News
Today, we celebrate the World Fish Migration Day, a global awareness campaign celebrated every two years to highlight the connections that migratory fishes have with human and non-human species, lands, and waters. This day is marked by celebrations, events, and action campaigns organized by people around the world to connect fish, rivers, and people. World Fish Migration Foundation is the main organizer of World Fish Migration Day, and the theme for 2024 is Free Flow.
Migratory fishes are present in many regions of the world. Many fish need to migrate to reproduce, feed and complete their life cycles. The most well-known example is the Atlantic Salmon. They typically hatch in fresh water and live most of the adult life downstream in the ocean, swim back against the stream to the upper reaches of rivers to spawn on the gravel beds of small creeks. As soon as laying is completed, the fish die closing their life cycle. This annual migration is called the salmon run.
Here in Mauritius, we have some fish species which migrate from salt water to fresh water and vice versa. One of them, the Red-tailed Goby (Sicyopterus lagocephalus) – commonly known as ‘cabot’ or ‘bichique’ in Réunion Island and Mauritius - is very folkloric. The bichique can be seen along the coasts of islands in the Indian Ocean as well as in East Africa.
When the fish is at the larval stage, it is subject to intense traditional fishing in Réunion Island while it is also occasionally fished in Mauritius. This tradition was so rooted in Réunion that there is a maloya song.
You would have heard the lyrics which says, “bichique la monte”. As this particular phrase suggests, the species literally migrates from the sea to rivers in large groups. The female lays its eggs in fresh water. After hatching, the larvae repeatedly rise towards the surface of the stream and then sink down again; this helps them to get carried along by the current. On arrival in the marine environment, they are between 1 and 4 mm and start to feed on plankton. They are translucent at this stage and remain at sea for less than around 250 days before feeling the urge to migrate back into fresh water.
The post-larval stage starts as they re-enter the estuaries. They have already developed suction discs, but now they undergo metamorphosis, their mouths move from the tip of the snout to the underneath of the head, they begin to develop pigment, the pectoral fins transform, the tail loses its fork, they grow teeth on the premaxillae bone, changes occur in the cranium and changes in osmoregulation take place. As the rake-like teeth push through, they start to feed on diatoms and algae that they scrape off the substrate. After two days in the estuary, the juvenile fish move upstream, overcoming small waterfalls with the aid of their suction discs, and after about three or four weeks of migration start to take up territories in the fast-flowing streams where they will breed. The circular movement described above starts all over again, in a movement that has span thousands or millions of years. This age old movement is regrettably affected by damming and deviation of rivers, water extraction, agricultural chemicals and invasive aquatic species.
