Fish mortalities on Touw Estuary

South African National Parks is monitoring the Touw River estuary closely following the death of fish that amounted to 159 since the 20th August 2019.

 Jonathan Britton, Marine ranger in Wilderness says ‘the first mortalities were noticed in mid-August and have been restricted to the lower section of the Touw Estuary. The mortality event appears to be short lived, as mortality numbers have dropped off significantly since 20 August.

SANParks rangers intervened by regular patrols in the area to identify species impacted, count total mortalities and remove carcasses.

In addition to water quality being checked sick fish were caught, euthanized and various blood and tissue samples taken by SANParks Scientific Services in Rondevlei,  Departmental colleagues from Cape Town and an independent scientist from George to determine the type of infection.

Underwater cameras were also deployed to visually observe the fish. At this stage superficial examination indicates the presence of both a bacterial and fungal infection. 

Fortunately the infections do not appear to be flesh eating. ‘Bacterial and fungal infections in fish are not well documented and this is also an opportunity to increase our understanding of these processes’ says Britton.

Although the cause of the infection is not known at this stage, all water quality monitoring conducted till this point indicates nothing off particular concern.

The water quality results are well within parameters that would be expected during the closed phase of the Touw River Estuary and do not exceed any thresholds that would be detrimental to estuarine fish species. There is also no indication of any sewage or pollution spill.

SANParks will continue to monitor the situation and will provide updates as they become available.

On a positive note during the week it was also observed that there appeared to be a healthy population of juvenile estuarine fish that did not show signs of fungal or bacterial lesions.

SANParks recommends that until further knowledge is gained precaution is taken and people refrain from eating fish that have abnormal looking lesions on their skin and avoid collecting dead fish for consumption in the Touw Estuary.

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