) 



STAGES IN THE DEVELOPMENT OF 

 ICTALURUS NEBULOSUS 



Ictalurus nebulosus, the brown bullhead or 

 horned pout, is generally distributed through- 

 out the Eastern and Central United States from 

 Maine and the Dakotas on the north into the 

 Gulf States on the south. It has been introduced 

 successfully into streams and ponds on the West 

 Coast and into the waters of several European 

 and Far Eastern countries. 



Under favorable conditions adult bullheads 

 attain a length of a foot or more with occasional 

 specimens 18 inches in length weighing 3 to 4 

 pounds. When crowded they are much smaller. 

 Ictalurus nebulosus is very tenacious of life, 

 surviving under conditions which will not sup- 

 port other native fishes. It is commonly found 

 in small ponds, lakes, and sluggish streams and 

 does well even in a muddy habitat. The adults 



| are frequently caught on a drop-line during the 

 daytime but are more active at night. The eyes 

 are small but the olfactory and cutaneous senses 

 are highly developed. They are omnivorous, 

 the diet depending on what is available. The 

 adults are readily collected in a baited minnow 

 trap with an adequate entrance and with reason- 

 ble care will survive well in aquaria. 



The reproductive habits of Ictalurus nebu- 

 losus have been observed in both natural sur- 

 roundings and in aquaria. The eggs are usually 

 deposited in a prepared nest, an open shallow 

 excavation among weeds, or a burrow excavated 

 by the adults under the roots of a water plant 

 which will support the roof of the nest. A com- 

 mon site for such a burrowed nest is horizontally 

 for as much as three feet into the bank of the 

 stream or pond. The bullhead resembles the 

 wren in selecting a nesting site, taking advantage 

 of protected locations in pails, stovepipes, rub- 

 ber tires, cinder blocks— or under boards, stones, 



| or other articles thrown by chance into the 



water. Rarely are the eggs laid in an open site 

 without preparation. Depending on the nature 

 of the nest, the floor is invariably some firm 

 material— coarse sand, gravel, or stone. When 

 the nest is found in the muddy bottom of a 

 pond, it is located where the mud is a shallow 

 layer on a sandy or gravel bottom to which the 

 nest is excavated. Drainage tiles provide attrac- 

 tive nesting sites for bullheads. Tiles are par- 

 ticularly useful in ponds supporting a heavy 

 growth of weeds in which it is difficult to locate 

 the natural nesting sites. The tiles should be 

 distributed separately around the margin of the 

 pond in two or three feet of water, their loca- 

 tions indicated by a suitable marker. 



The eggs are adhesive when laid and form a 

 spongy pale yellow mass which adheres to the 

 floor of the nest. Each egg through its chorionic 

 membrane has adhesion discs with several adja- 

 cent membranes which sometimes show up on 

 the surface of the chorionic membranes when 

 they are torn from each other (see figure of 

 Stage 20) . The micropyle is located as the center 

 of a stellate structure seen in some membranes 

 (Stage 1 et al.). When the eggs are laid in indi- 

 vidual drainage tiles it is frequently necessary 

 to gently scrape the egg mass free of the tile to 

 which it adheres. If the floor of the nest is sand 

 or gravel, grains of sand and small pebbles are 

 found adhering to the egg mass. There are from 

 several hundred up to a thousand and more eggs 

 in a single egg mass. The adults, particularly 

 the male, guard the eggs. Frequently an ob- 

 server can flush the adult off a nest by wading 

 in a pond a few yards off shore, locating as close- 

 ly as possible the point at the bank from which 

 the adult emerges. Close inspection of the bank 

 at this point will usually reveal the opening of 

 the nest. The collector can reach into the bur- 



