International Journal of Science and Applied Technology IJSAT, Vol. 2, No. 2, 2017 http://ijsat.unri.ac.id 19 Nitrogen-Phosphorus Load Contributed by Common Carp (Cyprinus carpio L.) Floating Net Cages in Lake Maninjau Indonesia: A Comparison of Floating and Drowned Feed Type Hafrijal Syandri 1* , Azrita 1 , Ainul Mardiah 2 1 Department of Aquaculture, Faculty of Fisheries and Marine Science, Bung Hatta University, Padang, Indonesia 2 Department of Aquaculture, Faculty of Marine and Fisheries Science, Nahdlatul Ulama University of West Sumatera, Padang, Indonesia syandri_1960@yahoo.com *Corresponding author Abstract: Lake Maninjau is one of the most important locations for fish aquaculture activities with floating net cages in Indonesia. The objective of the research was to compare the nitrogen (N) and phosphorus (P) loads into Lake Maninjau by Cyprinus carpio from floating and drowned feed type. Cyprinus carpio fingerlings (initial weight 56.79 ± 1.77 g) was collected from a private hatchery in Rao-Pasaman Timur. The study was conducted at two locations in Lake Maninjau, i.e. Farm I and Farm II. Each farms consisted of three units of floating net cage with floating and drowned feed. Each floating net cage has 32 m 3 (4x4x2 m) capacity and individual stocking density of 150 m -3 . Approximately 1,500 kg feed was used in each floating net cages during the experiment each time. The total N load into water bodies from floating and drowned feed both farms were 47.32±6.18 and 39.24±0.09 kg tonˉ¹ fish production, respectively. Whereas the total P load into water bodies from floating and drowned feed were 18.47±0.72 and 18.25±1.15 kg tonˉ¹ fish production, respectively. Drowned feed is preferred for aquaculture activity in floating net cages at Lake Maninjau. Since it minimizes eutrophication process, while maintaining a sustainable aquaculture activity. Keywords: Aquaculture, Cyprinus carpio, floating net-cages, feed type, N P mass balance. 1. Introduction The total organic matter and other nutrients added to aquaculture production systems from fish feed that is not recovered in biomass of the culture species was defined as waste load [1]. The waste load causes water quality deterioration within the culture system [2, 3]. The waste load on the aquaculture operations can be sourced from fish feed [4]. Boyd and Tucker [5] found that 80% or more of the feed is consumed by fish, but 10 to 20% of the feed consumed becomes feces and is excreted into the culture system such as nitrogen (N) and phosphorus (P). It is depends on diets composition [6], type of feed [7], fish species [8], feed conversion ratio [9], and fish mass mortality [2]. Lake Maninjau is a tecto-volcanic area spanning 99.5 km 2 . It has an important roles as a floating net cages operations and as fisheries capture area, besides being used for tourism destination, and hydroelectric power plant [10, 11]. There was an increase the number of total floating net cages over the years in 2011 (15,000 units), 2012 (15,860 units), 2013 (16,120 unit) 2014 (16,580 units) and 2015 (20,608 units) [10, 11, 12]. The common fish species cultured in Lake Maninjau were Common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus) [13]. The aims of the study to estimate the quantitative of the N and P loads released from Cyprinus carpio cultured on floating net cages in Lake Maninjau. The results of this study can increase the scientific understanding of the effects of different fish species release the levels of N and P into water bodies of Lake Maninjau. 2. Material & Method 2.1. Study Area The study was conducted in Lake Maninjau of West-Sumatera Province, Indonesia. The geographical position is S: 00⁰12'26.63"-S: 00⁰25'02.80" and E: 100⁰07'43.74"-E: 100⁰16'22.48". It is located at an altitude of 461.50 m above sea level with 99.5 km² surface area [10]. Based on the Schmidt-Ferguson climate classification, Lake Maninjau has characteristic of climate types A and an annual rainfall of 3,490 mm.