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Causes of mortality in the endemic Tilapia of Lake Chilwa (Malawi)

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Summary

During 1966 and 1967 extensive mortalities of Tilapia shirana chilwae took place in Lake Chilwa, Malawi. By collating field observations and physico-chemical data from the lake with experimental evidence from the laboratory, it has been possible to predict what the most likely causes of mortality of Tilapia might have been.

High winds caused bottom erosion in October 1966, and the released mud deoxygenated the water. Total deoxygenation of the water results if the level of suspended matter is raised to 12,860 ppm. Tilapia are able to survive levels of oxygen as low as 0.6 mg/l, but become distressed below this figure.

The median lethal alkalinity for T. s. chilwae in artificial lake water is 61.6 meq/l. This concentration was reached in the lake in December 1966, and probably caused further mortalities.

T. s. chilwae is remarkably tolerant of high temperature, and this factor alone is unlikely to have caused natural mortalities. Elevated temperatures can cause decreased resistance to low oxygen and high ionic concentrations, however, and the dense blooms of Anaebena may have caused sufficient deoxygenation of the water at night to cause further mortalities.

T. s. chilwae is more resistant to high alkalinity and high temperature than T. melanopleura. This undoubtedly reflects the long history of stress in the endemic Tilapia. No doubt the heightened resistance of T. s. chilwae has enabled it to successfully populate L. Chilwa, despite its characteristic instability.

Zusammenfassung

Betrachtliche Mortalitäten des Fisches Tilapia shirana chilwae erfolgte im Chilwa See (Malawi) in 1966 und 1967. Bei der Zusammenfügung von den Beobachtungen am See und den physischchemischen Daten des Sees mit experimentellen Daten aus dem Laboratorium, war es moglich die wahrscheinlichen Ursachen des Mortalitäts festzustellen.

Starke Winde verursachten die Erosion des Bodens im Oktober 1966 und der aufgelöste Schlamm entfernte die Sauerstoffe des Wassers. Totale Entfernung des Sauerstoffes folgte als tas Niveau des aufgelösten Materials einen Wert von 12,800 t.p.m. erreichte. Obgleich Tilapia einen so niedrigen Sauerstoffniveau von 0.6 mg/l überleben können fühlen she sich unheimlich unter diesem Wert.

Die mediane letale Alkalinitat für T. s. chilwae im künstlichen Seewasser ist 61.6 meq/l. Diese Konzentration wurde im Dezember 1966 im See erreicht und verursachte wahrscheinlich eine weitere Mortalität.

T. s. chilwae ist auffällig tolerant hohen Temperaturen gegen-über und es ist unwahrscheinlich dasz these Tatsache allein natürliche Mortalitäten verursacht hat. Dennoch können erhdhte Temperaturen eine abnehmende Resistenz gegen niedrigen Sauerstoff und hohe Ionen-Konzentration verursachen und die dicke Bliite von Anaebena könnte eine genügende Desoxygenation des Wassers in der Nacht veranlasst haben um weitere Mortalitaten zu verursachen.

T. s. chilwae zeigt stärkere Resistenz gegenüber hoher Alkalinität und hoher Temperaturen als T. melanopleura. Dieses reflektiert, ohne Zweifel die lange Geschichte von Stress in die endemische Tilapia. Die erhöhte Resistenz des T. s. chilwae, dasz es für these Fische möglich war den Chilwa See zu bevölkern, trotz ihrer charakteristischen Instabilität.

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References

  • Allanson, B. R. & Noble, R. G. - 1964 - The tolerance of Tilapia mossambica (Peters) to high temperature. Trans. Amer. Fish Soc., 93, 4: 323–332.

    Article  Google Scholar 

  • Beadle, L. C. - 1969 - Osmotic regulation and the adaptation of freshwater animals to inland saline waters. Verb. Internat. Verein. Limnol. 17: 421–429.

    Google Scholar 

  • Bowmaker, A. P. - 1965 - The fisheries of Zambia, Mweru-wa-Ntipa. Natural Resources Handbook, Ministry of Lands and Natural Resources, Zambia. 58–60.

    Google Scholar 

  • Brown, M. E. - 1957 - The physiology of fishes. Vol. 1. Academic Press Inc., New York.

    Google Scholar 

  • Chervinski, J. - 1961 - Study of the growth of Tilapia galilaea (Artedi) in various saline concentrations. Bamidgeh, 13, 3/4: 71–74.

    Google Scholar 

  • Chipeta, W. - 1968 - Cyclical and secular changes in Lake Chilwa water level and its fisheries. Cyclostyled report No. 1. University of Malawi.

  • Coe, M. J. - 1966 - The biology of Tilapia grahami in Lake Magadi, Kenya. Acta Tropica, 23: 146–177.

    Google Scholar 

  • Conte, F. P. - 1969 - Salt secretion, in Fish physiology, Vol. 1. Eds. Hoar, W. S. & Randall, D. J. Academic Press, London.

    Google Scholar 

  • Dharmamba, M. & Nishioka, R. S. - 1968 - Responses of “prolactin-secreting” cells of Tilapia mossambica to environmental salinity. Gen. Comp. Endocrinol. 10, 3: 409–420.

    Article  Google Scholar 

  • Erichsen Jones, J. R. - 1964 - Fish and river pollution. Butterworth & Co. Ltd., London.

    Google Scholar 

  • Evans, R. C., Purdie, F. C. & Hickman, C. P. - 1962 - The effect of temperature and photoperiod on the respiratory metabolism of rainbow trout, Salmo gairdneri. Can. J. Zool., 40: 107–118.

