ECONOMIC EVALUATION OF RAINBOW TROUT (Oncorhynchus mykiss) FARMING FED WITH DIFFERENT COMPOSITION FEED

Th is paper evaluates the eff ects of two diff erent feeds on production results and economic performance in the rainbow trout (Oncorhynchus mykiss) farming. Th e fi rst group (O-1) was fed with a standard complete pelleted feed, and the second group (O-2) was fed with combined feed consisting of 75 % pellets and 25 % of sardines. Better results were obtained with the O-2 group, while the O-1 group achieved results characteristic for local farming conditions and feed quality. Experimental group O-2 had signifi cantly higher (p<0,01) growth rate when compared to group O-1. Considering current feed and fi nal product (fi sh) prices in the market, better results in terms of cost-eff ectiveness were obtained (E>0,00) in O-2 group of trout fed with the combined meal.


INTRODUCTION
Fish production as well as nutrition has developed signifi cantly in recent years (Azis at al., 2011). Good nutrition in animal production systems is essential to economically produce a healthy, high quality product. In fi sh farming, nutrition is critical because feeding represents almost half of the production costs.
Rainbow trout is one of the most important Salmonide species of major economic interest for commercial culturing worldwide and it is the dominant type of trout farming in the Balkans (Vranić, 2012). Th e type of feed and the feeding process itself are among the most important factors infl uencing trout growth, feed utilization and tissue composition in intensive production. Salmonide feed costs constitute more than 40% of the production cost (Azevedo P. A., 2004). Th us, much work has been done to create the optimal nutritional requirements, feeding process, growth and feed conversion ratios of salmonids (Okumus at al., 2002). Much eff ort has been and is still put into creating feed composition best for developing balanced commercial diets that promote optimal growth and health with minimal production cost.
In order to make production cheaper in intensive farming system, it is necessary to provide cost-eff ective feed which can satisfy trout biological and nutritional needs. Cost-eff ective feed is achieved by introducing raw material substitute for more expensive feed (Weatherup R.N., 1997, Kiang, 1999, Sredanović et al., 2002. Due to the importance of increased production in salmonidae intensive farming system, in this study we evaluated the eff ects of substituting expensive pelleted feed with a cheaper one, and its impact on the economics of rainbow trout production.

MATERIALS AND METHODS
A 90 day feeding trial was conducted in rainbow trout pond with all necessary facilities for trout culture farming. Th e pond is located at an altitude over 200 m and is supplied by quality water from a river source by direct gravity. Rainbow trout (Oncorhynchus mykiss-Walbaum) with the average weight of 90 g and length of 190-210 mm was used in the experiment. Th e fi sh were divided into two experimental groups, O-1 and O-2, and placed in the separated pools, 1 320 trout in each one.
Th e experimental group O-1 was fed with a standard pelleted mixture, while the experimental group 0-2 was fed with mixture of 75% pellets and 25% sardines. At the beginning of the experiment the length and average weight of the fi sh were recorded, and at the end of experiment the weight gain, feed intake, feed conversion ratio (FCR), and the economics of production were examined.
According to the feed formulation specifi cation and crude cost, the price of one kilogram feed for each group was calculated. Economic indicators (cost-effi ciency, the cost price and the fi nancial results) were calculated at the end of experiment over actual values and costs of production. Retail prices of certain raw materials used for the feed preparation were taken from the last quarter of year 2015, as well as the retail price of fi sh on the market.
Th e price of one kilogram of feed (pellets), for O-1 experimental group was 135,00 dinars, while the price of one kilogram of feed for O-2 experimental group was 115,00 dinars (750 gr of pellets and 250 gr of sardelas). Retail price for one kilogram of trout was 600,00 dinars.
Th e calculation of fi sh farming cost has been evaluated so that the amortization costs, farm staffi ng cost, indirect costs, costs of starting material and other costs (electric energy, water aeration) were fi xed for both groups, but only the cost of feed was variable.
Th e obtained results were analyzed using descriptive statistical values. Descriptive parameters such as arithmetic mean, standard deviation, variation interval, coeffi cients of variation were used. Statistically signifi cant result between experimental groups was evaluated based on p value.
Statistical analysis of the results was elaborated using soft ware GrapfPad Prism version 5.00 for Windows, GrapfPad Soft ware, San Diego, California USA, www.graphpad.com. Th e results were summarized in tables and charts.

