Pakistan, due to the lack of resources in the production rate is low intensive agriculture. Therefore, introducing the cheap energy source i.e. carbohydrates, the production rate can be improved. Fish fauna is rich in Pakistan, but in warm-water fish, only seven species and in cold water fish only two species are grown on commercial level.
Carbohydrates are considered energy cheaper food for the animals, but the ability of fish to digest carbohydrates in the diet has been reported to the difference between different species. This difference can be explained by the different activities of endogenous carbohydrate digestive different fish. However, carps can utilize high level of carbohydrates in the diet. Similarly, carnivorous fish are poorly able to utilize carbohydrates rather than herbivorous and omnivorous fish, but it is well known that the tents were reported to be in better utilization of carbohydrates, because of their omnivorous or herbivorous diet.
Rohu, one of three carp (IMC) and an omnivorous fish, has the ability to use carbohydrates to 43% in the diet without adverse health effects. This study aimed to determine the acceptance of corn as the main source of carbohydrates and make a comparison of important aspects of fish metabolism of L. rohita fed corn feed (G/NG) at three protein levels i.e. 30%, 35% and 40% in practical and economic systems for commercially available species of carp i.e. Labeo rohita. These new formulations minimize the cost of fish and reduce the waste produced by the fish.
The semi-crystalline nature of starch granules, as detected by X-ray diffraction studies, consists mainly of short amylopectin chains which form double helices associated into clusters forming crystalline lamellae. Recent reports showed that the crystallinity decreased with increasing amylose content in corn starches. However the precise role played by the amylose in the structure of starch granule is still unclear. Apart from the influence of amylose content on gelatinization, gelatinization temperatures and/or enthalpy increase with the crystallinity. This holds for waxy starches of different botanical origin as well as for low and high amylose corn starches.
Materials and Methods
The basic feed ingredient i.e. corn was procured and ground to make powder which were added approximately 80% of water (v/w) and autoclaved at 15 psi for one hour to obtain maximum gelatinization. These gelatinized corn ingredients were spread over a tray and dried in oven at 60°C. The dried mass was then pulverized through a hammer mill with 0.5 mm screen. Protein source was gelatin and fat free casein, while lipid source was sunflower oil and cod liver oil and carbohydrate source was corn (G or NG).
Chromic oxide was added as an indigestible marker. All these ingredients (Table 1) were ground and sieved to incorporate into diets and mixed well for 30 minutes, then fish oil was slowly added, while mixing thoroughly. Then the dough was given steam for 5 min in an autoclave. Vitamin-mineral premix was added after cooling the dough and then pellets of 2 mm were made by hand pelletizer. The pellets were dried in a drying oven for 48 hours and stored until use. Three different crude protein levels (30%, 35% and 40%) were used to formulate six semi purified diets (T1: G, 30% CP; T2: NG, 30% CP; T3: G, 35% CP; T4: NG, 35% CP; T5: G, 40% CP and T6: NG, 40% CP) with either gelatinized or non-gelatinized corn starch.
Experimental design and feeding protocol
Labeo rohita fingerlings purchased from government fish seed hatchery, Satiana road, Faisalabad were allowed to acclimate at ambient conditions fed on control diet (NG, 30% CP) for one week before initiating the trial. After acclimatization, fingerlings were transferred randomly into glass aquaria [90L×30W×45H (cm) with 29 L water capacities each]. For each treatment there were two replicates and in each replica forty fingerlings were stocked. Fish were given test diets at the rate of 4% live wet body weight twice a day (morning and afternoon) in the feeding aquarium.
Representative samples of six experimental diets and dried samples of feces of every replica were homogenized separately in a mortar pestle and chemically analyzed by AOAC protocols : oven drying at 105°C for dry matter (DM); microkjeldahl analysis for crude protein, chloroform methanol extraction method  for crude fat through 10454 soxtec system HTz, electric furnace for ash. Chromic oxide (Cr2O3) was estimated in dried feed and feces according to Divakaran  through UV/VIS2001 spectrophotometer.
