Differences in Growth Rate of African Catfish (Clarias Gariepinus) And Plankton Diversity Between Ponds Fertilized by Organic and Inorganic Fertilizers

Abstract

Aquaculture offers opportunity for safeguarding local and global food security in the face of declining capture fisheries. However, agrochemicals used in aquaculture negatively impact biodiversity through pollution effects such as eutrophication which is associated with fish kills. The main argument for the use of agrochemicals in aquaculture is to enhance productivity. However, evidence is lacking on whether use of inorganic fertilizers enhances fish productivity than organic fertilizers. Furthermore, effects of pollution from inorganic fertilizers have been demonstrated in aquatic ecosystems but not under aquaculture conditions. The main objective of the research was to investigate growth rate of Clarias gariepinus, an important aquaculture fish in Kenya, and plankton diversity between ponds fertilized by organic and inorganic fertilizers. Specific objectives of the study were to determine differences in growth rate of C. gariepinus and plankton diversity in ponds fertilized using chicken droppings and in ponds fertilized using Diammonium phosphate (DAP) and urea. Fish were raised in five ponds: two inorganic ponds were fertilized by DAP and urea, two organic ponds were fertilized by chicken droppings, and one pond was not fertilized and served as a control. Fish in all ponds were given supplementary feed at the same rate. Growth rate was determined by measuring weight (g) and total length (em) fortnightly for four months. Average growth rate in length was higher in the organic pond at O.06cm/day, followed by inorganic pond at 0.05cm/day and control at 0.04cm/day. Average growth rate in weight was higher in organic pond at 0.08g/day, followed by inorganic pond at O.07g/day and control at 0.06g/day. Although differences in growth rate of fish in organic and inorganic ponds were not significant, fish in fertilized ponds were on average longer and weighed more than those in the control pond. These results suggest that pond fertilization is important but the argument that productivity is higher in ponds fertilized using inorganic fertilizers was not supported. Plankton identification was done using standard microscopic methods. Jaccard's similarity index for phytoplankton was highest (0.38) between organic and control but lowest (0.25) between inorganic and control suggesting that the use of chicken droppings did not shift nutrient balance in the ponds as did DAP and urea. Use of chicken droppings produced the highest diversity of zooplankton (Shannon- Weiner's H in organic pond = 1.886; inorganic = 1.044, and control = 0.935). The use of DAP and urea produced the highest proportion of phytoplankton species associated with pollution. In conclusion chicken droppings should be used to fertilize ponds for higher growth rate of C. gariepinus and to reduce pollution in aquaculture systems. Overall the study demonstrates that the use of Inorganic fertilizers is not associated with higher productivity than organic manure and may result in toxic algae thus the use of such fertilizers in aquaculture should be avoided.