A COMPARISON OF THE PHYSIOLOGICAL CONDITION OF THE SOUTHERN MULLET LIZA RICHARDSONI (SMITH), IN A CLOSED ESTUARY AND THE SEA

SUMMARY

The physiological condition of the mullet, Liza richardsoni (Smith), from the closed Bot River estuary is compared with that of the same species from False Bay. Levels of protein, lipid, water and ash, as well as energy content were determined in fish from the two environments. Protein (17,94% vs. 18,53 %) and ash levels (3,41 % vs. 4,81 %) were similar in both estuarine and marine fish. Lipid (9,95 % vs. 2,23%) and energy levels (18,35 kJ g-¹ dry weight vs. 14,18 kJ g-¹ dry weight), were significantly higher, while levels of water (67,73% vs. 74,87%) were lower in the estuarine fish. On average the estuarine L. richardsoni were in better condition than their marine conspecifics.

Liza richardsoni does not spawn in estuaries and their better condition in the estuary could possibly be attributed to the retention of energy usually lost through spawning in the sea. On the other hand, estuarine subadults were already in an improved condition, which could only be due to better feeding conditions. It is therefore concluded that estuarine L. richardsoni can maintain a better condition due to both more favourable feeding conditions and the retention of energy usually lost through spawning.