    Article  CAS  Google Scholar 

  • Farmer, G. J. & Beamish, F. W. H. - 1969 - Oxygen consumption of Tilapia nilotica in relation to swimming speed and salinity. J. Fish, Res. Bd. Canada 26: 2807–2821.

    Article  CAS  Google Scholar 

  • Fish, G. R. - 1955 - Some aspects of the respiration of six species of fish from Uganda. J. Exp. Biol. 33, 1: 186–195.

    Google Scholar 

  • Herbert, D. W. M. & Merkins, J. C. - 1961 - The effect of suspended mineral solids on the survival of trout. Int. J. Air Wat. Poll. 5, 1: 46–55.

    CAS  Google Scholar 

  • Hickling, C. F. - 1961 - Tropical inland fisheries. Longmans. London.

    Google Scholar 

  • Hoar, W. S. & Randall, D. J. - 1969 - Fish Physiology. Vol. 1. Academic Press, London.

    Google Scholar 

  • Houston, A. H., Reaves, R. S., Madden, J. A. & De Wilde, M. A. - 1968 - Environmental temperature and the body fluid system of the freshwater teleost — 1. Ionic regulation in thermally acclimated rainbow trout, Salmo gairdneri. Comp. Biochem. Physiol. 25: 563–581.

    Article  CAS  PubMed  Google Scholar 

  • Hutchinson, G. E. - 1936 - Alkali deficiency and fish mortality. Science 84: 18.

    Article  CAS  PubMed  Google Scholar 

  • Jubb, R. A. - 1967 - The freshwater fishes of Southern Africa. Balkema, Capetown/Amsterdam.

    Google Scholar 

  • Kirk, R. G. - 1967a - The fishes of Lake Chilwa. Soc. Malawi J. 20: 35–48.

    Google Scholar 

  • Kirk, R. G. - 1967b - Cyclostyled Report, Department of Fisheries, Malawi.

    Google Scholar 

  • Kirk, R. G. - 1970 - A study of Tilapia shirana chilwae Trewavas in Lake Chilwa, Malawi. Ph.D. Thesis, University of London.

  • Lotan, R. - 1960 - Adaptability of Tilapia nilotica to various saline concentrations. Bamidgeh, 12, 4: 96–100.

    Google Scholar 

  • Mackay, W. C. & Beatty, D. D. - 1968 - The effect of temperature on renal functions in the white sucker fish, Catostomus commersonii. Comp. Physiol. Biochem. 26: 235–245.

    Article  Google Scholar 

  • Mackereth, F. J. H. - 1963 - Some methods of water analysis for limnologists. Sci. Publ. Fresh. Biol. Ass. 21: 1–71.

    Google Scholar 

  • McLachlan, A. J. & McLachlan, S. M. - 1969 - The bottom fauna and sediments in a drying phase of a saline African Lake (L. Chilwa, Malawi). Hydrobiologia, 34: 401–413.

    Article  CAS  Google Scholar 

  • Moore, W. G. - 1942 - Field studies of the oxygen requirements of certain freshwater fishes. Ecology, 23: 319–329.

    Article  CAS  Google Scholar 

  • Morgan, A. - 1968 - A physico-chemical study of Lake Chilwa. M. Sc. Thesis. University of Malawi.

  • Morgan, A. & Kalk, M. - 1970 - Seasonal changes in the waters of Lake Chilwa (Malawi) in a drying phase, 1966–68. Hydrobiologia, 36: 81–103.

    Article  Google Scholar 

  • Mortimer, M. A. E. - 1962 - Notes on the salinity tolerances of certain Tilapia species (Cichlidae: Pisces) in Northern Rhodesia. J.F.R.O. Ann. Rep. 9: 63–64.

    Google Scholar 

  • Moss, B. & Moss, J. - 1969 - Aspects of the limnology of an endorheic African lake (L. Chilwa, Malawi). Ecology, 50 (1): 109–118.

    Article  CAS  Google Scholar 

  • Mzumara, A. J. P. - 1967a - The Lake Chilwa fisheries. Soc. Malawi. J. 20: 58–68.

    Google Scholar 

  • Mzumara, A. J. P. - 1967b - Cyclostyled report, Department of Fisheries, Malawi Government.

  • Olsen, T. A. - 1932 - Some observations on the interrelationships of sunlight, aquatic plant life and fishes. Trans. Amer. Fish Soc. 62: 278–289.

    Article  Google Scholar 

  • Potts, W. T. W., Foster, M. A., Rudy, P. P., & Parry Howells, G. - 1967 - Sodium and water balance in the Cichlid Teleost Tilapia mossambica. J. Exp. Biol. 47: 461–470.

    Google Scholar 

  • Rensen, H. L. F. - 1969 - Fish Marketing. Report of Ministry of Agriculture Malawi Government.

  • Shilo, M. - 1951 - Toxic blue-green algae in fish ponds in Israel. Bomidgeh, 3: 146–153.

    Google Scholar 

  • Tait, C. - 1965 - Mass fish mortalities. Fisheries Res. Bull. Dept. Game and Fisheries, Zambia. 3: 28–30.

    Google Scholar 

  • Talling, J. F. & Talling, I. B. - 1965 - Chemical composition of African lake waters. Int. Revue ges. Hydrobiol. 50: 421–463.

    Article  Google Scholar 

  • Thompson, D. H. - 1925 - Some observations on the oxygen requirements of fish in the Illinois River. Bull. Ill. Lab. Nat. Hist. 15: 423–437.

    Google Scholar 

Download references

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  1. Peter R. Morgan
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University of Malawi

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Morgan, P.R. Causes of mortality in the endemic Tilapia of Lake Chilwa (Malawi). Hydrobiologia 40, 101–119 (1972). https://doi.org/10.1007/BF00123596

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