PHYTOPLANKTON ABUNDANCE AND BIOMASS IN FERTILIZED EARTHEN FISH CULTURE PONDS OF RASHT , IRAN

The effects of both granular and liquid fertilizers on phytoplankton abundance and biomass under fish culture pond conditions were studied. Six fish ponds (1000 m) were designated for the experiment. Ponds were treated using granular fertilizers (GF) and liquid fertilizer (LF). The fertilization rate was 1 mg/l nitrogen and 1 mg/l phosphorous over a 10 days interval for 10 weeks. The chlorophytes, bacillariophytes and chrysophytes demonstrated a significant difference between LF and GF treatments, whereas there appeared to be no meaningful difference in terms of the population of cyanophytes and euglenophytes. Introduction A fish pond constitutes a small ecosystem that is comprised of physical-chemical factors, primary producers, consumers and detritus, with complicated ecological bonds among them. Pond fertilization implemented by fish farmers may increase phytoplankton biomass, thereby altering water transparency and conditions for other primary production development (Broyer and Curtet 2011). This tends to be followed by an increase in zooplankton prey for carp (Wurts 2004) and macro-invertebrates. Recently, there has been a renewed interest on the role of fish in food cycles and energy supply within fish ponds. The use of granular fertilizers is replacing the use of synthetic liquid fertilizers for the production of warm water fish and shrimp species in the leading fish farming countries. However, Seidavi et al. (2014) and Tizkar et al. (2014) suggested that liquid fertilizers have several advantages over the traditionally used granular inorganics. There is a lack of data comparing the relative effectiveness of liquid and granular fertilizers in earthen ponds. The objective of this study is to compare the effects of both granular and liquid fertilizers on phytoplankton abundance and biomass under fish culture earthen pond conditions. Materials and Methods The experiment was carried out at the Bony Fish Hatchery Complex in Rasht, Iran (37o13'23.17"N; 49o36'18.68"E). Six fish earthen ponds (1000 m each) were designated for the experiment. The pond Nos. 1, 3 and 6 were fertilized using nitrogenous and phosphorus granular fertilizers (GF), whereas pond Nos. 2, 4 and 5 were treated with liquid fertilizer (LF). There were 2 treatments, including 3 replications per each treatment. Treatment 1 included GF and treatment 2 included LF. The ponds were equal in size and shape and each were 1.1 m deep. All of the ponds underwent similar preparations. To disinfect the farming ponds, 200 kg of quicklime was used in each pond. Water was introduced into the ponds, with water flowing through protective filtration nets. The GF involved the use of granulated triple phosphate fertilizer and urea fertilizers, whereas the LF group had a fertilization rate of 1 mg/l nitrogen and 1 mg/l of phosphorous at 10 days intervals. *Author for correspondence: . University of Nayarit. Coastal Bioengineering Laboratory. Nayarit. México. 63155. Gilan Agricultural and Natural Resources Research and Education Center. Agricultural Research, Education and Extension Organization (AREEO). Rasht. Iran. Applied Scientific Higher Education Institute, Jehade-EAgriculture, Tehran, Iran.