blue catfishes measuring 9.5 to 20 cm (3.8 to 8 in) 

 total length. Darnell (1958) concluded that, in nearby 

 Lake Ponchartrain, blue catfish up to 10 cm (4 in) 

 total length fed mostly on zooplankton (calanoid 

 copepods, mysid shrimps, isopods and amphipods), 

 while older juvenUes measuring up to 24 cm (9.6 in) 

 total length fed more heavily on small benthic organ- 

 isms including surface and burrowing forms (amphi- 

 pods, clams, snails, annelids, isopod and aquatic 

 beetles). In the fresher waters of the Atchafalaya 

 Basin, amphipods, midge larvae and copepods were 

 the most common food items of young channel 

 catfish measuring from 3 to 16 cm (1.2 to 6.4 in) total 

 length (Levine 1977). 



As blue and channel catfishes mature, larger and 

 more motile prey items (fish and macrocrustaceans) 

 are utilized, but the basic omnivorous habits of the 

 two species are maintained. Adults measuring over 20 

 cm (8 in) feed mostly on macrocrustaceans, fishes, 

 vascular plants, and filamentous algae in brackish wa- 

 ters of Rockefeller Wildlife Refuge (Perry 1969). 

 Principal fishes and macrocrustaceans consumed were 

 bay anchovy, sailfin molly, striped mullet, Gulf 

 menhaden, penaeid shrimps, and blue crab. Studies 

 conducted in Lake Pontchartrain also indicated a 

 greater consumption of fishes and macrocrustaceans 

 by large-sized catfish (DameU 1958). 



In the Atchafalaya Basin, adult blue catfish 

 consumed crayfish, fishes, and vegetable matter 

 (Bryan et al. 1975). Lambou (1961) reported blue 

 crab as the principal food item of adult blue catfish in 

 the Bonnet Carre Spillway near Lake Pontchartrain. 

 Adult channel catfish measuring 15 to 30 cm (6 to 12 

 in) fed on benthic crustaceans, aquatic insects and 

 clams in nearby Lac Des Allemands (Lantz 1970). 

 The increased utilization of larger motile animals does 

 not appear to seriously diminish the importance of 

 other items in the diet of adults of either species. 

 Over 509^. of volume of the food items of Lake Pont- 

 chartrain catfishes consisted of isopods, amphipods, 

 mollusks, and vegetation (Darnell 1958). Hoese 

 (1976) in addition, reported that mollusks (Rangia 

 sp., Congeria sp., and Co rbicu la sp.) were the most 

 common food items recovered from 203 adult 

 blue catfish taken from Atchafalaya and Vermilion 

 bays. 



Literature from outside Louisiana largely sub- 

 stantiates the omnivorous feeding habits of blue and 

 channel catfishes (MUler 1966, Pfiieger 1975). There 

 is little evidence that either species is a selective 

 feeder although they will gather in large numbers at 

 times to feed on certain foods. 



Little information is available on spawning or the 

 early life history of blue or channel catfishes in the 

 Chenier Plain or adjacent coastal waters. The excep- 

 tion is the Atchafalaya Basin, where Bryan et al. 

 (1975) reported that spawning begins in eariy spring 

 and reaches a peak in June and July. A late spring to 

 early summer spawning period is also characteristic 

 of channel catfish in nearby Lac Des Allemands 

 (Lantz 1970). Similar spawning periods are reported 

 for both species from more northern latitudes (Harlan 

 and Speaker 1956, Cross 1967, Pfiieger 1975). 



Under natural conditions, spawning usual- 

 ly takes place in secluded, semi-darkened areas 

 near vegetation, under roots, logs or other debris, or 

 in holes or any bottom depression. Under managed 

 situations both species wUl spawn in man-made 

 shelters (milk cans, wooden boxes, etc.) or on the 

 open bottom in muddy ponds (Miller 1966). Water 

 temperatures at the time of spawning range from 

 15° C to 30° C (59° F to 86° F), with the higher tem- 

 peratures generally being more desirable. Female 

 channel catfish normally spawn only once a year, 

 while males may spawn several times in a season 

 (Clemens and Sneed 1957). 



A well-defined nesting procedure is typically 

 exhibited by both species (Hadan and Speaker 1956, 

 Miller 1966, Cross 1967, Pfiieger 1975). Before 

 spawning, males select and clean out a favorable nest 

 site. Females are then accepted and the externally 

 fertilized eggs are deposited in the bottom of the nest 

 in a large gelatinous mass. Males remain on the nest 

 to protect the eggs from predators and to keep them 

 aerated. Eggs hatch in 5 to 10 days, depending on 

 water temperature, and males guard the fry for a week 

 or so after hatching. Young remain near the nest until 

 their yolk sacs are absorbed, after which they disperse 

 in schools along shallow shorelines. 



Survival of the young has been noted to be 

 greater in turbid than in clear waters (Cross 1967, 

 Lantz 1970, Pfiieger 1975), but it is not certain 

 whether turbid areas are preferred spawning sites. 

 Large schools of young-of-the-year blue and channel 

 catfishes occur along shorelines of the Atchafalaya 

 Basin each fall. It is probable that these habitats serve 

 as nurseries for both species (Bryan et al. 1975). 

 Exact Basin spawning sites are unknown but are be- 

 lieved to be concentrated in rivers, channels, and 

 adjoining lakes. Spawning of channel catfish has been 

 reported to occur in cans or barrels placed in the 

 open turbid waters of Lac Des Allemands (Schafer et 

 al. 1966). 



Although blue and channel catfishes thrive 

 in a wide variety of riverine habitats and coastal bays, 

 their distribution in Louisiana often is governed by 

 changing oxygen, temperature, and salinity patterns 

 (Perry 1967, Lantz 1970, Bryan et al. 1976). 



In coastal waters of the Chenier Plain, salinity is 

 the major controlling factor. Natural spawning of 

 channel catfish has not been reported in salinities 

 exceeding 2%o (Perry 1973), and blue catfish do 

 best in salinities less than 5%o (Norden 1966, Mor- 

 ton 1973, Adkins and Bowman 1976, Hoese 1976, 

 Tarver and Savoie 1976). Intrusion of salt water or 

 blockage of interconnecting coastal waters could be 

 detrimental to both species. 



5.5.3 GIZZARD SHAD (Dorosoma cepedianum), 

 THREADFIN SHAD (Dorsoma peutense), 

 and STRIPED MULLET (Mugil cephalus) 



Although these three species have little or no 

 sport or commercial value, they are valuable forage 

 for predatory fishes, birds, and other animals. Thread- 

 fin shad rarely exceed 20 cm (8 in) in length. Gizzard 



254 



