Hardhead catfish, continued 



Substrate : Juveniles and adults have mostly been 

 found over bottoms of mud, oyster beds, sand, shell, 

 sandy mud, silt, and sand with shell (Lee 1937, Reid 

 1955, Gunter and Hall 1965, Miller 1965, Swingle 

 1971). Juveniles have been reported not to use 

 seagrass beds (Zimmerman 1969), although adults 

 have been found in areas with seagrass and detritus 

 substrates. 



Physical/Chemical Characteristics : 

 Temperature - Eggs and Larvae: Eggs have been 

 observed in both laboratory and field studies over a 

 temperature range of 28.0° to 34.0°C (Gunter 1945, 

 Ward 1 957, Bryan 1 971 , Perret et al. 1 971 , Wang and 

 Raney 1971, Christmas and Waller 1973). Yolk sac 

 larvae have been observed in the field from 15.0° to 

 34.9°C (Gunter 1945, Christmas and Waller 1973, 

 Tarver and Savoie 1976). 



Temperature - Juveniles and Adults: Both juveniles 

 and adults have been observed in the field from 5.0° to 

 39.0°C (Hellier 1962, Miller 1965, Perret et al. 1971, 

 Swingle 1 971 , Wang and Raney 1 971 , Dunham 1 972, 

 Franks et al. 1972, Christmas and Waller 1973, 

 Gallaway and Strawn 1 974, Perret and Caillouet 1 974, 

 Juneau 1975, Tarver and Savoie 1976, Barrett et al. 

 1978, Benson 1982). The maximum acceptable tem- 

 perature is probably 37.0°C, with 39.0°C being close to 

 the upper lethal limit for this species (Gallaway and 

 Strawn 1974). The preferred temperature range ap- 

 pears to be 19.0° to 25.0°C (Benson 1982). 



Salinity - Eggs and Larvae: Eggs have been observed 

 in both laboratory and field studies in salinities ranging 

 from 1.8 to 36.4%o (Gunter 1945, Ward 1957, Bryan 



1971, Perret et al. 1971, Wang and Raney 1971, 

 Christmas and Waller 1973). Yolk sac larvae have 

 been collected from brooding males in salinities rang- 

 ing from 2.0 to 36.0%o (Bryan 1 971 , Perret et al. 1 971 , 

 Wang and Raney 1971, Christmas and Waller 1973, 

 Cornelius 1984). 



Salinity - Juveniles and Adults: Free swimming juve- 

 niles have been collected from to 56% salinity. They 

 are reported to prefer <10%o (Perret etal. 1971, Wang 

 and Raney 1 971 , Christmas and Waller 1 973, Cornelius 

 1984). Adults are euryhaline, and are common from 

 0.0 to 45% (Gunter 1 945, Gunter 1 947, Gunter 1 956, 

 Simmons 1 957, Hoese 1 960, Hellier 1 962, Miller 1 965, 

 Bryan 1971, Perret 1971, Swingle 1971, Dunham 



1972, Frank et al. 1972, Christmas and Waller 1973, 

 Perret and Caillouet 1974, Swingle and Bland 1974, 

 Juneau 1975, Tarver and Savoie 1976, Swift et al. 

 1 977, Barrett et al. 1 978, Cornelius 1 984), but occur in 

 salinities as high as 60%o (Simmons 1 957). They have 

 been reported to show some preference for 15.0 to 

 30.0% o salinities, and are increasingly less common 



below 1 5%o (Gunter 1 945, Perret et al. 1 971 , Swingle 

 1 971 , Franks et al. 1 972, Christmas and Waller 1 973, 

 Swingle and Bland 1974). 



Dissolved Oxygen: The hardhead catfish has been 

 collected in waters with a dissolved oxygen (DO) 

 content range of 2.7 to 11.1 parts per million (ppm) 

 (Bryan 1971, Barrett etal. 1978). It is sometimes found 

 in habitats characterized by low DO (Benson 1982). 



Movements and Migrations : The hardhead catfish gen- 

 erally decreases in abundance in bays and estuaries 

 along the northern Gulf of Mexico and Texas coast 

 during fall and winter as it moves to deeper waters of 

 the Gulf or sometimes within an estuary system to 

 overwinter. It then returns to shallows during spring 

 and summer (Gunter 1945, Miller 1965, Swingle 1971, 

 Franks et al. 1972, Landry and Strawn 1973, Steele 

 1985). Older age class fish are reported to migrate 

 while many of the younger ones remain in the bays 

 (Swingle 1971). Migration to the Gulf can begin as 

 early as September with the lowest numbers in bay 

 systems occurring from Novemberto February (Swingle 

 1 971 , Wagner 1 973). Abundance increases with tem- 

 perature (Wagner 1 973, Tarver and Savoie 1 976) with 

 returns to the bays and estuaries beginning from March 

 to April. Peak abundance is observed from April and 

 May to as late as October along with a high influx of 

 young-of-the-year fish (Chambers and Sparks 1959, 

 Arnold et al. 1960, Hellier 1962, Hoese et al. 1968, 

 Zimmerman 1969, Perret et al. 1971, Christmas and 

 Waller 1 973, Wagner 1 973, Perret and Caillouet 1 974, 

 Juneau 1975, Chittenden and McEachron 1976, Ju- 

 neau and Pollard 1981, Sheridan 1983, Cornelius 

 1984). Migration may be triggered by photoperiod 

 (Steele 1984, Steele 1985). 



Reproduction 



Mode : This species has separate male and female 

 sexes (gonochoristic), and fertilization occurs exter- 

 nally. Fertilized eggs and post-hatch larvae are mouth- 

 brooded by adult males. 



Spawning : In the Gulf of Mexico, spawning takes place 

 from May to September in waters 0.6 to 1 .2 m deep. It 

 occurs in shallow waters of secondary and primary 

 bays, and Gulf inlets (Lee 1937, Gunter 1945, Gunter 

 1 947, Reid 1 955, Ward 1 957, Kelley 1 965, Bechtel and 

 Copeland 1970, Bryan 1971, Wagner 1973). Spawn- 

 ing may also occur in nearshore areas of the Gulf of 

 Mexico. Although no spawning has been observed in 

 this area, ripe females with large ovarian eggs have 

 been taken there in 21 .9 to 27.4 m depths during July 

 (Hildebrand 1 954). Eight young with yolk sacs whose 

 total lengths (TL) were approximately 45 mm were 

 collected in the surf on Galveston Island in July (Pattillo 

 pers. observ.). Furthermore, the absence of adults has 



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