Silver perch, continued 



coastal lagoons in the spring to spawn (Gunter 1945, 

 Miller 1964, De Sylva 1965). Juveniles move into the 

 shallow inner bays (Gunter 1945), and then, as they 

 grow, move back to deeper bay and offshore water, 

 especially during winter months (Killam et al. 1992). 



Reproduction 



Mode : This species has separate male and female 

 sexes (gonochoristic). Fertilization is external, by 

 broadcast of milt and roe into the water column 



Spawning : As with most of the drums, sounds pro- 

 duced by specialized muscles inserted at the swim 

 bladder wall are believed to have a purpose in the 

 spawning activity. Spawning probably occurs in the 

 deeper waters of primary bays and passes (Hildebrand 

 and Cable 1 930, Gunter 1 945, Springerand Woodburn 

 1 960, Thomas 1 971 , Sabins and Truesdale 1 974, Mok 

 and Gilmore 1983), but may also occur offshore to 

 some extent since eggs have been collected there 

 (Hildebrand and Cable 1930, Wang and Raney 1971, 

 Christmas and Waller 1973). The reported season is 

 May to September in northern Florida (Reid 1 954) with 

 similar times in Texas and Louisiana (Gunter 1945, 

 Wagner 1973, Sabins and Truesdale 1974). Some 

 year-round spawning appears to occur in the estuaries 

 of southern Florida (Killam et al. 1992). Spawning 

 peaks may occur in spring and late summer, but may 

 vary with location (Christmas and Waller 1973, Lee et 

 al. 1 980). Based on the presence of larval silver perch 

 in the northern Gulf of Mexico, it can be inferred that 

 spawning occurs March through October, with peak 

 from April to August (Ditty et al. 1988). 



Fecundity : A Florida study examined 1 1 females rang- 

 ing in size and weight from 1 39.3 to 1 77.4 mm SL and 

 55.3 to 123.8 g, respectively, and determined their 

 mean fecundity to be 90,407 eggs (Schmidt 1993). 



Growth and Development 



Egg Size and Embryonic Development : Reported egg 

 sizes range from 0.59 to 0.88 mm total diameter (mean 

 0.69-0.83 mm). They are buoyant, transparent, and 

 possess one relatively large oil globule (Kuntz 1914, 

 Joseph et al. 1 964, Ditty and Shaw 1 988). Embryonic 

 development is oviparous. 



Age and Size of Larvae : Yolk sac larvae hatch at 1 .5- 

 1 .9 mm TL (Welsh and Breder 1 923). Ditty and Shaw 

 (1 994) report incubation times of 1 8 hours at 27°C, and 

 40-50 hours at 20°C. Two days after hatching the yolk 

 sac is completely absorbed when larvae measure 2.5 

 to 2.8 mm TL (Kuntz 1914, Welsh and Breder 1923). 



Juvenile Size Range : The juvenile stage is attained at 

 a total length (TL) of about 10 - 12 mm (Kuntz 1914, 

 Ditty and Shaw 1 994). By 1 5 mm, their fin rays are fully 



developed, and their body is lightly pigmented except 

 in the thoracic region (Wang and Kernehan 1 979). By 

 30 mm SL, juveniles essentially have the form of an 

 adult (Johnson 1978). Juveniles have growth rates 

 around 15 mm/month from May to November 

 (Hildebrand and Cable 1930, Christmas and Waller 

 1973). 



Age and Size of Adults : The silver perch reaches 

 sexual maturity during its first year in the warmer, more 

 southern parts of its range (Schmidt 1 993). In northern 

 areas of its range where water temperatures are cooler 

 for longer periods of time, growth is slower and maturity 

 may not occur until the second year (Hildebrand and 

 Cable 1 930, Welsh and Breder 1 923). A study in south 

 Florida found maturity in both males and females 

 occurred at about 95 mm SL (Schmidt 1993). Maxi- 

 mum size seldom exceeds 240 mm TL (Welsh and 

 Breder 1 923). This fish may live up to 6 years (Welsh 

 and Breder 1923, Lee et al. 1980). 



Food and Feeding 



Trophic Mode : The silver perch is primarily a benthic 

 carnivore, feeding mostly on crustaceans, and to a 

 lesser degree, polychaetes and nematodes (Darnell 

 1958, Springer and Woodburn 1960, Diener et al. 

 1974, Gosselink 1984, Killam et al. 1992, Schmidt 

 1993). 



Food Items : Diet varies seasonally and with develop- 

 ment (Schmidt 1993). Larvae and small juveniles 

 consume mostly zooplankton (copepod and fish lar- 

 vae) (Hildebrand and Cable 1 930, Darnell 1 958). Small 

 juveniles (7 to 20 mm TL) consume invertebrates such 

 as copepods, ostracods, cladocera, schizopods, am- 

 phipods, mysids, and annelids. At 50 to 80 mm TL, they 

 feed increasingly on annelids, larger crustaceans (such 

 as shrimp), molluscs, chironomidae larvae. Larger 

 juveniles and adults also consume small fishes (pin- 

 fish, anchovies, gobies, silver perch) and crabs, in 

 addition to these other food items (Darnell 1958, 

 Springer and Woodburn 1960, Diener et al. 1974, 

 Levine 1980, Gosselink 1984, Killam et al. 1992, 

 Schmidt 1 993). Largerfish tend to have a more diverse 

 diet (Schmidt 1993). 



Biological Interactions 



Predation : Little information is available concerning 

 predation on this species, but considering its abun- 

 dance, it is a likely prey item for numerous species of 

 piscivorous fish (Killam et al. 1992). Reported preda- 

 tors include spotted seatrout and king mackerel 

 (Scomberomorus cavalla) (Kemp 1949, Darnell 1958, 

 Killam etal. 1992). 



Factors Influencing Populations : Distribution and abun- 

 dance may be influenced by a variety of water quality 



249 



