Effect of dietary lipid levels on growth performance of Sea bass (Dicentrarchus labrax) fingerlings

 

European Sea bass (Dicentrarchus labrax) is an important commercial fish species in Mediterranean Aquaculture where it reach up to 20% of total fish production (Torrecillas et al., 2007).Although, the production of this species for stock enhancement is now a well- controlled process that results in the release of hundred of thousands of fingerlings annually, nevertheless , the nutritional requirements of this species have not been well defined (Kent et al., 2001) More information of this carnivorous marine species is needed to improve growth and feed efficiency and to minimize waste outputs to ensure  economical and environmental sustainability of sea bass culture (Drawbridge and Kent, 2001). Dietary lipid plays a major role in providing a source of  energy and essential fatty acids, especially for carnivorous fish as these species have a limited ability to utilize carbohydrates as an energy sources (Oliva-Teles 2000; Sargent et al., 2002, Kim and Lee, 2005). The increase in digestible energy content of fish diets, by lipid supplementation, has been shown to have a protein sparing effect, therefore reducing nitrogen losses to the environment (Cho and Bureau, 2001). Several studies have shown that providing adequate energy with dietary lipids can minimize the use of more high-priced protein as an energy source (Peres and Oliva-Teles, 1999, 2001; Ai et al., 2004; Hung et al., 2004; Kim and Lee, 2005). Therefore, an adequate lipid level in the diet is important for the growth performance of fish and product quality (Hamre et al., 2004; Tibbetts et al., 2005).      

The objective of the present study was conducted to determine the effects of dietary lipid levels on growth performance, feed efficiency and body composition of Sea bass fingerlings.

 

Four isonitrogenous diets were formulated (Table 1). They were based on fish meal and Soy bean meal as the protein source. These diets formulated to containing four lipid levels 10%,12%,14% and 16% ( fish oil and corn oil) ,respectively (Table 1). The diets were pelleted using grinder of kitchen aid with a 1.5 mm diameter and kept frozen until they used. Diets and body composition without viscera were analyzed for crude protein, crude lipid crude fiber and ash according to AOAC (1995) as shown in Table 2 and 5.

During the growth period (120 days), each diet was randomly allocated to triplicate tanks of fish. Feed was offered by hand in two meals / day (8:00h and 15:00 hours) at 3% of body weight and the amount of diets were readjusted after each weighing.

 

Table (1): Composition of the experimental diets

   1. 1-Vitamin mixture (per kg feed): 10000 I.U. Vit. A, 1000 I.U. Vit. D₃, 50 mg Vit. E,

   100 mg Vit. B₁, 100 mg Vit. B₂, 100 mgVit. B₆, 10 mg Vit. B₁₂, 20 mg Vit. K₃, 200 mg Vit. C,

   500 mg Nicotinic acid, 500 mg Inositol, 200 mg Ca-Pantothenate, 20 mg Folic acid,

   5000 mcg Biotin and 2000 mg Cholinchloride.

   2-Mineral mixture (per kg feed) : 16.40 g Monocalciumphosphate, 5.50 mg MgSO₄. 7H₂O,

   7.53 g NaC1, 4.50 g K₂SO₄, 2.0 g Fe-Gluconat, 0.40 g ZnSO₄.7H₂O, 50 mg MnSO₄. H₂O,

   15 mg CuSO₄, 4.75 mg KJ and 0.25 mg CoCl₂.6H₂O.

 

   Table (2): Proximate analysis of the experimental diets

      1. Nitrogen free extract.

      2. Based on 5.65 Kcal/g protein, 9.45 Kcal/g fat and 4.1 carbohydrate Kcal/g (NRC,1993)

      3. Mg Protein/ Kcal/kg

 

Sea bass fingerlings were obtained from Ashtom El gamel, Port-Said governorate. Fish were acclimated to laboratory conditions for 2 weeks before being randomly distributed into fiberglass tank of 300-L water capacity. Fish of 1.2±0.2 g initial body weight were distributed into 12 experimental tank (300L) in triplicate groups of 250 fish each.  Water temperature was maintained at 25ºC by a 250- watt immersion heater with thermostat. Water temperature and dissolved oxygen were recorded daily (by metteler Toledo, model 128.s/No1242), Other water quality parameters including pH and ammonia every two days by pH meter (Orion model 720A,s/No 13062) and ammonia meter (Hanna ammonia meter). The salinity was measured be refractometer. The average water quality criteria of all tanks are presented in Table 3.The experiment was lasted for 120 day. All fish in each tank were weighed every 10 days.

     Weight gain, feed intake, feed conversion ratio, protein efficiency ratio, liver weight, hepatosomatic index, liver fat and survival were calculated. Also, economical evaluations for the experimental diets were determined.

 

Table (3): Average water quality parameters in the experimental tanks 

    *Means ±SD.

One-way analysis (P≤0.05) of variance (ANOVA) followed by Duncan's multiple range test (1955) was used to compare means of the four different groups. All statistical were performed using (SPSS. Inc., Chicago, 12). The used model was Yij =µ+Ti + eij

      Where

       µ = over all mean.  

      Yij =the observation of the individual from T treatments           

      Ti= the fixed effect of T the diet.

