Sheepshead minnow, continued 



1960, Schimmel and Hansen 1974, Hardy 1978). 



Age and Size of Larvae : Newly hatched larvae have a 

 total length (TL) of 4 mm. The yolk is relatively large, 

 and the dorsal and ventral fin folds are continuous. 

 Larvae are slightly yellowish in color and the posterior 

 half of their body is marked by lighter and darker 

 vertical bands. At five days after hatching the yolk is 

 almost completely absorbed and larvae are >5 mm TL. 

 The general color is still yellowish with vertical bands 

 slightly more conspicuous. On the sixth day, with the 

 larvae averaging 8 mm in length and about 4 mg in 

 weight, they begin active free swimming (Usher and 

 Bengtson 1981). At 9 mm many adult characters are 

 apparent. The vertical bands are present, but not fully 

 developed. Individuals are considered juveniles be- 

 ginning at 12 mm (Kuntz 1914, Hildebrand 1919, 

 Hildebrand and Schroeder 1 928, Schimmel and Hansen 

 1974). 



Juvenile Size Range : During the juvenile life stage, the 

 back becomes markedly elevated, the body depth 

 proportionally greater, and the caudal fin more rounded 

 than in the adult. Coloration is quite characteristic, 

 although the general color is lighter in the adult. Juve- 

 niles reach maturity in vitro at 3 months with sex 

 dichromatism and ripe females occurring at 27 mm 

 (Kuntz 1914, Schimmel and Hansen 1974). A field 

 study in Louisiana observed growth to be about 5 mm/ 

 month from March through October (Ruebsamen 1972). 



Age and Size of Adults : Reported size averages for 

 each sex in Texas are 45.0 mm TL for males, and 46.5 

 mm TL for females (Simpson and Gunter 1 956). The 

 largest published size is 93 mm (Gunter 1945). 



Food and Feeding 



Trophic Mode : The sheepshead minnow is a primary 

 consumer, and is often termed herbivorous, 

 detritivorous, and, infrequently, larvivorous and om- 

 nivorous. 



Food Items : Diet principally consists of plant material, 

 diatoms and other algae, detritus, amphipods, copep- 

 ods, and mosquito larvae and pupae. The remains of 

 insects, fish, sponge, annelid fragments, and pelecy- 

 pods have also been reported. Sand and mud are also 

 conspicuous stomach contents, suggesting benthic 

 feeding (Hildebrand and Schroeder 1 928, Gunter 1 950, 

 Simpson and Gunter 1956, Springer and Woodburn 

 1960, Harrington and Harrington 1961, Martin 1970, 

 Odum 1 971 , Ruebsamen 1 972, Schimmel and Hansen 

 1974, Subrahmanyam and Drake 1975, Levine 1980, 

 Perschbacher and Strawn 1986). 



Biological Interactions 



Predation : Known fish predators include spotted 

 seatrout, Atlantic croaker, and red drum (Gunter 1 945, 

 Darnell 1958). Because they often occupy shallow 

 water marsh habitat, sheepshead minnows are prey 

 for several species of wading birds (Frederick and 

 Loftus 1993). 



Factors Influencing Populations : This species has the 

 ability to tolerate a broad range of environmental 

 parameters, allowing it to survive under extreme con- 

 ditions in marginal shallow water habitats that may be 

 devoid of other fish species (Shipp 1986). The onset 

 of cooler water temperatures can initiate burrowing or 

 movementto deeper, warmer waters during the fall and 

 winter. 



References 



Blair, W.F., A.P. Blair, P. Brodkorb, F.R. Cagle, and 

 G.A.Moore. 1968. Vertebrates of the United States, 

 2nd ed. McGraw-Hill, Inc., New York, 616 p. 



Breder, CM., Jr. 1959. Studies on social groupings in 

 fishes. Bull. Am. Mus. Nat. Hist. 117:394-481. 



Breuer, J. P. 1957. An ecological survey of Baffin and 

 Alazan Bays, Texas. Publ. Inst. Mar. Sci., Univ. Texas 

 4(2):134-155. 



Christmas, J.Y., and R.S. Waller. 1973. Estuarine 

 vertebrates, Mississippi, In Christmas, J.Y. (ed.), Co- 

 operative Gulf of Mexico Estuarine Inventory and Study, 

 Mississippi. Gulf Coast Res. Lab., Ocean Springs, MS, 

 p. 320-406. 



Cornelius, S.E. 1984. An ecological survey of Alazan 

 Bay, Texas, Vol. 1. Caesar Kleberg Wildl. Res. Inst. 

 Tech. Bull. No. 5, Texas A&l Univ., Kingsville, TX, 163 



P- 



Couch, J. A., and L.A. Courtney. 1987. N- 

 Nitrosodiethylamine-induced hepatocarcinogenesis in 

 estuarine sheepshead minnow (Cyprinodon 

 variegatus): neoplasms and related lesions compared 

 with mammalian lesions. J. Natl. Cancer Inst. 79:297- 

 321. 



Darnell, R.M. 1958. Food habits of fishes and larger 

 invertebrates of Lake Pontchartrain, Louisiana, an 

 estuarine community. Publ. Inst. Mar. Sci., Univ. 

 Texas 5:353-416. 



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