Observations on Morphological Color Changes in Pontic Shad (Alosa Immaculata, Bennet 1835) during Spawning Migration in the Danube

Abstract

The Pontic shad (Alosa immaculata Bennett 1835) is a Black Sea member of the Clupeidae family that migrates into the Danube via the principal Danube Delta branches and spawns in the upstream reaches of the river. Spawning migration starts as early as February and can last well into the summer, with most commercial capture occurring during peak migration in April-May. The coloration of the fish varies in both color and shade, with clearly distinguishable dark-headed and light-headed individuals depending on the fishing location. Here we draw parallels between shad head coloration and turbidity of the Danube, its delta and Black Sea waters. Further studies focused on morphological color change, as well as targeted fish sampling with corresponding turbidity measurements are needed to test this hypothesis and quantify coloration and color-change mechanisms. Ultimately, head coloration might be a useful indicator of where an individual was captured.

Keywords

• shad
• spawning migration
• turbidity