Environmental Biology of Fishes 64: 461–464, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

Book critique

Out of Africa: the success story of tilapias

Christian LevequeProgramme Environnement, Vie et Societes, CNRS, 1 place Aristide Briand, 92195 Meudon Cedex, France

Beveridge M.C.M. & B.J. McAndrew (ed.) 2000. Tilapias: biology and exploitation. Fish and Fisheries Series 25,Kluwer Academic Publishers, Dordrecht. 505 pp. U.S. $ 180.00 (harbound), $ 53.00 (paper)

The tilapiines are originally an exclusive African groupof species. They have since been introduced in differentparts of the world to improve fisheries or to developaquaculture. A huge amount of information is availablefor this group which has received as much attention inthe tropics as the salmonids have in the temperate areas.Actually, tilapias are unusual among tropical fishes inhaving been relatively well served by science.

Tilapia is a common name for a number of cichlidspecies belonging to three main genera: Tilapia,Sarotherodon, and Oreochromis. Apart from their spe-cial interest for fish biologists and taxonomists, tilapiascontribute significantly to African inland water fish-eries and are very good candidates for aquaculture.The identification of these genera, based on breed-ing behaviour, has been a matter of debate amongprominent ichthyologists, including E. Trewavas andD. Thys van den Audenaerde, for a few decades. Recentgenetic studies (Chapter 1) support Trewavas’ viewthat breeding behaviour reflects taxonomy: Tilapia arebiparental – caring substrate spawners, Sarotherodonare biparental and paternal mouth brooders, whileOreochromis are maternal mouth brooders.

Tilapias belong to the family Cichlidae, famousfor the large species flocks of haplochromines in theEast African lakes (Malawi, Tanganyika, Victoria).Compared to fish families that remained unchangedfor millions of years, cichlids are very speciose withno equivalent for adaptive radiation in inland waters(Barlow 2000). There is now evidence that speciesmay have evolved in a few thousand years (or per-haps even less), and several species flocks have beendescribed in different lakes. The existence of suchflocks has also been reported for tilapias, in crater lakesin Cameroon. These observations have contributed sup-port to the hypothesis of sympatric speciation. This

point is not much discussed in this book (Chapter 1),but it has greatly contributed to the change in our think-ing about the mechanisms involved in biological evo-lution. Another issue which is not discussed in thisbook is hybridization, which apparently occurs quitefrequently in the wild, often as a result of a breakdownof geographical isolation between populations, and thebreakdown of reproductive barriers between species.This problem has been exacerbated by the large scaledisplacement of species. Case studies are well docu-mented, such as the disappearance of O. esculentusfrom Lake Victoria after hybridization with the intro-duced O. niloticus, or the successive hybridizations fol-lowing introductions of exotic cichlids in Lake Itashy(Madagascar). The existence of mosaic hybrid zoneshas been documented in Africa, and this may contributeto the high genetic variability observed for severaltilapia species.

The success of tilapias in colonizing a wide range ofhabitats in Africa seems to be due mainly to their foodhabits (herbivory with detritus and invertebrates, so thatfood is rarely a limiting factor), and their flexibilityin growth rate and maturation size according to pre-vailing environmental conditions (Chapter 5). Tilapiasare among the ‘last three species’ (with Clarias andBarbus) which survive when abiotic factors are close orbeyond the tolerance limits for life in aquatic habitats.For instance, the brackish Sarotherodon melanotheronand Tilapia guineensis were the last species recordedduring droughts in the very saline waters (90% seawater salinity) of the Casamance River (Albaret 1987in Leveque 1997).

The success of tilapias in African waters alsoexplains the readiness with which they have spreadin ecosystems outside Africa. O. niloticus andO. mossambicus, for instance, are now widely

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dispersed throughout the tropics where the introductionof fish species in new habitats is presently a matter ofdebate. As a result of the consequences of the introduc-tion of the top predator Lates niloticus in Lake Victoria,and the presumed resulting destruction of the nativehaplochromine species flocks, most scientists are veryreluctant to support new fish introductions. However,for decades, fisheries managers actively introducedfish in many water bodies all around the world withcontrasting results.

Lake Nakuru, for instance, was originally a salinelake devoid of fishes. The successful introduction ofO. alcalicus grahami largely improved the diversityof birds by extending the lake’s food chain to fish-eating birds. The whole ecology of the lake was mod-ified by the introduction of a tilapia but very fewpeople complained because it was, overall, profitableto birds. There are other cases where introduced tilapiahad an impact on native aquatic populations. That isdocumented in warmer southern waters of the U.S.A.(O. mossambicus competition with centrarchids), inAustralia (O. mossambicus devastated indigenous fishpopulation of the Darling River), in Madagascar (wheretilapia eliminated other cichlids) and other places in theworld. In the meantime, fishery biologists documentedmany cases where introduced tilapia species improvedto some extent local fisheries production. One of thebest examples is the Sepik River in Papua New Guineawhere O. mossambicus supported a major fishery with-out known detrimental consequences to the indige-nous fishes (Coates 1987). Obviously, the debate aboutspecies introduction should be more clearly based onboth scientific data and social issues.

