This whole strategy is devoted to protecting the developing 
eggs for perhaps two reasons. A female can produce only a 
limited number of eggs because of her small size (adults are 
about 50-70 mm total length.) Fish from the Ottawa District 
that I have examined contain as few as 120 eggs, although there 
may be several hundred produced in a season. This situation 
compares dramatically with species that broadcast their eggs and 
leave them to chance survival. (The large carp may deposit over 
two million eggs, and even small species such as Silvery Minnows 
can produce up to 6,600 eggs.) Survival of fathead eggs cannot 
be left to chance, and some kind of care and defense is an 
evolutionary advantage. The second reason is that the favoured 
environment of fatheads often has a mud bottom. The inverted 
position of the nest protects the eggs from being smothered and 
also conceals them from some predators. 
The function of the pad brings in another fascinating 
aspect of fathead biology. The pad secretes a mucus which is 
used to clean vigorously the spawning surface and to protect the 
developing eggs. This rubbing, and possibly the chivvying and 
lifting of females, should present a problem to fatheads. Like 
other minnows, they have the remarkable capacity of releasing an 
alarm substance into the water if the skin is abraded. Other 
fatheads detect this chemical and go into a fright reaction 
which may save them from predators. 
A male fathead could not go through a successful courtship 
if it kept releasing alarm substance whenever it cleaned the 
spawning site or rubbed against a female. The male would 
frighten itself and potential mates away from the spawning site. 
In fact, male fatheads lose the ability to produce alarm sub¬ 
stance during the breeding season. This is not a disadvantage 
to the males since the substance works only to protect other 
fatheads when they are within scenting distance of each other. 
If a male retained the alarm substance and was eaten by a preda¬ 
tor during the breeding season, the alarm would not be passed 
along because breeding males keep their territory clear of other 
fatheads except for the brief courtship and egg laying by fe¬ 
males. The males do retain their own fright reaction to alarm 
subtance from other fatheads. Females do not lose their alarm 
substance, suggesting there is little abrasion during courtship 
and it is the cleaning function of the pad in preparing the nest 
site that necessitates a temporary male loss of alarm substance. 
Of course, fighting males could cause abrasion and release alarm 
substance. The male defending a nest site needs his wits about 
him and does not want to set off a panic reaction in himself. 
However, the butting of males seems to be of a tubercle to 
tubercle type, and little injury results. 
And finally, fatheads are so named not because of any 
mental deficiency, but because males have short, rounded and, 
hence, fat heads, n 
86 
