Engormix/Aquaculture/Technical articles

Protein requirements of fingerlings grey mullet (mugil cephalus)

Published on: 3/9/2010
Author/s : Abd ElHamid Eid
The protein requirements of fingerlings grey mullet, Mugil cephalus with an initial body weight of 5.5 g on the average, were studied by using four diets containing 32, 36, 40 and 44% crude protein, and fed for 90 days. The best growth performance was obtained with 36% crude protein and carbohydrate 35%, followed by the diets containing 40, 44 and 32% crude protein respectively. Protein efficiency ratio was decreased with increasing dietary protein levels.
Body protein was increased with increasing dietary protein levels up to 44%. There were an inverse relationship between the body moisture and lipid content. From the economical point of view, the highest net return, return of investitment, production of pound and production of each gram  of diets  was in group of fish fed on the  diet containing 36% crude protein. In conclusion, the optimum protein level for grey mullet  (weighing 5.5 gram) was 36% crude protein.
Keywords: Protein, requirement, fingerlings  grey mullet


 The economic success of controlled production of fish depends mainly on the cost of feed and particularly on that of protein, as protein is the most expensive component in artificial diets of fish. Knowledge of the protein requirement  is essential in formulation of well-balance and low cost artificial diets (Papoutsologlou and Alexis (1986). The dietary protein requirements of several species of young fish have been reviewed (NRC, 1983; 1993, El-Dahhar, 2000a,b).
Although members of the mugilidae are widely distributed in Egypt and much attention has been given to their controlled mass production. However only a few studies on the formulation of suitable artificial diets have been reported (Albertini-berhaut, 1974, Papoutsoglou and Alexis, 1986). In spite of these studies, the picture is still not clear and the dietary protein requirements of grey mullet inadequate, so more studies are required. The present study was undertaken to determine the quantitative protein requirements of Mugill cephalus fingerlings.
Culture condition:
Three hundred and sixty fingerlings grey mullet were collected from a wild population weighing 5.5 gm on the average from Ashtom Elgamel Port-Said . They were randomly distributed in 12 circular tanks (200 liters) 25 fish in each in the lab. Sixty fish were taken and subject to proximate analysis by standard methods  (AOAC, 1980). The water temperature was maintained at 24 + 1oC by a 250-watt immersion heater with thermostats  in each tank. The salinity was 14 ppt. All tanks were continuously aerated by air pump. One third of water was changed every day . Fish were acclimatized to the experimental condition for two weeks prior to the experiment. The experimental period lasted for 90 days( from 22/12/2003 to 21/3/2004). All fish in each tank were weighed every 10 days. The temperature , Oxygen and salinity were measured daily by oxygen temperature meter (Metteler Toledo, model128.S/Noo 1242) and salinity meter. The pH and Ammonia  were measured every two days by pH meter (Orion model 720A, S/N00 13052) and Ammonia meter (Hanna ammonia meter). The average water quality criteria of all tanks are presented in Table 1.
Table 1. Average water quality criteria of experimental tanks used in the experiment.  
Temperature                                                   24+ 1 0C
Oxygen (mg/L)                                              5
Ammonia (NH3)                                            0.001
PH                                                                 7.00
Salinity (ppt)                                                  14.00
Diet and feeding regime:
The experiment was undertaken at Fish Research Lab at Elgamel, Port-Said. Four isocaloric diets containing 32, 36, 40.and 44% crude protein  were formulated  (Table 2). Dry ingredients were passed through screen (0.6mm diameter hole) before mixing into the diets. Mixtures were homogenized in a feed mixer model SNFGA (kitchen aid st. Joseph, M 149085 USA). Boiling water were then blended to the mixtures at the rate of 50% for pelleting. An autoclave was used to heat the diets for 20 min after adding boiling water using a maximum pressure of 1.2 kg/cm2G. Vitamins and minerals mixture and 4% exogenous zymogene were added to diet after heat treatments. The diets were pelleted using meat grinder of kitchen aid with a 1.5 mm diameter and kept frozen until they used.   The experimental diets were fed at rate 3% of tank fish biomass  per day. The daily amount of food was offered two times at 9.00 a.m and 3.00 p.m,  and the amount of diets were readjusted after each weighing. The experimental diets were analyzed for moisture, protein, ash, fat and fiber by standard methods (AOAC, 1990). The composition and proximate analysis of the diets are given in Table 2. The parameters chosen for the evaluation of the experimental diets were weight gain, Feed Conversion Ratio (FCR), Specific Growth Rate (SGR) and Feed Efficiency (FE).
