flagtail prochilodus 17 cm

Semaprochilodus are one of the most common and widespread shoaling fish found in South America. Over a dozen species have been described but most are never imported. They are used as food fish in their nativecountries. It makes a stunning addition to a community of larger fish.

Along with some congeners, S. insignis is commonly known as the Jaraqui in Brazil. It is an interestingspecies both ecologically and biologically. In nature it migrates over large distances in huge shoals according to the season, feeding on organic detritus. This detritivorous feeding habit and migratory nature plays an important part in maintaining ecosystem structure and dynamics as it processes large amounts of organicsediments as it sifts for food. It also has two stomachs, one of which is filled with mud to aid digestion.

It migrates twice a year. The first event is a spawning migration at the start of the wet season, when the fish move from nutrient-poor black and clear water tributaries and streams into the more turbulent white (silt-laden) waters near the heads of rivers to spawn. They may travel several hundred kilometres and can even be seen leaping through rapids in a similar fashion to salmon. Post-spawning the fertilised eggs drift downstream and into the nutrient rich floodplains. These act as the perfect “nurseries” for the fry to feed and grow.

The adults meanwhile return to exactly the same flooded forest tributary from where they came to feed for the next 3-4 months. They then migrate again in the middle of the wet season, moving once more from the tributaries upstream into the nutrient-rich rivers, where they may enter many different tributaries. They continue this activity until the water level drops. When it rises once more the fish spawn again in the mouth of the tributary they are currently in.

Interestingly it appears that older fish do not undertake these migrations, as reported by Ribeiro and Petrere (1990). They did not suggest an age limit for migration but did note that non-migratory fish were much larger than the migrating individuals and tend to occur further up the tributaries.

It can be distinguished from the other commonly-imported species, S. taeniurus by the fact that the dark spots present on the flanks of juvenile specimens fade as the fish matures. In S. taeniurus these remain throughout the fishes’ life.