Food and Feeding Habits of Parailia Pellucida (Boulenger, 1901) (Schilbeidae) in the Freshwater Reaches of the Nun River of the Niger Delta, Nigeria

Abstract

The Food and Feeding habit of the glass schilbid Parailia pellucida was investigated with 654 stomachs using the numerical, frequency of occurrence and points methods such that 368 (56%) were empty while 286 (44%) contained food items. In the numerical method the number of different food items were counted and recorded. For the frequency of occurrence method, all stomachs containing particular food items were recorded while in the points method; points or marks were allocated to the food items based on their relative volumes in the stomachs. The degree of fullness was estimated by an arbitrary 80 points scale allotted as follows: empty stomach (o); trace (10); quarter-full (20); half-full (40); three-quarter full (60) and fully distended stomachs, 80 points. Observed food items were cladocera, copepoda, insecta, nematoda, ostracoda, rotifera, algae, fish remains/eggs, sand and unidentified organisms. By the numerical composition, cladocerans were predominant, (63.8%) algae (24.96%), rotifera (4.67%), copepoda (4.5%) and insecta (1.74%). By the frequency of occurrence method, cladocera was dominant in (39.8%), algae (21.8%), while insects, copepods and rotifers constituted 13.6%, 10.4% and 9.5% respectively. In the points method, Cladocerans scored the highest (81.6%), copepods (6.3%) while insects, rotifers and algae scored 4.22%, 3.86% and 3.18% respectively. The primary food items of P. pellucida with the index of food significance (IFS) ≥ 3% include cladocerans such as diaphanosoma (35.4%), bosmina (34.95%), pseudosida spp (17.71%) and copepod cyclop spp (5%). The major secondary food items (IFS ≥ 0.1 to < 3%) were brachionus (rotifer) (2.35%), monoraphidium (algae) (1.91%) and bosminopsis (cladoceran) of 1.56%. The diet breadth of P. pellucida based on the Shannon - Wiener function (H) computed from the IFS data H (_IFS) was -1.42. Food richness (i.e. food items with IFS ≥ 0.1%) observed, consisted of 12 food items with cladocera as dominant ranging from 17.17–35.4% and ceratopogon (Dipteran insect) of 0.1%, as the least. Feeding was most intense in April, (19%) closely followed by February (18.9%) and December (18.4%) while the least intensity of 0.2% was obtained in July. P.pellucida of all sizes fed most intensively on cladocerans with a steady increase in mean intensity from the smallest (4.1-5.0cm) size group (92.11) to a maximum (418.62) in the 8.1 – 9.0cm SL size class and declined thereafter. A similar trend in feeding intensity also occurred with algae ranging from 38.87 in the 4.1 – 5.0cm SL class to 182.24 in the 8.1 – 9.0 cm SL class.