Feeding in fish ponds is meant to increase fish productivity and this is almost always achieved. What we do not know is the impact of this practice on benthic freshwater invertebrates and the ecosystem as a whole.
Once every four weeks for three months (December to February), benthic soil samples were collected from 24 identical fish ponds stocked with channel catfish-Ictalurus punctatus. Half of these ponds were fed ponds and the other half unfed ponds. The amount of feed added per pond was 40kg/ha on 12 occasions. We were interested in elucidating the impact of fish feed on the biomass productivity and diversity of macroinvertebrates.
Benthic soil samples were collected using a Perschbacher sampler. Four samples were collected per pond and 4-corer samples constituted one composite sample. The macroinvertebrates were extracted from 100ml soil, using a sieving and decanting technique. For analysis purposes the macroinvertebrates were grouped into their respective phyla and a paired-t test was used to analyze the data, fed versus unfed. The mean values for the three months period were used for the analyses. Temperature and pH values were also obtained.
Results/Conclusions The three macroinvertebrate phyla recovered from the samples were Mollusca, Annelida, and Arthropoda, respectively. The mean number of macroinvertebrates per 100ml of soil recorded for the fed and unfed ponds was 174.1 vs 406.4, 159.4 vs 191.6, and 0 vs 46.2, respectively for the Mollusks, Annelids, and Arthropods. The statistical analyses for the Mollusks and Annelids show that these differences are highly significant at P>0.001, for all two phyla. This translates into approximately 133.4% and 20.2% population density reduction in the respective phyla by the fish feed. The elimination of the Arthropods in fed ponds results in both biomass and species diversity reduction. The mean pH values during the investigation were 5.1 vs 6.8 respectively for the fed and unfed ponds. A drop in the pH in the fed ponds may be partly responsible for this observation.
We conclude that fish feed drastically suppresses biomass productivity and diversity of macroinvertebrates. These could have serious consequences for the aquatic ecosystem in the long-term.
