which results in the highest hatching percentage is between 21 and 24°C (Twomey et al., 1984).

Longevity

L. microlophus has a lifespan of about 7 years (Mills et al., 2004), with a maximum reported age of 8 (Twomey et al., 1984). It matures between 1 and 2 years, although reproductive maturity is attributed to size rather than age and can be dependent on the overall age distribution within a fish population (Twomey et al., 1984).

Nutrition

L. microlophus is a specialized molluscivorous species (Minckley, 1982; VanderKooy et al., 2000; Wang et al., 2003; Fuller et al., 2014). The presence of upper and lower pharyngeal teeth inside the mouth provide it with the ability to crush molluscs (Minckley, 1982; Lauder, 1983; French III, 1993). Its shell crushing ability has also been connected to the consumption of gastropods (snails), first observed in Martin et al. (1992). L. microlophus’ affinity towards snails has since been extensively documented (VanderKooy et al., 2000; Wang et al., 2003; Ledford and Kelly, 2006; Noatch and Whitledge, 2011).

VanderKooy et al. (2000) observed that large L. microlophus predominantly focus on hard-shelled prey such as ostracods, hydrobiid snails and mussels throughout the entire year. In the same field investigation it was observed that smaller fish tended to also consume zooplankton, amphipods, chironomid and certopongonid larvae and cladocerans, with varied distributions depending on the season. Similar organism remains were found in the stomach contents of L. microlophus predominantly feeding on quagga mussels (Wong et al., 2013).

It has been observed that L. microlophus exhibits a higher (ca. 2x) crushing efficiency of hard-shelled prey than competing species such as the pumpkinseed, L. gibbosus (Huckins, 1997). The crushing efficiency is due to the strength differences between the species, which has led  to a shift in the feeding assemblages of the species when both are present, resulting in a higher consumption of hard-shelled prey by L. microlophos (Huckins, 1997). A detailed description of the branchial musculature of sunfish species (and the singularities in the separate species) is presented in Lauder (1983).

Natural Food Sources

Climate

Latitude/Altitude

Water Tolerances

Natural Enemies

Pathway Causes

Impact Summary

Economic Impact

Negative economic impacts directly related to the stocking of L. microlophus have not been reported in literature. 

Environmental Impact

The widespread stocking of L. microlophus has led to its establishment in watersheds outside of its native range, where it overlaps with other fish species that fill the same tropic niche in those areas. The majority of the impacts associate with L. microlophus are competitive interactions due to a shared food source, as well as due to its foraging habits. None of these impacts have been documented as a nuisance and it continues to be stocked for sport fishing.

Impact on Habitats

Martin et al. (1992) experimentally tested the direct and indirect effects of fish on macroinvertebrate communities. The results showed that predation of gastropods by sunfish reduced the population of snails in aquatic systems. Snails act as grazers for aquatic flora such as macrophytes (Martin et al., 1992); therefore, L. microlophus’ direct consumption of snails may have an indirect effect on the aquatic fauna (Ruiz et al., 1999). Experimental systems with L. microlophus population showed a marked increase in macrophyte density (Martin et al., 1992). However, experimental trials were conducted under high fish abundances and the results do not necessarily translate for regions with lower L. microlophus densities, which are observed in natural systems where the fish has been introduced (Ruiz et al., 1999). 

Impact on Biodiversity

One of the US regions most affected by the introduction of non-native fish species is California. Out of California’s 133 documented species of fish, 38% have been introduced and are not native to the region (Moyle, 1976). Because of California’s unique geological makeup 30% of its native fish species are found in no other state, and the proliferation of introduced species such as L. microlophus puts pressures on these endemic populations and could push them towards becoming endangered (Moyle, 1976).

Because of L. microlophus’ higher specialization for hard-shelled prey compared to pumpkinseed sunfish (Lepomis gibbosus), it has the potential to outcompete the latter (Huckins et al., 2000). Huckins (1997) observed that L. microlophus, in the presence of L. gibbosus, consumed more hard-shelled prey than their counterpart. Analyses in Huckins (1997) showed that the crushing strength exhibited by L. microlophus was significantly greater than that for L. gibbosus, likely contributing to its higher effectiveness as a molluscivore.

