The Biology and Culture of Tilapias

General Discussion on the Biology and Culture of Tilapias

Compiled by R.S.V. Pullin

Abstract

A report is given on a wide ranging discussion on the biology and culture

of tilapias. The topics covered include speciation, species for aquaculture,

establishment and conservation of pure strains, the concepts of stunting and a

switch between somatic growth and gametogenesis/spawning, the physiology

of digestion in tilapias, detritus and detritivory, feed formulation, food

presentation, broodstock nutrition, broodstock management, mass seed

production, recruitment control, integrated farming and wastewater reuse,

and diseases of tilapias.

Classification and Speciation

Dr. Trewavas began by outlining the classification and interrelationships
of the tilapias. It is generally accepted that the mouthbrooding species arose
from ancestral substrate-spawning Tilapia and from a narrow group of these.
Prof. Peters thinks that this may have happened several times, including the
comparatively recent evolution of the species of the Cameroon crater-lake,
Barombi Mbo. For this reason he thinks it inappropriate to unite those of
more ancient origin with the more recent ones in one genus separate from
Tilapia. He would retain the generic name Tilapia for all of them. But the
mouthbrooders are alike, not only in their reproductive arrangements but
also in their feeding habits and structures, and the Sarotherodons in Barombi
Mbo are in Dr. Trewavas' opinion derived from species that were already
mouthbrooders and microphagous feeders. This is not to say that there are
no mouthbrooders derived independently from Tilapia, but these have not
developed the same feeding structures as Sarotherodon.
There is more than one way of expressing such opinions in the nomen-
clature, and it is proposed to adopt the name Sarotherodon for all the
mouthbrooding tilapias (but see Preface and Addendum, p. 11-12). There is
no doubt that the east and central mouthbrooding species belong to a branch
or branches that have long been separated from the west African. This may
be expressed by regarding them as separate subgenera, a rank that may be
disregarded by those not specialists in taxonomy.
Methods of speciation were discussed and the main point emerging was
that speciation among the tilapias has been almo& exclusively by spe-
cialization following geographical separation, i.e., allopatric. Among the
notable exceptions where sympatric speciation is thought to have occurred,
that in Lake Barombi Mbo is the most interesting. This 2.5 km diameter
lake has 11 species of endemic cichlids, including four which are arguably
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