Eij= the experimental random error associated with individual J.

 

The growth performance of Sea bass fingerlings which fed different diets are shown in Table 4. Average body weight (g) of Sea bass fed experimental diets at the start did not differ, indicating that groups were homogenous. At the end of the experimental period (120 days) the group of fish fed 14% lipid, had a significantly (P≤0.05) higher body weight gain than the rest of experimental groups. The lowest body weight (12.3 g) was achieved by group of fish fed lipid level 10%. On the other hand, the group of fish fed on 14% and 16% lipid levels had a significantly (P≤0.05) higher SGR than the rest of experimental groups. However, SGR were 1.94, 2.04, 2.19 and 2.13 for groups of fish fed on diet containing 10, 12, 14 and 16% lipids, respectively. The PER and FCR and their FE  of group of fish fed on 14% lipid level was significantly (P≤0.05) improved in comparison with fish fed on 10% and12% lipid level followed by group of fish fed on 16% level of lipid. Survival rate was taken also the same trend. These results are in agreement with Shkaras et al (1989). They reported that the optimum dietary lipid level for Asian seabass fingerlings between 15-18%. However, increased dietary lipid level to more than 16% did not improve weight gain, SGR, and PER of sea bass fingerlings. Some authors reported that high dietary lipid level may depress growth in some species (Pei et al., 2004; Du et al., 2005). Other fish spices, Asian and Japanese sea bass have shown that the requirement of lipid around 17% (Williams et al., 2003 and Ai et al., 2004).

 

 

The growth reduction at high lipid levels could be due to the limited ability to digest and absorb high amounts of lipid, a reduction in feed intake, excess lipid accumulation in liver and other visceral organs, or creation of dietary or metabolic imbalances (Luo et al., 2005).

 

Table (4): Growth performance, liver fat content of Sea bass fed the experimental diets.

*Average values of fish weight and feed intake (means ± S.E.M) were used as experimental units for the statistical analysis of growth performance.

**Average of liver weight and liver lipid (means ± S.E.M) were calculated from 10 fish.

***. Means in the same line not sharing a common superscript letter are significantly different (P≤0.05).

 

The FCR were significantly lower (P≤0.05) for fingerling sea bass fed a diet containing 14% lipid than the rest of experimental groups. The FCR values were compared favorably to FCR observed in other studies with marine fish (Williams et al., (2003). The fish with the higher growth consumed more feed and consumed a high amount of lipid than the fish fed the high lipid diet. Because protein retention is generally regulated by non-energy input of the diet, PER is a good measure of the "protein sparing effect" of lipid (Lie et al., 1988). The group of sea bass fingerlings fed diets containing 14 and 16% lipid  had a significantly higher PER than the rest of experimental groups. Many studies demonstrated the result of a protein sparing effect of lipid (Oliva-Teles, 2001, 2002; Boujared et al., 2004).

There were a strong relationship (r =0.96) between the dietary lipid levels and the lipid in the liver (Table 4). This agrees with many other studies that have shown that dietary lipid levels correlate strongly with liver lipid content (Nanton et al., 2001).

In all experimental groups, liver weight, liver fat and hepatosomatic index increased significantly (P≤0.05) with increasing level of lipids from 10% to 16% .The accumulation of fat in liver of sea bass fingerlings fed diets containing 14 and 16% lipid suggests that white sea bass have a limited ability to metabolize lipids (Lopez et al., 2006).  The white sea bass my be similar to the Asian sea bass, which are known to accumulate excess lipid in the liver because they have only limited capacity to oxidize lipid as a source of metabolic energy (Williams et al., 2003). Survival was significantly higher for group of Sea bass fed diet containing 14% lipid than the rest of experimental groups.

 

 

Table 5. body composition (on wet weight basis)of sea bass fingerlings fed the experimental diets.

Means+ S.E.M. of triplicate groups.

Means in the same row sharing the same superscript are not significantly different (P≤0.05).

 

The effect of dietary lipid levels on body composition is presented in table 5. Dietary lipid level had no significant effect (P≤0.05) on moisture, lipid, protein and ash content. In agreement with Lopez et al. ( 2006).

 

Calculation of the economical efficiency of the tested diets was based on the costs of feed because the other costs were equal for all studied treatments. As described in Table (6) feed costs (L.E) were the highest for the 16% level of lipid diet and gradually decreased with decreasing the levels of lipids on the other diets. These results indicate that increasing lipid levels in sea bass diets reduced the feed cost/kg. However, the relative cost to the lowest lipid level 10% was 90, 78 and 89 for lipid levels 12, 14 and 16% respectively. It was found that lipid level 14% in the diet of fingerlings sea bass seemed economic than the rest of experimental groups. The reduction of feed cost was easily observed for the feed cost per Kg weight gain which decreased with increasing lipid level till 14% and increased at lipid level 16%. These results support the growth performance parameters of fingerlings sea bass fed diet containing 14% lipid (Table 3). This is very important for sailing fingerlings sea bass.

     

Table 6 Feed cost (L.E) for producing one Kg weight gain by Seabass fingerlings fed on the experimental diets

 

 

It could be concluded from the present investigation that Sea bass fingerlings require 14% dietary lipid for best growth performance.

 

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