Reproductive behaviour in tilapias (Chapter 2) isprofoundly influenced by the breeding systems of thespecies. Mating systems, mate choice, courtship andspawning, habitat use and territoriality, parental care,etc., have been the topics of numerous studies thathave largely improved our knowledge of fish biol-ogy and behaviour. This knowledge also has implica-tions for the exploitation and conservation of tilapias.One peculiar aspect of the reproductive biology oftilapias is the phenomenon of ‘stunting and dwarf-ing’. There are many records of dwarf populations innatural waters, including species like O. macrochir,O. grahami, O. leucostictus, S. galilaeus. This maybe considered as an adaptation towards survival underextreme physical conditions. Stunted populations arecharacterised by a low maximum size and precociousbreeding; they can mature in 3 months compared with2–4 years in other populations. According to Iles,

stunted tilapia may be unique in the cumulative effect ofa combination of changes; marked increase in relativegrowth rate, increase in brood frequency, and decreasein egg size. However, stunting is not unique to tilapiasbut may be regarded as a collective descriptor for avariety of styles, in relation to the remarkable life his-tory plasticity of tilapias which is the legacy of theirevolution in variable habitats. Tilapias may serve asuseful models to explore life history plasticity in fishesin general.

Chapter 4, ‘environmental physiology and energet-ics’, provides an overview of the many experimentalstudies conducted to understand ecological require-ments and the adaptability of tilapiines. They areeuryhaline but not cold tolerant (yet . . . ), so their dis-tribution is restricted to tropical, subtropical or warmtemperate climates. Chapter 4 also raises an importantpoint; conditions and protocols in which experimentsare conducted are frequently widely different betweenlaboratories. Therefore comparisons of data are diffi-cult. This situation is complicated by the substantialvariations that exist within species, so that increasingimportance has to be given to the strain of animals used.

The main part of the book deals with aquacultureof tilapias. Tilapiines increasingly contribute to theworld food supply for humans. Despite the large num-ber of tilapias species, aquaculture has tended to focuson relatively few species, such as O. mossambicus, orO. niloticus. The name ‘aquatic chicken’ has been usedto emphasize the importance of tilapia for aquaculture.Actually, the farming of tilapia has developed rapidlyover the last 20 years, probably reaching 1 milliontonnes nowadays. Much of this increase has come fromthe widespread use of O. niloticus, as well as an increas-ing sophisticated knowledge of food requirements,reproductive physiology, genetics and growth.

Tilapia production can be achieved by two differ-ent ways that can be summarized as low tech versushigh tech culture systems. Low tech, is semi-intensiveproduction in ponds using fertilizers and supplemen-tary feeding. It is claimed to be a means of producinglow-cost fish in developing countries. The advantagesof semi-intensive pond culture are widely recognizedfor simple artisanal production and rural food sup-ply. Tilapias are actually cultured in diverse systemsin inland rural areas, in areas around large cities, inwastewater ponds and even in brackish water pondsin coastal areas. Most semi-intensive pond culture inrural areas is associated with crop and/or livestock pro-duction as part of integrated aquaculture systems, par-ticularly in east and southeast Asia. Pond fertilization

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promotes phosphorus and nitrogen inputs to increaseprimary production and phytoplankton biomass. Live-stock manures are widely used as fertilizers. Semi-intensive and intensive cage culture are also viable in arange of circumstances, from small to large scale andcan contribute usefully to rural livelihoods.

At the same time, entrepreneurs are exploring waysto farm tilapias by high-cost intensive culture usingcomplete feeds, to satisfy rising demand for high qual-ity fish in the developed world. Various species oftilapia, particularly O. niloticus and O. mossambicus,have been reared intensively but such techniques needa high level of expertise and are expensive in capitaland operating cost. In these cases the limiting factoris the price of fish produced and its ability to competewith other products. However, research and develop-ment efforts may contribute to make intensive culturesystems more commercially convincing.

The major concern for aquaculture is to improve theratio of tilapia production to food input. One of theproblems in culture ponds is excessive reproductionand the resulting small size of the fish produced. Mostof the research therefore is focused on methods forthe control of reproduction. Among several techniquesavailable, one is the production of single sex male popu-lations to avoid reproduction during the growing phase.Primitive techniques for hand sexing were not very suc-cessful. The goal of producing all male populations canbe achieved by more sophisticated techniques such ashybridization or the use of hormones. Today, a signif-icant proportion of the tilapia industry is using a syn-thetic androgen in the initial diet for monosex maleproduction. The control of reproduction can also beachieved through chromosome manipulations and pro-duction of triploids. Much of the genetic improvementto date has been through the application of strategiesto improve yield, such as single sex populations orhybridization. For aquaculture purposes the commer-cial advantage of hybridization should be combinedwith selected advantageous traits such as fast growthand increased hardiness and cold resistance, or produc-tion of hybrids with a sex ratio highly skewed towardsmales.

