Effect of processing methods on the utilization of cassava (Manihot esculenta Crantz) leaf meal (CLM) by African catfish (Clarias gariepinus)

I U Udo and J F John

Department of Fisheries and Aquatic Environmental Management, University of Uyo, Uyo, P.M.B. 1017, Uyo-Nigeria
dorime_2004@yahoo.com

Abstract

Cassava (Manihot esculenta) is available everywhere around the globe and the leaves are left wasted after harvest. Despite its high nutrient profile, incorporation in fish diet is hindered by its high cyanogen content. Processing could help remove the cyanogen and enhance its utilization by fish. The effect of processing methods on the utilization of CLM by African catfish (Clarias gariepinus) was therefore tested. The aim was to determine the processing method that will give the best performance in terms of growth, survival, health and feed utilization. Five isocaloric (19.32 kJ g^-1) and isonitrogenous (400 g kg^-1 diet CP) diets were formulated. Control contained no CLM. Diets 2 – 5 contained 200 g kg^-1 diet each of immersed + immersed (IMM+IMM), shredded + sundried (SHD+SND), pounded + washed (POD+WSH) and steamed + sundried (STM+SND) CLM respectively.  The five diets were fed to African catfish (C. gariepinus) juveniles in triplicate for 126 days.

Growth performance and feed utilization were greater in fish fed diet IMM+IMM followed by POD+WSH. No health hazard was detected in all the diets. In this study, we demonstrated that immersing+immersing was the best processing method that enhanced efficient utilization of CLM by C. gariepinus followed by pounding+washing.

Keywords: Cyanide, immersion, pounding, steaming, sun-drying, washing

Introduction

Globally, aquaculture is growing in a very fast rate and more people than ever before are relying on fisheries and aquaculture for food and as a source of income. According to FAO (2014) global fisheries and aquaculture production totalled 158 million tonnes in 2012 - around 10 million tonnes more than 2010. Global trade in seafood tends to flow heavily from developing to developed countries. At present 38 per cent of all fish produced in the world is exported and in value terms, over two thirds of fishery exports by developing countries are directed to developed countries. The “Fish to 2030” report (World Bank 2013) finds that a major and growing market for fish is coming from China which is projected to account for 38 per cent of global consumption of food fish by 2030. China and many other nations are increasing their investments in aquaculture to help meet this growing demand. The same report has it that, aquaculture is expected to produce 62 per cent of food fish by 2030 with the fastest supply growth likely to come from tilapia, carp, and catfish. Sub-Saharan Africa, is expected to see a per capita fish consumption decline of 1 per cent per year from 2010 to 2030 but, due to rapid population growth of 2.3 per cent in the same period, the region’s total fish consumption will grow by 30 per cent overall.

However, soaring cost of feed is observed as one of the problems hampering the development of aquaculture in Nigeria (Gabriel et al 2007). This is as a result of high crude protein content (35-50%) which is the most critical and/or costly ingredient in catfish feeds where protein sources represent about 60 per cent or most of the cost of fish feeds. The primary source of protein in fish feed is fishmeal which is facing much pressure from both livestock and aquaculture industry. This has motivated the search for local, cheap and available ingredients that are unsuitable for direct human consumption as alternative protein source in practical diets for Clarias gariepinus. Leaf meal proteins are among the unconventional sources of protein that may reduce the high cost of fish feed (Udo and Umoren 2011). A particular leaf meal of interest as a potential dietary protein is cassava (Manihot esculenta).

Cassava (M. esculenta) leaves a by-product of cassava root harvest is (depending on the varieties) rich in protein (14-40% dry matter), mineral, vitamin B₁, B₂, C and carotenes (Adewusi and Bradbury 1993). The inclusion of leaf meal in aquaculture feed is fast gaining global attention over the years because of its available protein, mineral and vitamin contents and economic feasibility (Tacon 1997; El-Sayed 1999; Ali et al 2003). The major drawback to the widespread use of cassava leaves as food is “cyanide scare” as its content of cyanogenic glucosides could, depending on the variety be six times higher than in the roots. Apart from cyanide and tannin, possibly phytin limit the nutritional value of cassava leaves (Reddy et al 1982). There is risk of acute cyanide intoxication and death. Chronic exposure to sub-lethal level increases the incidence of goiter, tropical neuropathy and glucose intolerance (Oshuntokun 1972; Akanji and Famuyiwa 1993).

