TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

of the fish used in this experiment may not be representative of the general population of
tilapia in the United States.
This research yielded some surprising results, which differentiates the grow-out cycle of
the tilapia from most cold or cool water fishes. First, the optimal growth temperature of
many cool water fish remains relatively constant as the fish grow, but the tilapia
demonstrated a decrease in the optimal growth temperature. Further research is required
to determine if the ultimate growth performance would be obtained by gradually reducing
the temperature as the fish grows. A sudden increase in the food conversion ratio and
slowing of the growth rate in the final five-week period across all the treatments
regardless of size is believed to be associated with the onset of sexual maturity. Most cool
and cold water fish use environmental factors, such as light and temperature as cues to
initiate the spawning cycles. But in tropical fish such as the tilapia, which may not have
these cues in nature, a temporal cycle may initiate sexual maturity.
It should be reiterated that the fish used in this experiment were sex-reversed, graded
twice, and had been selectively bred for several generations. Thus the growth performance
of the fish used in this experiment may not be representative of the general population of
tilapia in the United States.
The onset of maturation in all treatments in the same time interval has reduced a seemingly
complex management problem to a relatively simple management objective. The
overriding objective for the tilapia producer is to grow the tilapia to a marketable size
before the fish matures and the growth rate and feed conversion efficiency dramatically
decline.
The tilapia producer is blessed with an animal that is relatively insensitive to the effects of
temperature, crowding and water quality, and thus has been successful up to this point
inspite of poor management practices. Unfortunately for the recirculating aquaculturist,
the large production benefits anticipated by being able to tightly control the culture
environment are probably unattainable due to the relative insensitivity of performance to
temperature.
The growth and FCR dropped dramatically for all treatments in the final 5 weeks of these
tests, which has important economic implications for the tilapia producer. While the
aquaculturist has always had economic incentive to minimize the production cycle time,
this experiment indicated the extent to which production expenses are rising while
productivity is declining once the fish start to mature. The producer has much incentive to
harvest at an age prior to maturation, within the constraint of the fish reaching marketable
size. The whole price of tilapia is generally a based upon the size, fish greater than 600 g
bring a premium price, those between approximately 350 and 600 an intermediate price,
and those less than 350 g a lesser price (Fitzsimmons and Posadas 1997).
While the specific economic effects will to vary greatly among producers, there are several
management practices that should be adopted to improve profitability. Because the males
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