A three month preliminary study was carried out from December 2006 to February 2007, to investigate the effects that feeding has on benthic nematode community structure. Twenty identical freshwater fish ponds were investigated, 10 were feeding ponds and the other 10 were unfed ponds. All ponds were stocked with catfish and the fed ponds were fed with 32% floating catfish pellets. Each pond was divided into two and one-composite sample collected from each part. Each composite sample was made up of 4-corers. Two composite samples were therefore collected from each pond and each was collected 1.5m away from the shoreline. The temperature of each sample was determined in the field using a bi-metal dial thermometer. In the laboratory, each composite sample was mixed and homogenized. 50 ml was taken and prepared for pH determination and 100mL was taken for nematode extraction. Nematodes were extracted using a combination of decanting sieves and the Baermann funnels methods. Nematodes were incubated for 72 hours and a 15ml filtrate collected for nematode quantification and identification. After the nematodes of each sample were quantified, the sample was centrifuged and the pellet used to make a temporary slide. At least 100 nematodes were systematically identified and this number was adjusted to the total number of nematodes in the sample. The mean values were used for all analyses.
Results/Conclusions
The results showed that nematodes of all trophic levels were recovered i.e bacterivores(58.1%), fungivores(15.9%), herbivores(8.1%), omnivores(13.2%) and carnivores(4.7%), irrespective of pond treatment. Without exception, the unfed ponds consistently recorded higher nematode populations than the fed ponds in all trophic groups. For example the unfed ponds recorded 4x, 4.2x, 4.3x, 4.4x, and 1.5x more bacterivorous, fungivorous, herbivorous, omnivorous and carnivorous nematodes, than the fed ponds. Nematode populations decreased from December through February and so did the pH and temperature, irrespective of treatment and trophic guilds. It is concluded that fish feed has a suppressive effect on nematode populations and the benthic soil food web in general.
