Ch. 9 — Advances in Reproductive Biology and Their Effects on Animal Improvement • 189 
embryo transfer is strong evidence for the pre- 
dicted use of the technologies, no matter what 
their economic justification. (See app. 11-C.) 
.A major, secondary effect of animal research 
in reproductive biologv' is increased under- 
standing leading to the possible solution of 
human problems— e.g., the concept, efficacy, 
and safety of the original contraceptive pill was 
developed and established in animals. It in- 
volves the same principle as estrous cycle reg- 
ulation discussed above. 
\(U \Cl l,Tl KK 
Aquaculture is the cultivation of freshwater 
and marine species (the latter is often referred 
to as mariculture). W bile fish culture is about 
6,000 years old, scientific understanding of its 
basic principles is far behind that of agriculture. 
.Aquaculture is slowly being transformed into a 
modern multidisciplinary technology, especially 
in the industrialized countries. Increasing 
awareness of human nutritional needs, over- 
fishing of natural commercial fisheries, and ris- 
ing worldwide demand for fish and fish prod- 
ucts are trends that indicate a growth in inter- 
est in aquaculture as a means to meet the food 
needs of the world’s population. 
As part of the trend toward the high tech- 
nology and dense culturing of intensive aqua- 
culture systems in the industrialized countries, 
problems of I'eproductive control, hatchery 
technologv, feeds technologv, disease control, 
and systems engineering are all being investi- 
gated. Reproductive control and genetic selec- 
tion are important because most commercial 
aquaculture operations must now depend on 
wild seedstocks. \'ery little information on the 
animals in culture is av ailable. 
V\ ith all three of the aquaculture genera (fish, 
mollusks, and crustaceans), selective breeding 
programs have long been established, healthy 
gene pools are available, and advantageous hy- 
bridizations have been developed. In fish rais- 
ing, culture systems often demand sterile hy- 
brids, especially of carp and tilapia. Selective 
breeding of salmon has been limited by political 
pressures. V erv little work has been conducted 
with catfish, the largest aquaculture industry in 
the United States. The use of frozen sperm, 
w hich has been successful, should increase be- 
cause of (be sav ings in transport costs. Although 
culture systems for mollusks are fairly well- 
dc'fined, little a|)plied genetics work has been 
done with these po[)ular marine species. Some 
success has been reported in selection for 
growth rate and disease resistance of the 
■ Xmei'ican oyster, and selection for gi’ovvth rate 
of the slow-growing abalone is underway. The 
crustaceans, of w hich the Louisiana crayfish is 
the largest and most viable industry, are the 
least undei’stood. Successful hybrids of lobsters 
bav e been dev eloped. 
Aquaculture suffers from an insufficient re- 
search base on the species of interest. However, 
growing appreciation of and demand for ma- 
rine species should result in increased support 
for basic and developmental work on all aspects 
of control, including basic reproductive biology. 
POULTKY BREEDING 
rhe (|uantitative breeding practices of com- 
mercial breeders have changed very little over 
the last 30 years. Highly heritable traits, such 
as growth I’ate, body conformation, and egg 
weight, ai’e perpetuated by mass selection be- 
cause little advantage is gained from hybrid 
vigor. Low heritable traits (egg production, fer- 
tility, and disease resistance) are perpetuated by 
crossbreeding and identified through progeny 
and family testing. 
The goals of the industry are to increase egg 
production of the layers— both in quality and 
quantity— and, with broilers and turkeys, to im- 
prove growth rate, feed efficiency, and yield, as 
well as to reduce body fat and the incidence of 
defects. 
The technologies of AI and semen preser- 
vation have accelerated the advances made 
through quantitative breeding technology. AI is 
widely used in commercial turkey breeding be- 
cause of the inability of modern strains to mate. 
It makes breeding tests more efficient, steps up 
selection pressure on the male line, reduces the 
number of necessary breeder males, and in- 
creases the number of females that may be 
mated to one male. Semen diluents were intro- 
duced to the turkey industry about 10 years ago 
to lower the cost of AI. Currently, a little over 
