Abstract

A growth trial was conducted to investigate the effects of dietary lipid levels on growth, feed utilization, condition factors, survival rate and carcass composition and to evaluate the lipid requirement of kutum fingerlings, Rutilus frisii kutum. Five isonitrogenous experimental diets were formulated to contain graded levels of lipid (50, 80, 120, 160 and 190 g kg^-1). After 2 weeks of the conditioning period, triplicate groups of 80 kutum (initial average weight of 0.50±0.07 g, mean±SD) were stocked in 250-l tanks and fed to apparent satiation thrice a day for 8 weeks. After feeding trial, the results showed that growth performance, feed efficiency and whole-body composition were significantly affected by dietary treatment. Growth performance generally improved with increasing dietary lipid from 50-120 g kg^-1 lipid diets and slightly decreased thereafter with further increase in dietary lipid. Food conversion ratio was negatively correlated with the dietary lipid (R² = 0.897). Protein retention efficiency and energy retention efficiency, generally increased with increasing dietary lipid level but lipid retention efficiency were inversely correlated with dietary lipid concentration (p<0.05). The carcass composition of kutum was affected by dietary treatments except for ash and protein contents. The carcass lipid of fish in this study was obviously increased corresponding to dietary lipid levels. The optimal dietary lipid level, estimated by polynomial regression analysis for maximum growth of kutum fingerling was 13.55%.

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INTRODUCTION

Dietary lipid is an important nutrient element for fish nutrition which supplies a source of energy and essential fatty acid (Sargent et al., 1989) and is also transporters of fat-soluble vitamins. Extreme lipid or carbohydrate (non-protein) energy sources in diet may have adverse influences on growth, reduce feed intake and inhibit the utilization of other nutrients and lead to increased fat deposition (Garling and Wilson, 1976; Winfree and Stickney, 1981). Use of appropriate dietary lipid level is prevented to employ the dietary protein for energy generation, resulting in higher specific dynamic action and will lead to a decrease in ammonia excretion and the feed costs (LeGrow and Beamish, 1986; Catacutan and Coloso, 1995). Protein sparing effect implies that inclusion of lipid and carbohydrate (non-protein) energy sources has been displayed to lower dietary protein employed for energy and elevate protein utilization for growth (El-Sayed and Teshima, 1992). Dietary lipid has been shown to provide a protein sparing effect in some fish (Santinha et al., 1999). The effects of dietary lipid level on growth rate, flesh quality, immune response, disease resistance and reproduction performance have been investigated in several species important in aquaculture (Luquet and Watanabe, 1986; Bromage et al., 1992; Regost et al., 2001; Chaiyapechara et al., 2003).

Fishing in Caspian sea concentrates mainly on two fish species: Kutum and Common carp, both being appropriate growth rate. But kutum, Rutilus frisii kutum (Kamenskii 1901) is a very popular food fish because of its good meat quality and good consumer acceptance especially in north of Iran. In recent decades, the natural reproduction of kutum has been limited and its artificial reproduction is successfully done in hatcheries (Abdoli, 1990).

In the restocking centers, larval rearing takes place in earth ponds and kutum larvae feed on zooplankton and formulated diet. The formulated diets are used in the form of paste and contain 28-35% protein and 8-10% lipid, based on the requirements for common carp (C. carpio L.) because nutritional requirements of this species are still unknown. Although, several studies have been conducted to appraise the nutritional parameters of kutum (Neverian et al., 2008; Neverian and Shabanipour, 2008), there is no accurate information on the dietary lipid requirement of kutum. Therefore, the present study was designed to evaluate the effect of lipid levels in a practical diet on growth rate, feed utilization and body composition of kutum figerlings, Rutilus frisii kutum (Kamenskii 1901).

MATERIALS AND METHODS

Experimental fish and rearing conditions: Kutum (Rutilus frisii kutum) fingerlings were obtained from Shahid Rajaee restocking center located in the southern coast of Caspian sea, Sari, Iran. After 2 week’s acclimation, kutum fingerlings with initial body weight of 0.5±0.09 g were randomly distributed into 250-l fiberglass tanks with 80 fish per tank. Each dietary treatment had 3 replications.

Water quality parameters were checked periodically, pH was found between 7.8-8.0; water temperature ranged from 19.7-23.2°C and dissolved oxygen was not <7.2 mg L^-1. Fish were hand-fed with the experimental diets until apparent satiation 3 times daily (7 days a week).