Different processing methods have been developed to detoxify cyanide from cassava leaf (Fasuyi 2005; Bradbury and Denton 2010), but their suitability in aquaculture has not been evaluated. This study seeks to assess the effect of four processing methods of cassava leaves on growth performance, survival, feed utilization and haematological parameters of C. gariepinus juvenile.

Materials and Methods

Experimental site

The 126 days experiment was carried out in the University of Uyo fish farm between October and February 2014. Fifteen aquarium tanks measuring 96x50x29cm³ were used. Each tank has a water holding capacity of 50 liters but water was maintained at the 20 liters levels throughout the study (Eyo 1994).

Collection and processing of ingredients

Samples of the M. esculenta leaf were collected from local farms in Uyo, Akwa Ibom State and subjected to the following processing techniques:

Steaming and sun-drying (STM + SND): The leaf samples was spread over a wire gauze placed on top of a boiling water for 30 minutes; the steamed leaf sample was further sundried for 2-3 days with adequate turning over to avert fungal growth (Fasuyi 2005).

Shredding and sun-drying (SHD + SND): Moulinex blender was used to cut the leaves into fine pieces; the machines blended samples were now sun-dried for 2 – 3 days with adequate turning to avert mouldiness till the processed samples were packed into tightly sealed nylon bags and analysis commenced immediately with minimum delay to forestall a further change in quality of samples (Fasuyi 2005).

Pounding and washing (POD + WSH): The leaves were pounded in a pestle and mortar for 10 min until the leaves were well macerated. This was followed by washing the pounded leaves twice in twice their weight of water at ambient temperature (Bradbury and Denton 2010).

Immersion and immersion (IMM + IMM): The leaves were immersed in ten times their weight of water at 50±3 °C for 2 hours followed by one change of water and further immersion for 2 hours at 50 °C (Bradbury and Denton 2010).

Other feed ingredients viz. wheat bran, fishmeal, soybean meal and white maize were sundried and ground individually to a fine powder by using hammer mill machine.

Chemical analysis

Proximate composition of the cassava leaf meal used in this study was analyzed. Dry matter (DM), crude protein (CP), crude fibre (CF), ether extract (EE), ash were analyzed according to standard methods of AOAC (1999). Phosphorus content of the triple acid digested extract was determined by the phosphovanado-molybdate (yellow) method. Calcium was determined using a Perkin-Elmer Model 5000 atomic absorption extract spectrophotometer (AOAC 1999). these were used to formulate the experimental diets while the proximate composition of other ingredients used was adapted from standard tables (ADCP 1983; NRC 2011).

Fish diet formulation and milling

Five isocaloric and isonitrogenous diets were prepared to contain 200 g kg^-1 diet (Bichi and Ahmad 2010) cassava leaves meal (CLM) that was processed using different processing techniques. The Control diet contained no CLM while the test diets contained Immersed-immersed (IMM + IMM), Shredded-Sundried (SHD + SND), Pounded-washed (POD + WSH) and Steamed-sundried (STM + SND) CLM respectively. Diet formulation was done using linear programming techniques (WINFEED 2.8). The formulated diet and proximate analysis of the diets are presented on table 1. Ingredients were then individually weighed using Camry balance (Emperors, China) and properly mixed together with adequate addition of boiled water to ensure smooth pelleting. Two per cent of cassava starch was used to bind the diet.

Pelleting was done using hand pelletizer. The strands were cut into short pieces and sun-dried for 3 days to remove moisture. The pelleted diets were then packed in water impermeable bags (Nylon bags) and kept in freezer until use.

Experimental procedures

Experimental fish were obtained from Safe Food fish farm Uyo, Akwa Ibom State, Nigeria. The fish were acclimatized for seven days in a rubber tank when they were fed ad libitum with diet of 450 g kg^-1 diet CP. They were then starved for 24 hours prior to being placed on experimented diets in order to empty their stomach and prepare their appetite for the new feed. The mean initial body weight of the fish taken with weighing balance to the nearest gram was 8.22±0.09 g. One hundred and sixty five fingerlings of C. gariepinus were randomly distributed into tanks representing five treatments and three replicates, at 11 fish tank^-1. The five different diets formulated were fed thrice daily at 5% of their fresh body weights, between the hours of 8, 13 and 18. Tanks were inspected daily to remove dead fish, if any. Morning and afternoon temperature and dissolved oxygen were monitored in-situ using DO meter, (HANNA, Romania, Europe). Total ammonia and pH were measured using commercial kits (Tetra Test, Tetra) once per week. A natural photoperiod was maintained during this stage (12 L: 12 D, based on average intervals from sunrise to sunset from October 2013 to February 2014. Aeration and continuous water renewal were maintained throughout the experiment. Unconsumed food particles were siphoned, dried and measured with the balance to determine their weight. The weight of the experimental fish and their controls were measured bi-weekly for the determination of their growth performance.