Lentic systems where both L. microlophus and L. gibbosus are present exhibit lower L. gibbosus population densities than expected, as well as a reduced molluscivory in the L. gibbosus population (Huckins, 1996). These negative effects were confirmed in Huckins et al. (2000), as well as the impacts of L. microlophus introduction on snail populations (Martin et al., 1992; Huckins, 1996; Huckins et al., 2000). Huckins et al. (2000) observed that the L. gibbosus population declined on average by 56% in lakes where L. microlophus were introduced, and snail biomass declined by almost 70%. 

Social Impact

L. microlophus is a sought-after recreational fish for sport fishing (Mills et al., 2004), which accounts for its popularity and extensive stocking. Negative economic impacts directly related to the stocking of L. microlophus have not been reported in literature. 

Risk and Impact Factors

Impact mechanisms

• Competition

Impact outcomes

• Threat to/ loss of native species

Invasiveness

• Abundant in its native range
• Benefits from human association (i.e. it is a human commensal)
• Has a broad native range
• Highly adaptable to different environments
• Highly mobile locally
• Is a habitat generalist

Likelihood of entry/control

• Highly likely to be transported internationally deliberately

Uses

Economic Value

L. microlophus is stocked for sport fishing purposes as a recreational fish.         

Environmental Services

L. microlophus has been shown to successfully mitigate an invasive quagga mussel (Dreisena rostriformis bugensis) population in a lake system in southwest USA (Wong et al., 2013). Wong et al. (2013) observed that L. microlophus stocked at high densities (0.42 fish/m3) reduced the quagga mussel population density by 90% within 3 months of stocking. The use of L. microlophus as a biocontrol agent for quagga mussels avoids the implementation of other invasive/nuisance species, such as black carp (Mylopharyngodon piceus).

L. microlophus has also been observed to consume significant amounts of zebra mussels (Dreissena polymorpha), with some specimens exhibiting a dietary composition of 100% (Magoulick and Lewis, 2002). Unfortunately, their implementation as a biocontrol agent for zebra mussels is projected to be unsuccessful due to the zebra mussels’ prolific reproduction rates (Magoulick and Lewis, 2002).

Experimental studies have provided evidence that shows that L. microlophus can be implemented as a biocontrol agent for invasive ramshorn snails (Ledford and Kelly, 2006). L. microlophus have also been observed to reduce snail densities in aquaculture systems, where snails are carriers of harmful diseases and can affect the health of cultivated fish (Noatch and Whitledge, 2011). However, snail populations have been observed to rebound; therefore, Noatch and Whitledge (2011) recommended the use of biocontrol methods in conjunction with other attenuation methods (such as chemical control) to achieve higher effectiveness.

Uses List

Environmental

• Biological control

Similarities to Other Species/Conditions

L. microlophus is often mistaken for the pumpkinseed sunfish, L. gibbosus. Huckins et al. (2000) refered to them as ‘sister species’. Although both species of sunfish look very similar, they can be differentiated by the colour of the dorsal fin, body colouring and the ear flap (Whittier and Hartel, 1997); L. gibbosus has wavy lines on their cheeks and operculum (Whittier and Hartel, 1997), whereas L. microlophus has no specific ‘conspicuous’ patterns on the lateral sides of the (Mills et al., 2004).

Prevention and Control

As all of the cases of L. microlophus introduction have been connected to stocking for recreational fishing purposes, to avoid the spread of the species into new ranges the stocking of the fish should be restricted. The removal of the maximum allowable catch for anglers could control L. microlophus populations in areas where it is a concern. However, it should be noted that L. microlophus is not considered a nuisance species and is not on any regional or national alert lists. Direct negative impacts of its colonization in western and north watersheds are not evident.

Chemical Control

Antimycin in the Fintrol-5 formulation can be used for selective thinning of L. microlophus in overcrowded ponds (Burress and Luhning, 1969).

Increasing CO2 concentrations in water can result in fish sedation and provides a simple methods for removal of sedated fish. However, this method is reported to be minimally selective and can result in a lot of by-catch (Fuller et al., 2014). 

References

Aquatic Parasite Observatory, 2013. Aquatic Parasite Observatory. Boulder Colorado, USA: University of Boulder Colorado.

Avise JC, Saunders NC, 1984. Hybridization and introgression among species of sunfish (Lepomis): analysis by mitochondrial DNA and allozyme markers. Genetics, 108(1):237.

Buck DH, 1956. Effects of turbidity on fish and fishing. Oklahoma, USA: Oklahoma Fisheries Research Laboratory.

Burress RM, Luhning CW, 1969. Use of antimycin for selective thinning of sunfish populations in ponds. Investigations in Fish Control 28: Bureau of Sport Fisheries and Wildlife. Washington, DC, USA: US Fish and Wildlife Service.

