© by PSP Volume 20 – No 8a. 2011 Fresenius Environmental Bulletin 2156 GRACILARIA VERRUCOSA (HUDSON) PAPENFUSS CULTURE USING AN AGRICULTURAL ORGANIC FERTILIZER İlknur Ak 1, *, Zerrin Çetin 1 , Şükran Cirik 1 and Tolga Göksan 1 1 Çanakkale Onsekiz Mart University, Fisheries Faculty, Terzioğlu Campus, 17100, Çanakkale, Turkey ABSTRACT In this study, the effect of an agricultural organic fer- tilizer on growth, pigment, proximate and agar content of Gracilaria verrucosa (Hudson) Papenfuss was studied. The highest daily growth rate was determined in the agricul- tural organic fertilizer group as 4.0 % day -1 . Therefore, the growth of G. verrucosa with agricultural organic fertilizer and Conway’s medium showed no significant differences (p>0.05). The maximum total chlorophyll content in the agricultural organic fertilizer was higher (20.7±1.5 µg g -1 ) than in Conway’s medium (7.0±0.2 µg g -1 ). The maximum protein (42.6 % dw) and lipid contents (7.6±0.1 % dw) were achieved in the agricultural organic fertilizer group. The significant differences were determined between the groups (p<0.05). The highest carbohydrate (58.1±0.4 % dw), ash (12.5±1.0 % dw) and agar (21.9±0.3 % dw) con- tents were found in Conway’s medium. There was a statis- tically significant difference between the experimental groups (p<0.05). Consequently, it was seen that the agricul- tural organic fertilizer is suitable for G. verrucosa culture to produce human and animal food in order to decrease the production cost, but it is unsuitable for agar production. KEYWORDS: Gracilaria verrucosa, agricultural organic fertilizer, growth parameters, proximate composition, agar 1. INTRODUCTION Red algal Gracilaria sp. is preferred for agar – agar production due to a high growth rate and easy culturing [1- 3]. The growth rate and chemical composition of Gracilaria is influenced by the culture medium [4, 5], epiphytes [6, 7], culture techniques, water quality (temperature, salin- ity, and pH), light intensity, water exchange and mixing rate [8-13]. Composition of the culture medium influences pigment composition, protein contents and agar amounts in Gracilaria [1, 11, 14]. Aiming to reduce the cost of culture medium, various studies have been conducted, in * Corresponding author which aquaculture effluents and salts from commercial- grade fertilizers and inexpensive nitrogen sources, such as ammonium salts and urea, were used [15-17]. A few stud- ies have been conducted to reduce production cost with use of agricultural fertilizers for seaweed cultures [18-21]. Gracilaria verrucosa (Rhodophyta) is naturally found at Turkish coasts, and the abundance of this red alga de- creases because of environmental factors and epiphytic algae [22]. Gracilaria should be cultured to prevent over- exploitation of natural stocks. There are several studies on G. verrucosa culture in Turkey [9, 10, 23] but no study has been found on the effect of the agricultural organic fertilizers on growth of this red seaweed. The aim of this study was to determine the effect of agricultural organic fertilizer on growth, pigment composition, proximate and agar content of Gracilaria verrucosa. 2. MATERIALS AND METHODS 2.1. Seaweed Material and Cultivation G. verrucosa thalli were collected in İzmir Bay (38 o 45’N, 27 o 05 ’ E), Turkey. The seaweeds were washed with seawater, and epiphytes were cleaned. The study was conducted in ellipsoid polyester tanks having 50 cm width, 100 cm length and 40 cm depth. The tanks containing 50 L seawater were placed in greenhouse. In order to avoid growth limitation, biomass density was kept approximately at 5 g wet weight (ww) per L throughout the culture period [11, 24]. Two experimental groups were set up in order to investigate the effects of organic agricultural fertilizer on cultivated seaweeds. The Conway’s medium was used in the first group (1 ml L -1 ) and agricultural organic fertilizer was used in the second group (1 ml L -1 ). The composition of the Conway’s medium and agricultural organic fertil- izer used in culture growth is given Table 1. The seawater and culture media were replaced once a week. 2.2. Measured Parameters The study was carried out from November 2007 to March 2008 (140 days). During the experiment, water tem- perature, salinity and light intensity were recorded weekly. Water temperature was measured by a hand thermometer, and salinity determined by a refractometer. Light intensity