Estimation of growth performance, feed utilization and survival parameters

The overall growth parameter and feed efficiency indexes were computed using the following equations (i) weight gain (%) = (final weight – initial weight) x (final weight) ^-1 x 100; (ii) daily weight gain (DWG) = (final weight – initial weight) x t^-1; (iii) feed conversion ratio (FCR) = (dry food fed) x (wet weight gain ) ^-1; (iv) specific growth rate (SGR; % day ^-1) = [Ln (final weight) – Ln (initial weight)] x (number of days)^-1 x 100 and (v) survival rate (SR; %) = (Total number of fish sampled) x (Total number of fish stocked)^-1 x 100.

Haematological analysis

At the end of the experiment, about 0.50 ml of blood was collected from fish anaesthetized by MS-222 (Sandoz, Basel, Switzerland). Fish were cut at the caudal peduncle and blood was collected in coded 1.50 ml heparinized plastic tubes, stored in ice and centrifuge within 30 minutes of collection. The blood samples were analyzed at the Chemistry Department University of Uyo within 2 hours of collection. The Packed Cell Volume (PCV) of each blood samples were determined using haematocrit reader method (Dacie and Lewis 2001). The Haemoglobin concentration (Hb) of each blood sample was determined. The Red Blood Cell (RBC) and White Blood Cell (WBC) count of each of the blood sample each also determined. The absolute erythrocyte indices (MCH, MCV and MCHC) were calculated as follows: Mean cell haemoglotan (MCH pg) = (Haemoglobin x Red Blood Cell)^-1 x 10; Mean cell volume (MCV fl) = (Packed Cell Volume x Red Blood Cell)^-1 x 10; Mean cell haemoglobin concentration (MCHC %) = Haemoglobin x Packed Cell Volume)^-1 x 100.

Statistical analysis

Data were analysed as a design using the IBM SPSS statistics 19. Mean and one-way analysis of variance was performed to compare means. Duncan multiple range test was used to identify significant differences among different treatment means; P<0.05 was considered to be statistically significant.

Results

Water quality

The mean values for the physico-chemical parameters in the experimental tanks were 23.6±0.2 and 28.0±3°C, 6.20±0.02, 4.20±0.02 mg l^-1 and 0.03±0.01 mg l^-1 for morning and afternoon temperature, pH, dissolved oxygen and total ammonia respectively.   

Proximate composition of experimental diets and cassava leaves

The CLM used in the experiment contained 913 g kg^-1 Dry Matter, 276 g kg^-1 DM of crude protein, 126 g kg^-1 DM of crude fibre, 61.2 g kg^-1 DM of lipid and 75.0 g kg^-1 DM of ash while phosphorus and calcium were 6.00 and 21.5 g kg^-1 DM respectively. The proximate composition of the experimental diets is presented in Table 1. Nutrients for the formulated diets were all within the requirements by African catfish according to NRC (2011).

Growth Performance, feed utilization indices and survival of C. gariepinus fed the experimental diets.

Growth performance and feed utilization indices examined in this experiment are presented in table 2. The final mean weight was significantly greater in fish fed diet POD+WSH and IMM+IMM than in those fed the control diet and STM+SND while that of those fed diet SHD+SND was significantly greater than those on the control diet and STM+SND but lower than those on diets POD+WSH and IMM+IMM. The greatest weight gain was obtained in fish fed diet IMM+IMM followed by fish fed diet POD+WSH. The least gain in weight was obtained in fish fed diet STM+SND followed by the control diet. Average daily weight gain otherwise known as Growth rate (GR) and Specific growth rate (SGR) also followed the same trend.