The digestibility of nutrients is not defined precisely in many commercial feeds and it is shown that feed performance and digestibility can be increased with the use of extrusion technology . Present study is comparing the digestibility of gelatinized and non-gelatinized corn feed at various protein levels. Apparent nutrient digestibility coefficient (%) of test diets is shown in Table 2.
% Degree of Gelatinization (%DG)
The % degree of gelatinization in the temperature range of 50-95°C was followed by the spectrophotometric method based on the formation of amylose-iodine complex. In fact, %DG based on measurement of absorption peak at 600 nm can be taken as the ratio of solubilized amylose sites to the total amylose sites available in raw starch. Taking this point into account, a comparison was made between the curves in Figure 1. The % degree of solubilized amylose sites to the total in the raw starch was higher for corn starch, followed by Amioca. Although this ratio for Hylon VII was low at lower temperatures, it increased after 80°C. This corresponded to the point where the increase in %S of Hylon VII started on the solubility curve (Figure 2).
The apparent nutrient digestibility coefficient (ADC) of crude protein was maximum for the T2: NG, 30% CP (67.70 %) and this was followed by the T1: G, 30% CP (65.40%), T6: NG, 40% CP (52.60%), T5: G, 40% CP, T4: NG, 35% CP (40.00% and 32.60%) and T3: G, 35% CP (20.20%) (Table 3-7).
Digestibility describes the fraction of the nutrients of energy in the feedstuff that is not excreted in the feces. Digestibility is one of the most important aspects of evaluating the efficiency of feed stuffs. Yengkokpam reported that increased gelatinization decreased the dry matter digestibility. Similar trend was observed in the present study as non-gelatinized T6: NG, 40% CP showed the maximum digestibility. This also showed that protein levels has no effect on carbohydrate digestibility as reported by Misra 28% and 35% CP levels showed non-significant variations among G/NG corn. Our results indicates that maximum ash consumption occurs in non-gelatinized corn at 35% protein level in fish same as reported by Kumar, Singh, Mohanta that 35% protein level observed to be the optimum for contents of ash retention.
Sethuramalingam and Haniffa reported high lipid digestibility at 35% protein level while Yengkokpam reported fat digestibility affected by increasing level of gelatinization in corn. On contrary, present study indicates the lipid digestibility better at 40% protein level in non-gelatinized corn test diet comparing all other in L. rohita. These results also indicated that fat digestibility affected by different protein levels as reported by Misra, both G/ NG corn showed non-significant variations with reference to different protein levels. Yengkokpam reported the maximum protein digestibility at gelatinized 40% protein level in L. rohita while NG, 30% CP diet produced better protein digestibility, nutrient utilization and energy compared to other, as proper balance between dietary protein and energy is important for optimum growth. Less energy of rohu fingerlings fed low protein (30%) reported.
Total energy and carbohydrate digestibility were found 80% in fish fed NG, 35% CP [11. On contrary, results from present study indicate the maximum total digestible energy in test diet with non-gelatinized 40% protein level, which means that gelatinization, affected the rate of digestibility in L. rohita in every aspect i.e. dry matter, ash, lipid, protein and gross energy while 40% protein level proves suitable in dry matter, lipid and total energy digestibility while 30% for protein digestibility in L. rohita which is in agreement with Kumar; Mohapatra  (Figures 3-7).
It may, therefore, be concluded that non-gelatinized corn at 40% protein level proved as a promising fish feed ingredient being more efficiently utilized and gave better growth, digestibility and tissue deposition results in Labeo rohita. The palatability of non-gelatinized corn and its excellent nutritional value including high level of protein and relatively high nutritional digestibility, proved to be a high quality ingredient for this fish. The results of present study could be useful as starting point for formulating cost effective, nutritionally balanced fish diets by sparing protein with carbohydrate sources.
Since gelatinization is a diffusion controlled reaction, both the swelling and solubility outcome as important parameters among the factors affecting the extent of gelatinization. In gelatinization of normal corn starch, both processes seemed to be effective, while in the case of Hylon VII the solubilization of starch controlled the process. Another important point to be noted is that free amylose rather than the total in starch affected the gelatinization.
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