RESULTS
Th e trout weight gain in both groups over 90 days trial are shown in Chart 1. At the beginning of the experiment the average weight of trout in both groups were comparable, so there was no signifi cant diff erence (p>0.05) between them. However, throughout the experiment a diff erence in the average trout weight occurred and by the end of the experiment the more weight was obtained in 0-2 group ( = 156,78±23,31). Th e average weight of trout in O-1 group was ( = 134,68±19,80).
Th e diff erence of the average weight of trout in the 0-2 group compared to the average weight in 0-1 group was 22,10 grams and it was statistically signifi cant (p<0,01) ( Table 1). Changes in the total and daily weight gain and feed intake of trout in both groups is shown in Table 2. Th e better growth was achieved by trout in 0-2 group, with total weight gain of 67,80 g or 0,75 g per day, which is signiffi cante higher growth than the O-1 group trout (p<0,05).

Chart 2. Total weight gain and total feed intake ratio
At the end of the experiment the total and daily feed intake of trout in 0-2 group was 78.38 and 0.86 g respectively. Th e less satisfying results regarding total weight gain were obtained in the O-1 group, where the total and daily feed intake was 87,89 g and 0,98 g respectively. Th e better feed conversion ratio was achieved in the 0-1 group (1,16).
Feed costs were calculated as the result of price and quantity of feed used (O-1 group 13.349,00 dinars.; O-2 group 10.394,00 dinars). Production value was calculated as the result of the gained fi sh weight (O-1 group 106.667,00 dinars, O-2 group 124.170,00 dinars) and retail fi sh price per kilogram (600,00 din/kg). Th e fi nancial result is the diff erence between production value and production costs, and cost-eff ectiveness is a ratio between the value and cost.

DISCUSSION
Optimal feeding is considered as one of the most important factors in intensive farming systems, whereby fi sh growth is entirely dependent upon the external provision of a nutritionally complete high quality diet (Tacon and al., 1997).
Common problem facing fi sh farm operation is the need to obtain a balance between rapid fi sh growth and optimal use of the supplied feed (Gokcek et al., 2008). Since the feed cost accounts approximately for 40-60% of the operating costs in intensive farming systems (Agung, 2004), the economic viability of the farming operation depends on the feed composition, its nutritional value as well as price of raw materials used in the feed preparation. Although biological needs of fi sh in terms of protein, energy, vitamin and mineral composition of meals are established, researchers are changing the composition of meals, depending on the types of nutrients available, their costs, production process, and the physical characteristics of the pellets used in order to get the best and economical fi nal production results (Alanara, 1992;Tacon, 1993;De Silva et al. 1995).
Th e goal of this study was to determine the eff ects obtained by using two diff erent type of feed in rainbow trout (Oncorhynchus mykiss) farming. Th e production cost were analyzed, and the results of experimental groups have been compared. Food for the experimental group O-1 consisted of trout pellet mixture with standard raw material composition that provided all the essential nutrients as recommended for this trout category (NRC, 1993). Feed for the 0-2 group had a wider ratio of proteins both of animal and plant origin and a lower amount of energy. Based on the trout weight at the beginning and at the end of the experiment, the total and daily weight gain in both groups were calculated.
Th e achieved results showed that there were signifi cant diff erences between the 0-2 group and the O-1 group (p < 0.05). Results of average daily weight gain of trout in other studies ranged from 0,7 to 1, 2 g ( Kulišić and al., 1987;Mijailović et al., 1990;Apostolski et al., 1983;Dalbelo, 1986). However, daily weight gain in our experiment with combined meal was 0,75 g, and according to Kulišić et al. (1986) daily weight gain was 0,66 g, while Mijailović et al. (1990) examining the impact of the combined meal (pellet +/-fi sh guts) on the performance achieved higher daily weight gain ( 2,14 g) compared to our results.
Feed conversion ratio is one of the best indicators of production eff ectiveness as well as the feed quality infl uence on the achieved weight gain. Feed conversion ratio in O-1 group was 1,92 and in O-2 was 1,16. According to the results of Kulišić et al. (1986) who examined the eff ect of combined meal (pellet + worms), the feeding coeffi cient of 1,31 was achieved, which is slightly lower than the result obtained in our experiment where meal based on pellets + sardines (1,16) was used. Steff ens (1994) research showed that poultry byproduct feed is suitable as a partial or complete replacement, but that complete substitution of feed by poultry by-product and feather meal resulted in reduced weight gain and feed utilization. Fish fed diets with 27% combined poultry by-product and feather meal without amino acid supplementation had feed conversion ratio of 1,15.
Considering obtained results it can be concluded that trout feeding with combined meal (pellet + sardines) has nutritional and biological justifi cation. Th e feeding coeffi cient in the O-1 group fed with a standard pelleted food was similar to the results obtained by Apostolski et al. (1983)