There was a tendency for IMM+IMM, POD+WSH and SHD+SND to be greater than STM+SND and the control diet (p=0.682). Feed conversion ratio (FCR) was significantly greater in diets POD+WSH and STM+SND and protein efficiency ratio (PER) was significantly greater in diet POD+WSH than in other diets. This was closely followed by fish fed IMM+IMM which was significantly higher than fish fed the control diet and STM+SND. Fish fed diets POD+WSH and IMM+IMM also had higher survival rate as compared to others.

The growth trend showed good appetite to all the treatment diets, attested to by the increase in body weight (figure 1). However, growth rate was faster in fish fed diets IMM+IMM and POD+WSH from the third sampling date to the conclusion of the experiment.

Haematological response of C. gariepinus fed different processed cassava leaf meal

The mean values of haematological analysis of the blood of C. gariepinus are presented in Table 3. The result showed that IMM+IMM CLM based diet had significantly higher haemoglobin (Hb) level than the SHD+SND and POD+WSH which were significantly higher than STM+SND, SHD+SND CLM based diets and the control diet. The result obtained for red blood cell (RBC) revealed that diet POD+WSH and IMM+IMM had values that are significantly greater than others and the control diet which was not significantly different from the initial value.

The results obtained for the white blood cell (WBC) showed that SHD+SND was significantly greater than other diets, the control diet and the initial values. There was no significant difference in lymphocyte count among the different treatment mean. The packed cell volume (PCV) result showed that fishes fed SHD+SND, POD+WSH and STM+SND CLM based diets had increase in the PCV which was significantly different from the fish that were fed with the control and other diets which were not different from the initial values. Fish fed the control diet, IMM+IMM and SHD+SND CLM based diet had values for MCH significantly greater than POD+WSH and STM+SND but not significantly different from the initial value.  The values for MCHC were significantly greater in fish fed IMM+IMM, SHD+SND, POD+WSH CLM based diets than the STM+SND based diet, the control diet and the initial value.

Discussion

The physico-chemical parameters of the water in the experimental tanks fall within the optimal ranges for optimum fish production (Anyanwu et al 2012). Cassava leaves are rich in protein, calcium, iron and vitamins, comparing favourably with other green vegetables generally regarded as good protein sources. The amino acid composition of cassava leaves shows that, except for methionine, the essential amino acid values in cassava exceed those of the FAO reference protein (Lancaster and Brooks 1983). The total essential amino acid content for cassava leaf protein is similar to that found in hen's egg and is greater than that in oat and rice grain, soybean seed, and spinach leaf (Yeoh and Chew 1976). While the vitamin content of the leaves is high, the processing techniques for preparing the leaves for consumption can lead to huge losses. For example, the prolonged boiling involved in making African soups or stews, results in considerable loss of vitamin C.

The proximate composition of M. esculenta leaf meal in the present study collaborates with a priori findings of Fasuyi (2005) and Sutriana (2007). The similarities in chemical composition with the other study may be an indication that environmental factors such as season, geographical location and stage of maturity play a minor role in determining nutritive value of M. esculenta leaf meal. Further, values of chemical composition were comparable with those reported in other leaf meals such as Moringa oleifera (Dienye and Olumuji 2014), Leucaena leucocephala, and Ipomoea batatas (Sotolu 2010; Adewole 2008). This shows that M. esculenta leaf meal has the potentials to supply some of the needed nutrients in aquafeed.

