Assessing the food habits of Crassostrea tulipa (L. 1819) in a commercial fishery of a Ramsar site in Ghana

Abstract

The development of wild commercial oyster culture in Ghana is of recent concern. Reduction in feed cost through reliance on natural feed sources is an important sustainable aquaculture management strategy. In many parts of sub-Saharan African countries including Ghana, there is limited documented information on the natural food items fed on by Crassostrea tulipa (Lamarck, 1819). The oyster in the Densu estuary was studied for food habits using the Numerical, Frequency of Occurrence, and Index of Relative Importance (IRI) methods and condition index for a duration of 18 months. The diet of the oyster was dominated by golden algae (Phylum Ochrophyta; IRI=595), red algae (Phylum Rhodophyta; IRI=209), green algae (Phylum Chlorophyta; IRI=131.37) and diatoms (Phylum Bacillariophyta; IRI =172). There was a high species diversity (D = 6.60 ± 0.10 - 7.01 ± 0.03; H '= 0.30 ± 0.12 - 0.32 ± 0.05) among the food items ingested by C. tulipa. Golden algae was the most abundant (IRI= 56%), followed by red algae (IRI = 16%) and the diatoms (IRI = 13%). The less abundant phyla were Chlorophyta (IRI= 8 %), Cynophyta (IRI = 6 %) and Arthropoda (IRI = 1 %). The oyster was in a good state of wellbeing (Mean Condition index = 139.50 ± 0.11) and feeds on a wide range of plankton species. This information is essential in the development of natural feed for the oyster industry in Densu estuary. The presence of green algae in the diet requires further investigation to help minimize the possible toxic effects it may have on the fishery and humans.