The Biology and Culture of Tilapias

tion potential, at low input cost. In intensive systems, both S. aureus and S.
niloticus provide high production. It may be concluded that these tilapias
have good production potentials, particularly in culture systems with low-
energy inputs, where production costs may be kept relatively low. Even
then, the average monthly production is above that experienced for super-
intensive pond culture in Israel: estimated at about 0.5 kg/m3/month, i.e.,
about 60 t/ha/year (Sarig and Arieli 1980).

2. COMPARISON WITH OTHER CULTURED SPECIES

The production potential of the S. aureus and S. niloticus in intensive
systems is compared with that for Cyprinus carpio, Ictalurus punctatus and
Salmo gairdneri in Table 18 (Coche 1978, 1979). The two tilapias can
outperform I. punctatus and Salmo gairdneri, especially considering both the
relative ease of tilapia culture and its efficient use of low-cost feed. C. carpio
grows faster and has a definitely higher production potential, although this
alone might not justify its preference as a cultured species over S. aureus
or S. niloticus.

Discussion

MORIARTY: How much of a problem is there with fouling of the cages by filamentous
algae and other organisms growing on the walls of the cages and restricting the water
flowing through them?

COCHE: It depends on the environment where you are keeping your cages. In very rich
environments, you can have problems, but in general tilapias help to clean the cages.

PULLIN: In the Philippines, tilapia actually eat the filamentous algae growing on the
sides of the cages, so much so that it may be an important source of extra food for
them.

COCHE: It can also be a problem for the cage netting. During this process, we have had
tilapia damaging some of the netting.

NASH: Just a comment. I do not altogether accept your interpretation that as the cage

size increases, the production tends to go down. I think that it does in regular, either

hexagonal, square, or circular cages, but certainly in the early days of marine cage devel-

opment in Scotland we found that the elongated cage opened up new dimensions of

production for you, although structurally it was easier to make the square, hexagonal, or

circular cage. Secondly, we cut down a great deal on food loss by having about two-thirds

of the bottom being covered with some sort of plate which stopped the food going right

through. The only problem was then that as we moved many of these cages up and down

in the water, particularly if they were submerged cages, the phugoid motion often put the

cages under tremendous stress and in fact cracked several of them. But certainly, if you

have floating cages, I think that plates up to about 213 of the bottom structure are a help

to reduce food loss.

HEPHER: Dr. Nash, could you explain the superiority of the elongated cage over the

round one with respect to yield and production?

NASH: I think one is just more limited with a round or regular cage because it is largely

the movement of the fish within the cage that maintains good circulation. With a regular