Diet preparation: Five isonitrogenous diets with 42% Crude Protein (CP) were formulated to provide five dietary lipid levels at 50, 80, 120, 160 and 190 g kg^-1 diet (dry basis). Gross energy content of each diet was calculated based on 23.4, 39.2 and 17.2 MJ kg^-1 for protein, lipid and carbohydrate, respectively. Feedstuffs were homogenized through a 1.0 mm sieve, blended in the computed ratios, moistened with distilled water (25% v/w) and pelleted in a grinder. The formulation and proximate analysis of experimental diets are shown in Table 1.

Sample fish and chemical analysis: At the end of the experiment, 20 fish from each tank were randomly sampled and euthanized by overdose of ethylene glycol monophenyl ether and kept frozen (-20°C) for determination of final whole body composition. The analysis of diets and fish samples followed standard AOAC (1984). Crude protein content (Nx6.25) was determined according to the Kjeldahl method after acid digestion using an Auto Kjeldahl System (1030-Auto-analyzer, Tecator, Hoganos, Sweden). Crude lipid was determined by etherextraction using a Soxtec extraction System HT (Soxtec SystemHT6, Tecator, Sweden). Ash was determined by muffle furnace at 550°C for 24 h. Moisture was determined by oven-drying at 105°C for 24 h.

Calculations: The performance parameters, body composition and survival percentage were calculated as below:

where, W_F and W_I are the mean final body weight and the mean initial body weight, T is the experimental duration in days.

Table 1:	Formulation and proximate composition of diets used in experiment
aPars kelika Co., Mirood, Iran; bHerring oil; cVitamin premix contained the following vitamins (each kg-1 diet): vitamin A, 10 000 IU; vitamin B6 20 mg; vitamin B12, 0.04 mg; biotin, 0.2 mg; choline chloride, 1200 mg; folic acid, 10 mg; inositol, 200 mg; niacin, 200 mg; pantothenic calcium, 100 mg. dContained (g kg-1 mix): MgSO4.2H20, 127.5; KCl, 50.0; NaCl, 60.0; CaHPO4.2H2O, 727.8; Ca (IO3)2.6H2O, 0.295; CrCl3.6H2O, 0.128. eSigma, St. Louis, MO, USA.. fNitrogen-Free Extract (NFE ) = 1000-(protein+lipid+moisture+ash). gBased on 23.4 kJ g-1 protein, 39.2 kJ g-1 lipid and 17.2 kJ g-1 NFE. hProtein/Energy ratio (g MJ-1)

Statistics: The data were subjected to one-way ANOVA and correlation analysis where appropriate. Multiple comparisons among means between individual treatments were made with Duncan’s multiple range tests. The significance level was at p<0.05. All statistical analyses were performed using SPSS Base 16 for Window.

RESULTS AND DISCUSSION

The survival rates were generally high from 95.00-99.58% over the 8 weeks trial and it was affected by the differing dietary lipid level of the diets (p<0.05). The lowest percent survival was observed for fish fed the diet containing 50 g kg^-1 lipid diets. Growth rate and feed efficiency were significantly affected by dietary lipid content of the diets (Table 2). Growth performance (final body weight and SGR) generally increased with increasing dietary lipid from 50-120 g kg^-1 lipid diets. The highest growth performance (p<0.05) was achieved in kutum fed the diet containing 120 g kg^-1 lipid. The FCR of the kutum was significantly affected by dietary lipid level (p<0.05). FCR was negatively correlated with the dietary lipid (R² = 0.897). The high levels of dietary lipid seemed to have significantly effect on FCR (p<0.05). When the dietary lipid level was higher than 120 g kg^-1 lipid diets, this nutrient no showed significant effect on FCR (p>0.05). Protein efficiency and feed efficiency were improved as increasing of dietary lipid level. FER of fish fed on dietary lipid levels 120, 160 and 190 g kg^-1 lipid was not different (p>0.05). FI and PI decreased significantly (p<0.05) with increasing dietary lipid level and lipid intake tended to decrease with the decline of dietary lipid level. Kutum fed the diet with 190 g kg^-1 lipid had the highest PRE among the dietary treatments. However, the lowest values for both parameters were recorded in fish fed the diet with 50 g kg^-1 lipid.

At the end of the experiment, moisture, lipid and energy contents in body composition of fish were significantly affected by dietary lipid levels (p>0.05) while crude protein in carcass was not affected by dietary treatments (p<0.05) (Table 3). Crude lipid and energy contents in carcass of kutum had increased, when dietary lipid was increased from 50 g kg^-1 lipid diets to 190 g kg^-1 lipid diets but moisture contents in carcass tended to decrease with the increase of dietary lipid level and same trend was observed for ash contents, meanwhile it was not significantly affected by dietary lipid level (p<0.05).

Dietary lipids are important nutrient affecting energy production in most of fish. They are well utilized by fish and essential for common growth and development.