Research programs are also conducted on trans-genic tilapias, but only a restricted number of workshave been published. It does not mean that the topicis without interest, but we have to consider the nega-tive social reaction to genetically modified organisms.The consumer acceptance of transgenic tilapias is a keypoint for the spreading of such techniques, and prob-ably explains the limited information available. The

environmental risk of escaped or deliberately releasedtransgenic fish is hard to predict. However, one canassume that genetically modified fish, if they exist, willbe introduced at some time or another into natural envi-ronments. Ethics are important in the use of geneticallymodified organisms, but scientists usually avoid thistopic.

A lot of effort has also been devoted to the under-standing of nutritional requirements of tilapias. One ofthe chapters devoted to that topic also raises the pointthat ‘caution is advised in the interpretation of the data’,since it has been provided from a number of differentexperimental studies, using varying approaches and indifferent laboratories. ‘Older’ data are most suspect asless was understood about nutrient requirements, inter-actions and the effect of experimental design at thetime that they were derived. It should be rememberedthat tilapia nutrition is still very much an inexact andevolving science. Most importantly, the interpretationof the laboratory derived data in practical tilapia culturesystems needs to be addressed.

In conclusion, I would like to make a few gen-eral comments about some ideas arising from differentchapters of the book. First, it is clear that a lot of aca-demic or research and development work, while veryexpensive, has not always provided reliable data. Formany experimental studies the lack of precise protocols(see Chapters 4 by Ross, and 9 by Jauncey), and some-times the lack of knowledge of the interactions amongbiological factors, result in a huge amount of data whichare quite often of doubtful quality and difficult to applyfor operational purposes. In other words, part of theresearch appears to have been conducted without thenecessary critical approach which characterizes whatis called science, although papers have been evaluatedand published. It is not, of course, a situation peculiarto tilapia. But it raises the question of research eval-uation, and the pressure for publishing more quicklywritten papers based on short term experiments.

A second point, not very clearly expressed in thisbook, concerns the effective contribution of academicresearch to the improvement of tilapia aquaculture pro-duction, compared to farmers’ traditional knowledge.Particularly for semi-intensive pond aquaculture, thefarmers’ experience was probably crucial for the rapidspread of tilapia production in Asia? Did they developinnovative techniques? A major challenge here is thepossible synergy between scientists and fish culturists,how research and expertise are supporting themselves.Can we also assume that the ‘farmers rights’ which arerecognized in agriculture by FAO, also apply to fish

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culture? What about the free access to tilapia geneticresources? I would expect at least a chapter on thistopic, which is a major issue for discussions in theConvention on Biological Diversity.

The third point deals with a paradox. Major aquacul-ture production centres of tilapia are China, Indonesia,Philippines, Taiwan, Thailand, while other candidatesare Columbia, U.S.A., Costa Rica and Venezuela. Inother words, the African tilapia species succeed verywell, as an economic resource, in different parts ofthe world, except Africa where aquaculture produc-tion (apart from Egypt) is still anecdotal. Internationalagencies and bilateral aid have not yet really suc-ceeded in establishing sustainable tilapia aquaculturein Africa, despite several attempts and expensive aqua-culture development schemes. This point is discussedvery briefly in the book (chapter 12 by Young & Muir),while it is in my mind a key question for the devel-opment of the African continent; what are the socialconstraints that could explain the difficulties to adoptaquaculture as an economic perspective?

To conclude, this book provides a good summaryof current academic knowledge on taxonomy, biologyand physiology of tilapia, as well as of prevailing

ideas in the field fish production making use of thetilapia unique biological resource. Most of the chaptersare well documented and clearly written, stressing themajor issues. I clearly understand the difficulties ofsuch an exercise which is to summarize a huge amountof data and expertise. However, I feel slightly unhappyregarding the issues that are presently discussed in theframework of the Convention on Biological Diversity,and not here, such as access to genetic resources, con-servation of species and genetic diversity, fishery man-agement and sustainable development. In other words,the tilapia business should be more open to otherinternational concerns.

References cited

Barlow, G.W. 2000. The cichlid fishes. Nature’s grand experimentin evolution. Perseus Publishing, Cambridge. 335 pp.

Coates, D. 1987. Consideration on fish introductions into theSepik River, Papua New Guinea. Aquacul. Fish. Manage. 10:231–241.

Leveque, C. 1997. Biodiversity dynamics and conservation: thefreshwater fish of tropical Africa. Cambridge University Press,Cambridge. 451 pp.