Analytical Methods
At the end of the experiment, sample of 10 fish from each treatment were taken randomly within average weight and dried at 700C for 48-72 h and passed through a meat grinder into one composite homogenate per group. Content of homogenized fish was analyzed according to the methods of AOAC (1990).
Statistical Analysis
Statistical Analysis was carried out using MSTAT program version 4 (1987). Significant differences among the mean of different treatment were compared by using  by Duncan's multiple range test (Duncan, 1955). 
 The growth performance of fingerlings grey mullet fed different protein levels are shown in Table 3.  Diet 2 which contained 36% crude protein gave significantly (P<0.05) the highest weight gain, Specific growth rate (SGR),  protein efficiency ratio (PER) and  feed efficiency (FE) than the group of fish fed on  diets containing  40, 44 and 32% crude protein respectively. The best food conversion ratio (FCR) was recorded in group of fish fed diet containing 36% crude protein than the rest of experimental groups.
Final mean weight and SGR increased as the dietary protein level increased from 32 to 36% crude protein, and decrease at higher protein levels. This response to increasing protein levels is similar to that reported for grass carp (Dabrowski, 1977), eel (Nose and Arai, 1972) and tilapia (Jauncey, 1982) and conforms with the general pattern observed  for high quality proteins (Harper, 1965). Group receiving diet  containing 36% crude protein had also the highest  food consumption, a decrease being apparent for higher and lower protein levels, which in agreement with De Silva and Perera (1976) for M. cephalus. Average protein efficiency ratios (PER) values for the experimental diets are presented in Table 3. Generally PER decreased with increasing dietary crude protein level up to 44% as has been noted in O. mossambicus (Jauncey, 1982); O. niloticus (Siddiqui et al (1988 and Eid et al, 2003)) and other fish species (Ogino and Saito, 1970). The concentration of dietary protein had performed  effect on muscle composition of fish (Table 4). There was a significant (p<0.05) increase in muscle protein content with increasing dietary protein level. Similarly, fish fed high-protein diets tended to have lower muscle lipid content. Similar results concerning the effect  of dietary protein in carcass composition has been observed on other studies with common carp ( Zitter et al., 1984), plaice (Cowey et al., 1972), young grey mullet (Papoutsologlou., 1986) and Nile tilapia (Eid et al., 2003). The ash content was unaffected by different dietary protein levels, as has been reported with other fish species (Jauncey, 1982; Siddiqui et al., 1988 and Eid et al., 2003). There were an inverse relationship between the body moister and lipid content, in agreement with Jauncey, 1982 and Eid et al., 2003).
Table 2 composition and proximate analysis of  the  experimental diets.
Ingredient                                                  Protein level (%)
                                                               32           36           40           44
fish meal (70%)                                  26           33           34           40
Soybean meal (44%)                         23           23           32           34
Yellow corn                                         44           37           27           19
Fish oil                                                    2             2             2             2
Corn oil                                                  3             3             3             3
Mineral Mix.1                                       1             1             1             1
Vitamin mix. 1                                      1             1             1             1
Proximate analysis(%)
Moisture                                               7.30        7.40          7.70      8.80
Crude protein                                      32.20     36.50     40.30     44.60
Ether extract                                       9.30       9.50         9.30      9.40
Crude fiber                                          2.70       2.70       3.10       3.30
Ash                                                        7.30        8.20        8.80       7.70
NFE 2                                                   41.20     35.70     30.80     26.20
ME (Kcal/100g) 3                              364.4     366.3     364.6     366.0
P/E 4                                                     88.36     99.64     110.53   121.8
Cost of  kg (L.E)                                 3.54        3.93        4.14        4.50
1- Vitamin and mineral mixture / kg premix : Vitamin A , 4.8 million IU, D3, 0.8 million IU, E, 4g, K, 0.8 g, B1, 0.4 g , Riboflavin 1.6g, B6, 0.6g, B12 , 4 mg pantothinic acid , 4g, Nicotinic acid 8g, Folic acid , 0.4g
2. Nitrogen Free Extract.
3. Based on 4.5 kcal/g protein, 8.15 kcal/g fats and 3.49 kcal/g  (Jauncey and Ross, 1982).
4. milligram/kcal.
