Tigers without teeth

Tigerfish are well equipped for their predatory lifestyle with an impressive set of sharp, prominent teeth

Tigerfish have a fearsome reputation as predators and fighting game fish. Their scientific name Hydrocynus vittatus means ‘striped water dog’ in reference to their dark lateral stripes and impressive set of sharp teeth.  Yet tigerfish are not always quite so fiercely endowed.  Daniel Nel, a guide at Chongwe River Lodge recently reported catching a number of specimens that appeared to be losing or have lost their teeth and wondered whether this is cause for concern.

Tigerfish are part of the family Characidae are large group of freshwater fishes found across Africa and the Neotropics. Tooth loss is not uncommon in the characins and tigerfish are no exception. There have been several accounts of anglers catching toothless tigerfish from the Zambezi and other areas and it does not necessarily indicate a problem with the fish themselves. In Lake Kariba, a toothless tagged tigerfish was caught and then recaptured several months later, still toothless. However, the incidence of anglers catching tigerfish during tooth replacement is usually quite low. So, while tooth replacement is a natural phenomenon in tigerfish, it is not often observed by anglers and it is certainly unusual that ten fish exhibiting tooth replacement were caught at Chongwe within the space of a month.

Field and laboratory observations on tigerfish from the Kruger National  Park in South Africa suggest that tooth replacement occurs several times during the development and growth of tigerfish and they will lose and replace teeth several times during the first two  years of development but tooth replacement does not seem to be restricted to any particular age. The toothless tigerfish caught this year at Chongwe ranged from between two and eleven pounds. The Kruger Park  study also found that tooth replacement occurs quite rapidly, taking only three to five days to completely replace a set of teeth. Initially the teeth will become loose, pointing in different directions and the gums and mouth will appear swollen. The teeth fall out in no particularly order and are quickly replaced by new teeth, which appear small at first but grow rapidly. During this time, the fish may be reluctant to feed, but will return to normal feeding behaviour once the teeth are fully grown.  Teeth are an integral part of the ability of tigerfish to hunt and catch prey. It is difficult to imagine a tigerfish hunting successfully without teeth, which is probably why relatively few toothless tigerfish are caught  by anglers. Although tigerfish can replace teeth throughout the year, tooth replacement may occur with higher frequency during spring or summer, which combined with increased fishing effort during the peak of the recreational fishing season, could explain the phenomenon being  observed with an unusually high frequency at Chongwe.

 

This is a good example of why monitoring and record keeping are so important. Firstly, unusual phenomena can be detected and reported, which would be vital in the case of a disease outbreak or other environmental problem. Secondly, good baseline data on the status and health populations and more people taking an interest in the fish that they catch provide observations that can lead to directions for further research or conservation action.

If you do happen to catch a toothless tigerfish, this does not necessarily indicate that anything is wrong with the fish, so you should still follow the usual release procedures.  If released properly, that fish should be back to its usual fearsome self in a few days. Nonetheless, if you do observe anything unusual about the fish that you catch, make a note or take a photograph and report it to CLZ or to the LZCRI here so that we can tell you more about it and remain aware of any potential conservation issues.

References:
Begg GW. 1973. Some abnormalities and an interesting anatomical feature occurring in the tigerfish Hydrocynus vittatus at Lake Kariba. Piscator 86: 110-112.
Gagiano CL, Steyn GJ & du Preez HH. 1996, Tooth replacement of tigerfish Hydrocynus vittatus from the Kruger National Park. Koedoe 39(1): 117-122 (Full text here)
Gaigher  IG. 1975. Evidence for tooth replacement in the tigerfish Hydrocynus vittatus. Arnoldia 7(10): 1-4.
Kenmuir DH. 1973. The ecology of the tigerfish Hydrocynus vittatus Castelnau, in Lake Kariba. Occasional Papers of the National Museums and Monuments of Rhodesia. B5(93): 115-170.
Tweddle D. 1982. Tooth replacement in the tiger-fish Hydrocynus vittatus Castelnau.  Journal of Science and Technology (Malawi) 3(1): 33-35.

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