Conte FS, Waldvogel JB, Vaught TS, 2001. Fish stocking strategies for largemouth bass in recreational ponds and lakes. California Aquaculture, ASAQ-C14.

French IIIJR, 1993. How well can fishes prey on zebra mussels in eastern North America? Fisheries, 18(6):13-19.

Froese R, Pauly D, 2007. FishBase. http://www.fishbase.org

Fuller P, Jacobs G, Cannister M, Larson J, Fusaro A, Makled TH, Neilson M, 2014. Lepomis microlophus. Gainesville, Florida, USA: USGS Nonindigenous Aquatic Species Database. http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=390

Huckins CJF, 1996. DPhil Thesis. Lansing, USA: Michigan State University.

Huckins CJF, 1997. Functional linkages among morphology, feeding performance, diet, and competitive ability in molluscivorous sunfish. Ecology, 78(8):2401-2414.

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Mills EL, Leach JH, Carlton JT, Secor CL, 1993. Exotic species in the Great Lakes - a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research, 19(1):1-54. http://sgnis.org/publicat/papers/19p1.pdf

Mills TJ, Bratovich P, Olson D, Atherston M, Niggemyer A, O'Connell A, Riggs K, Ellrott B, Vodopals K, 2004. Matrix of life history and habitat requirements for Feather River fish species: Redear Sunfish. Oroville Facilities P-2100 Relicensing, California, USA: State of California Department of Water Resources.

Minckley W, 1982. Trophic interrelations among introduced fishes in the lower Colorado River, southwestern United States. California Fish and Game, 68(2):78-89.

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Noatch MR, Whitledge GW, 2011. An evaluation of hydrated lime and predator sunfish as a combined chemical-biological approach for controlling snails in aquaculture ponds. North American Journal of Aquaculture, 73(1):53-59. http://www.informaworld.com/smpp/content~db=all~content=a933049383~frm=titlelink

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Rinne JN, 1995. The effects of introduced fishes on native fishes: Arizona, southwestern United States, Protection of aquatic biodiversity. In: Proceedings of the World Fisheries Congress, Theme 3. 149-159.

Roberts FL, 1964. A chromosome study of twenty species of centrachidae. Journal of Morphology, 115(3):401-417.

Ruiz GM, Fofonoff P, Hines , AH, Grosholz ED, 1999. Non-indigenous species as stressors in estuarine and marine communities: assessing invasion impacts and interactions. Limnology and Oceanography, 44(3):950-972.

Starnes WC, Odenkirk J, Ashton MJ, 2011. Update and analysis of fish occurrences in the lower Potomac River drainage in the vicinity of Plummers Island, Maryland. Contribution XXXI to the natural history of Plummers Island, Maryland. Proceedings of the Biological Society of Washington, 124(4):280-309.

Stone NM, 2008. Forage fish - introduction and species. Publication No. 140. United States Department of Agriculture, USA: Southern Regional Aquaculture Center.

Twomey KA, Gebhart , G, Maughan , OE, Nelson , PC, 1984. Habitat suitability index models and instream flow suitability curves: Redear sunfish. FWS/OBS-82/10.79. Washington, DC, USA: US Fish and Wildlife Service, 29.

VanderKooy KE, Rakocinski CF, Heard , RW, 2000. Trophic relationships of three sunfishes (Lepomis spp.) in an estuarine bayou. Estuaries, 23(5):621-632.

Wang HP, Hayward RS, Whitledge GW, Fischer SA, 2003. Prey-size preference, maximum handling size, and consumption rates for redear sunfish Lepomis microlophus feeding on two gastropods common to aquaculture ponds. Journal of the World Aquaculture Society, 34(3):379-386.

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Wong WH, Gerstenberger SL, Hatcher MD, Thompson DR, Schrimsher D, 2013. Invasive quagga mussels can be attenuated by redear sunfish (Lepomis microlophus) in the Southwestern United States. Biological Control, 64(3):276-282. http://www.sciencedirect.com/science/article/pii/S1049964412002526

Links to Websites

Principal Source

Draft datasheet under review

Contributors

19/12/14 Original text by:

Adrian Mellage, consultant, Germany

Distribution Maps

• = Present, no further details
• = Evidence of pathogen
• = Widespread
• = Last reported
• = Localised
• = Presence unconfirmed
• = Confined and subject to quarantine
• = See regional map for distribution within the country
• = Occasional or few reports

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