Table 2:	Growth response and feed efficiency of kutum fed the diets containing different lipid levels for 8 weeks
Mean values and Standard Deviation (±SD) are presented for each parameter (Three groups per treatment). Means in the same line with different letters are significantly different (p<0.05). FCR: Food Conversion Ratio; SGR: Specific Growth Rate; FER: Feed Efficiency Ratio; PER: Protein Efficiency Ratio; FI: Feed Intake; PI: Protein Intake; PRE: Protein Retention Efficiency; EI: Energy Intake

 

Table 3:	Carcass composition of kutum fed the diets containing different lipid levels
Initial body composition: bodies of 50 fish (means±SD) were used for statistical analysis. Final body composition: values are means of three groups per treatment. Values in the same column with different superscripts are significantly different (p<0.05)

 

 

Fig. 1:	Relationship between percent weight gain and dietary protein level for kutum fingerlings as described by second-polynomial regression

 

However, fish are known to utilize protein preferentially to lipid or carbohydrate as an energy source. The results of this trial based on feeding dietary lipid levels from 50-190 g kg^-1 lipid diets indicate that survival rate varied 95.00-99.58%. The optimal dietary lipid level, estimated by polynomial regression analysis, for maximum growth of kutum fingerling was 13.55% (Fig. 1). The results showed that the increase in dietary lipid level from 50-120 g kg^-1 lipid diets increased growth and slightly decreased thereafter with further increase in dietary lipid. In this study, the highest specific growth rate of kutum (500 mg initial weight) was 2.54% day^-1 which is good score compared to other researches. For instance, Haghighi (2006) registered maximum SGR of 2.78% day^-1 for kutum fry (200 mg initial weight) fed a diet containing 468 g kg^-1 protein and 80 g kg^-1 lipid.

Some fish especially carnivorous species (most marine fish and marine crustacean) can employ higher dietary lipid for optimum growth rate (Peres and Oliva-Teles, 1999; Lopez et al., 2006). On the other hand, some researchers have reported that high dietary lipid level may be depressed fish growth (El-Sayed and Garling, 1988). This reaction may be due to decrease in feed intake, excessive lipid deposition in visceral organs to decrease in the efficiency or activity of digestive enzymes (Tocher, 2003). Likewise, Baker and Davies (1997) reported that growth depression in high dietary lipid level could be due to increased malonaldehyde in oxidized lipid which is poisonous to fish. In the present study demonstrated that the increase in dietary lipid level was collaborated with a reduction in feed intake, probably because fish eat to satisfy their energy requirements.

Feed and protein efficiencies at the present study tended to improve with increasing level of dietary lipid. It implies that kutum fingerlings have a relatively good ability to utilize dietary lipids as energy sources. Appropriate quantities of lipid and/or carbohydrate sources (non-protein energy) in the fish diet can minimize catabolism of protein (Cho and Kaushik, 1990). Lipid as energy source has been shown to provide a protein sparing effect in some fish (Sargent et al., 1989; Skalli et al., 2004).

In the present study, the FCR of experimental diets varied 1.77-3.50. The lowest dietary lipid level (50 g kg^-1 lipid diets) produced the highest FCR, probably due to the intake of insufficient nutrient levels to promote growth. The best FCR was observed in fish fed diet containing 190 g kg^-1 lipid diets.

The carcass composition of kutum was affected by dietary treatments except for ash and protein contents (Table 3). This effect has previously been observed in other fish species and aquatic animals (Cho et al., 2001; Sa et al., 2006). Very high dietary lipid levels might result in excessive lipid aggregation in the visceral cavity, tissue and liver and might consequently increased the whole body lipid concentrations (Tocher, 2003). The carcass lipid of fish in this study was obviously increased corresponding to dietary lipid levels. A slight increase in body protein contents with the increase of dietary lipid level was also observed in kutum but increase in body protein content was not significantly different among the treatments.

CONCLUSION

In this study, whole body moisture was inversely related to whole body lipid content and a mutual relevance between lipid and moisture has been reported in many fish in general (Parazo, 1990). Based on the results of this study, the maximum growth of kutum fingerling was observed when fed the diet containing 120 g kg^-1 lipid diets and the protein/energy ratio was approximately 21.68 g MJ^-1. From the polynomial regression analysis, the optimal dietary lipid requirement of kutum was estimated to be 13.55%.

How to cite this article:

H. Ouraji and G. Ebrahimi. Dietary Lipid Requirement for the Kutum Fingerlings, Rutilus frisii kutum (Kamenskii 1901).
DOI: https://doi.org/10.36478/rjnasci.2011.1.5
URL: https://www.makhillpublications.co/view-article/1993-5269/rjnasci.2011.1.5