The result of this experiment shows that higher mean weight gain and specific growth rate was achieved by diet containing immersed-immersed and pounded-washed CLM based diet as compared to the control diet and other diets. However, diet containing shredded-sundried CLM was superior to both the control diet and steamed-sundried CLM based diet. The superiority of shredded-sundried CLM over steamed-sundried CLM agrees with the findings of Fasuyi (2005) who reported that shredded-sundried CLM retained the least amount of cyanogen (i.e. 3.7 and 4.1% HCN retention respectively), tannin (62 - 64%). It also retained phytin to about the same extent (41- 42%). However, Bradbury and Denton (2011) found that cyanogen retained by immersed-immersed and pounded-washed CLM is higher (7 and 8% respectively) as compared to shredded-sundried CLM. The superiority of diets IMM+IMM and POD+WSH over SHD+SND might be an indication that key nutrients which are necessary to detoxify ingested cyanide were still available and best converted to flesh by the fish. The fact that feed conversion ratio was significantly better in diets POD+WSH and STM+SND than other diets is a clear indication that pounding and cooking can increase the ability of the feed being well utilized by fish. The values for FCR agree with the range of 2.23-2.9 reported by Ekanem et al (2010) for Heteroclarias. The PER is also in line with findings of Sutriana (2007) who recorded 0.74-1.88 for C. gariepinus fry though 30 CP diet was used and the fish fed at 7% body weight. The present study shows that shredding + sundrying is not a bad processing technique as compared to steaming + sundrying when using CLM in aquafeed. The findings are in agreement with earlier observations (Aletor 1993b; Bokanga 1994; Nambisan 1994; Fasuyi 2005) that the residual cyanide level in processed cassava products, depends largely on the nature and duration of the processing technique. However, the superiority of pounding + washing and immersing + immersing method agrees with the findings of Bradbury & Denton (2011) that preparation of CLM need a mild method that will not only remove the cyanogen but also retained the available nutrients. The poor performance of diets STM+SND and SHD+SND may therefore be ascribed to denaturation of linamarase activity at temperatures above 55^oC (Mkpong et al 1990). This point is further buttressed by the high survival rate of fish recorded in fish fed diet IMM+IMM as compared to others.

Haematological parameters are used in monitoring feed toxicity especially with feed constituents that affect the formation of blood in culture fisheries (Oyawoye and Ogunkunle 1998). Blaxhall and Daisley (1973) reported the essence of using haematocrit to detect anaemic condition in fishes. All the haematological parameters measured in this study were within the recommended physiological ranges reported for C. gariepinus. For instance, Wedemeyer and Yasutake (1977) recommended a range of 0. 77 - 1.58 (10⁶ mm^-3) for RBC, 5.4 - 9.3 (g 100 ml^-1) for haemoglobin, and 24 – 43% for PCV (haematocrit). Later on, Bhaskar and Rao (1989) recommended the following ranges for a normal healthy fish - 2.3 (1.7 - 4) 10⁶ min^-1 for RBC, 43 (22 – 48) % for PCV (haematocrit), 7.5 (5- 15) g 100 ml^-1 for Hb and 17.2 (10.9 - 38.1 %) for MCHC. Osuigwe et al (2005) observed changes in some haematological parameters of juvenile hybrid catfish (Heterobranchus longifilis x Clarias gariepinus) fed raw and 60 min-boiled jackbean seed meal (JBSM) at different dietary levels for 56 days. The haematocrit (packed cell volume, PCV), red blood cell (RBC) count, white blood cell (WBC) count and haemoglobin (Hb) concentration decreased significantly (P<0.05) with increasing dietary JBSM level. Though the mean values of the blood parameters of fish fed diets containing boiled JBSM (PCV = 29.9%; RBC = 1.2 x 10⁶ mm^-3; WBC = 15.9 x 10³ mm^-3; Hb = 8.31 g 100 ml^-1) showed significant improvement when compared with those fed raw JBSM diets (PCV = 28.68%; RBC = 1.13 x 10⁶ mm^-3; WBC = 14.63 x 10³ mm^-3; Hb = 8.31 g 100 ml^-1) they were, however, lower and  different (P<0.05) from those fed the control diet (PCV = 35.5%; RBC = 1.43 x 10⁶ mm^-3; WBC = 20.42 x 10³ mm^-3; Hb = 10.62 g 100 ml^-1). However, the observed reduction of the blood parameters did not go below the normal range of values recorded for catfish. This also agrees with the findings in this study. Some changes were recorded in this study based on the efficiency of the processing method. However, the slight fluctuation in the haematological parameters was not significant enough to affect fish health negatively.

Conclusion

• The data obtained from this study revealed that the growth rate of catfish  fed diets containing cassava leaves was improved when the leaves were subjected to double immersion in water prior to feeding.

  
  

• Feed utilization was also improved by using this processing method.

  
  

• There were no negative effects on fish survival by inclusion of cassava leaves in the diet.

  
  

• Fish health was not negatively affected by cassava leaf inclusion and processing method in any of the treatments.

Acknowledgement

The authors are grateful to the Directors, Processing and hatchery unit of the Department of Fisheries and Aquatic Environmental Management, University of Uyo, Uyo for providing facilities to carry out this work.

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Received 15 April 2015; Accepted 22 April 2015; Published 1 August 2015

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