Anglers and visitors to the underwater world in our beautiful Plettenberg Bay may be familiar with a fish called blacktail Diplodus capensis, though perhaps the name dassie or Cape white seabream is more familiar. This is an oval-shaped fish which is primarily silver in colour with a black patch at the base of the tail. Juvenile blacktail can also have 8-10 thin faint black vertical crossbars on the body, but these are not present in adults. Blacktail are an endemic species, found only from False Bay to southern Mozambique. Surprisingly, Blacktail grow up to 45cm in length, and up to 3kg in weight, though on our local reefs you are more likely to see fish much smaller than this. Blacktail are an abundant, ubiquitous species and juveniles can very often be seen in tidal pools and estuaries and is a popular shore-based recreational and subsistence angling species. Despite their abundance and being classified as Least Concern by IUCN it is illegal to commercially fish, buy or sell this species. Adults, as well as juveniles to a lesser degree, are highly resident, showing high levels of site fidelity to the reefs they call home. At a size of 25 cm which is around 3 years of age blacktail reach sexual maturity. This is a group-spawning species and peaking between September and December both males and females aggregate into a group of eight to fifteen individuals, swim vigorously in a ball near the surface in shallow water, and release sperm and eggs simultaneously into the water column. Fertilised eggs are carried on the currents and are thus distributed along the coastline. An interesting fact about this species is that they are hermaphrodites, where for the first few years of their lives they are male, and at some undefined age and length their gender changes to female.
Written by: Minke Witteveen
For further reading:
- Branch, G.M., Griffiths, C.L., Branch, M.L. and Beckley, L.E. 2010. Two Oceans: A guide to the marine life of southern Africa. Pp. 292. Random House Struik Publishers, Cape Town.
- Mann, B.Q., Buxton, C.D., Russell, B., Pollard, D., Carpenter, K.E. and Sadovy, Y. 2014. Diplodus capensis. The IUCN Red List of Threatened Species 2014. Accessed: 2016-07-16. URL: http://www.iucnredlist.org/details/170175/0.