In the Tinja channel, which links the Bizerte lagoon to Lake Ichkeul, salinity can rise above that of the sea during droughts. Yet a small fish known for its tolerance of salt is missing precisely where the water is less salty.
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This is Aphanius fasciatus, a small cyprinodontid of Mediterranean transitional waters. It copes with strong salinity swings, but its presence in lightly salty water remains limited. In a laboratory experiment on early life stages, eggs died more often and young fish survived less well in low-salinity water than in saltier water.
To explain its absence, part of the scientific literature points mainly to competition from the invasive fish Gambusia holbrooki, rather than to salt itself. This interpretation is still debated, so salt may not be the only culprit.
Tunisian lagoons also show marked swings. Over a monitoring period of about five years, the monthly average salinity of the Tinja channel ranged from 7.9 to 46.3 ‰. During the most severe droughts, freshwater-associated species disappear.