Table 3. Performance of grey mullet as affected by dietary protein level.
Parameters                                          Dietary Protein level (%)
                                               32                           36               40                       44
Initial weight (g)                  5.50                       5.60            5.60                    5.40
Final weight (g)                    41.7d                     68.8a        59.7b                  50.7c
Weight gain (g)                    36.2d                     63.2a        54.1b                  45.3c
SGR 1                                   2.26d                     2.81a        2.65b                  2.47c
Feed intake (g)                    94.21d                   113.76a   113.6b                104.19c
FCR 2                                   2.6a                       1.8d            2.1c                    2.3b
PER 3                                    1.19b     '              1.52a       1.18b                   0.97c
FE 4                                       0.38d                     0.56a       0.48b                   0.43c
Mortality (%)                       20.0a                     12.0c        16.0b                   16.0b
*. Means in the same row having the same letter are not significantly different (p<0.05).
  1. Specific Growth Rate (%/day)= Ln W2- Ln W1/Time (days)X100
  2. Feed Conversion Ratio= Feed intake (g)/wet weight gain.
  3. Protein Efficiency Ratio= wet weight gain/ protein intake.
  4. Feed Efficiency Ratio= wet weight gain/ dry wt feed offered.
Economic Efficiency:
Table 5, Shows the results of economical evaluation including the costs and income.
Total cost were found to be 32.0, 34.83, 34.88 and 34.84 L.E for the groups of fish received diets containing 32, 36, 40 and 44% crude protein respectively. These  results revealed that the total costs of  40% crude protein were higher 34.88 L.E than the other groups. On the other hand, the  total costs of  32% crude protein were lowest
32.00 L.E due to the cost of feed ingredient. Net return in L.E were  8.00, 31.17, 17.62 and 17.66 L.E  for the group of fish received diets containing 32, 36, 40 and 44% crude protein respectively. Percentage of net return to total costs for treatment cited above were 25, 89, 50 and 51% respectively, indicating that the highest net return of investment were obtained with the group of fish received diet containing 36% crude protein. The productivity of each gram of diet were 0.38, 0.56, 0.48 and 0.43g for the groups of fish received diets containing 32, 36, 40 and 44% crude protein respectively. From the economical point of view, results suggest that the protein level of 36% for grey mullet weighing 5.5g is recommended to achieve the highest percentage of net returns to total costs. In conclusion , the optimum dietary protein level for grey mullet weighing 5.5g was 36%  crude protein.
Table 4. The effect of dietary protein levels on body composition (% wet weight) of Mugill cephalus.
Protein levels(%)                 Protein                   Fat                        Ash         Moisture
Initial                                    14.90                     7.80                       4.60        72. 70
32%                                       15.90a                   13.90d                   4.10a     66.10ab
36%                                       16.30b                   13.70c                   4.15a     68.85c
40%                                       16.60c                   13.30b                   4.16a     65.94a
44%                                       17.01d                   12.80a                   4.18a     66.01a
figures in the same column having the same superscript are not significantly different (P>0.05).
Table  5. Economic Efficiency (%) for grey mullet as affected by dietary protein levels for 90 days.
Treatments                                                                          Protein levels (%)
Costs and Returns                                                             32           36           40           44
Fingerlings (L.E) 1                                                              25.0        25.0        25.0        25.0
Feed (L.E) 2                                                                        7.0          9.83        9.88        9.84
Total 3                                                                                 32.0        34.83     34.88   34.84
Net return (L.E) 4                                                               8.00        31.17     17.62 17.66
Return of investment (L.E) 5 (%)                                   25.00     89.00     50.00 51.00
Productivity of one pound (kg/L.E) 6                            0.022     0.040     0.033 0.027
Productivity of one gm of diet (gm) 7                           0.38        0.56        0.48   0.43
  • 1. Price of fingerlings (L.E) = price X numbers.
  • 2. costs of feeds (L.E) = No. of kg feed X price of Kg
  • 3. Total Cost (L.E) = Price of fingerlings + costs of feed
  • 4. Net return (L.E) = Return - Total costs
  • 5. Return of investment (L.E)= net return/total cost
  • 6. Productivity of one pound (kg/L.E)= weight gain/total cost
  • 7. Productivity of one gm of diet (gm) = weight gain / amount of feed consumed
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