Sweet potato (Ipomoea batatas) leaf meal as partial replacement for soyabean meal in catfish (Clarias gariepinus) juvenile diet

Irabor Arnold Ebuka, Obakanurhe Oghenebrorhie¹, Pierre Hardin Jnr², Adeleke Mosunmola Lydia³ and Chukwurah Ikechukwu Augustine⁴

Department of Fisheries and Aquaculture
¹ Department of Animal Production, Dennis Osadebay University, Anwai Asaba
Arnold.Irabor@dou.edu.ng
² Fisheries and Aquaculture Department, Kagoshima University, Japan
³ Department of Fisheries, Federal University of Technology, Akure
⁴ Department of Environmental Management and Toxicology, Faculty of Environmental Science

Abstract

The quest to reduce production cost in fish farming through the use of cheaper conventional materials has become paramount. Some agricultural underutilized products such as sweet potato leaves have the potential to substitute as plant protein source. However, only a few researches has been conducted in this regard. Catfish farming becomes more profitable with a significant cut down on feed cost. This study investigated the partial replacement of soyabean with sweet potato (Ipomoea batatas) leaf meal (SPLM) and the effects on growth, haematology, serum and carcass quality on juvenile Clarias gariepinus. Data collected were statistically analyzed using one-way Anova. Significant (p < 0.05) differences were observed in all parameters across diets. A progressive increase in mean values of growth parameters as inclusion levels of SPLM increased was recorded. However, 30% and 40% showed significant decrease. Considering mean weight gain, protein efficiency ratio, feed conversion ratio, specific growth rate and survival rate, the best performance was observed in 20%. Also, blood profile, serum and water quality parameters were optimum in 20%. A substitution of soyabean meal with 20% SPLM in fish diets is recommended for Clarias gariepinus juvenile.

Keywords: aquaculture, Clarias gariepinus, feed formulation, haematology, sweet potato

introduction

Aquaculture production in Nigeria despite its importance, face some challenges which include high cost of production, insufficient technical know-how, poor government policies, inadequate land and water supply, poor market and poaching (Adeleke et al 2020). These have led to inadequacy in the overall fish supply (only 55% of all fish consumed) (WorldFish, 2018). However, these shortfalls have been linked mainly to high finance involved in fish production due to cost of feed ingredients (estimated to about 65% production cost especially protein sources) (Okocha et al 2021; Irabor et al 2022a).

Soyabean meal has been widely depended on as plant protein source in fish feed formulation, however it is part of the scares and most expensive ingredients. To minimize this dependence, it is important to explore other cheap and available plant protein sources (Irabor et al 2022b) Some researchers have reported that plant leaves e.g., pigeon pea, moringa and pigweed are suitable protein sources capable of providing certain levels of required protein for optimum fish productivity (Nwachi and Irabor 2015; Irabor et al 2021a; Irabor et al 2022c) Though, plants differ in their nutritional potentials and bioactivities of phytochemicals present in them. Aside being economical and readily available, plant protein sources contain low nitrogen and phosphate which reduces the rate of pond water eutrophication.

Protein as the major nutrient required in the diets of Clarias gariepinus is used up for numerous functions such as rejuvenation of warn out tissues, metabolic activities and growth. Thus, the performance and wellbeing of C. gariepinus depends on the levels of available protein consumed (Irabor et al 2016; Irabor et al 2021b). Although, it is necessary to ensure a balance in the dietary protein as same way deficient in supply impair growth performance and health, excessive supply could also negatively affect the growth rate, increase nitrogenous waste and give rise to stress and diseases due to the increased presence of microbes.

Sweet potato (Ipomoea batatas) leaf has relatively high amount of protein, categorizing it among the cheap and readily available plant protein sources for animal diet. Few researchers have conducted studies to determine the nutritive value of sweet potato leaf (SPL). Luo et al (2020) reported the crude protein levels of SPLM to vary between 29.55-29.85%, high mineral profile and vitamins A, B, C and E. Aside the rich nutrient profile of SPL, the presences of anti-nutritional properties have been established as one of the factors affecting its utilization as feed for some animals (Abong et al 2021).According to Priyanka et al (2020) the invertase and protease inhibitors are cyanide, while tannins, oxalate and phytate are some of the properties present in the leaf. These could impair fish growth if not reduced or completely removed via appropriate processing such as room temperature drying and grinding before inclusion into fish diets.

Sweet potato leaf as a food source, also have medicinal uses due to its high therapeutic properties and this can also be exploited when fed to animals. Furthermore, the toxicity levels of an additive in fish diets could be evaluated through haematological study. This is paramount to ensure the wellbeing of the fish amidst production cost reduction (Obakanurhe and Akpodiete 2021).

The study investigated the performance of Clarias gariepinus juveniles fed diets with varying inclusions of sweet potato leaf meal as partial replacement for soyabean meal.

Materials and methods

Research location

This study was conducted at the Fisheries and Aquaculture Department, Federal University of Technology, Akure. The town Akure is situated in Akure South L G A of Ondo State, Nigeria. It lies on longitudes 5⁰ 18^’E and latitude 7⁰ 17^’N.

Procurement of feed ingredients/formulation of test diets

The procured ingredients for the study were protein sources (fish meal, soya beans meal and groundnut cake), energy source (maize and wheat bran), minerals (vitamin premix, lysine, methionine and salt) and binder (starch). They were all procured from the popular food stuff market in Akure (Shasha market) and were pulverized into fine mixture. Sweet potato leaves were harvested from the Agronomy Department farm of same University and were properly rinsed to eliminate filths before drying under room temperature to ensure retention of its green coloration and reduce the antinutritional factors. The dried leaves were crushed using hammer mill to approximately 3 mm leaf meal and added into the fine mixture at various inclusion levels (10%, 20%, 30% and 40%) respectively (Table1).

Using a multiple phase model pelletizer and dies (2 mm), concentrates were pelleted into sized feeds. To further reduce moisture and safely preserve feeds, the pellets were dried under ambient temperature (30 ^OC) then bagged and labelled properly.

Experimental fish and set up

Five hundred (500) juvenile C. gariepinus were procured from a notable hatchery in Akure. and transported in well aerated plastic bags to the Research Laboratory, Federal University of Technology, Akure. Aided by sensitive bean balance and calibrated meter rule, the initial body weight and length were measured. The average initial weight and length were 10.01 g and 8.18 cm respectively.

To avoid infection due to stress, fish samples were disinfected for 20 minutes using 2 ppm copper sulphate. Thereafter, stocked in a well aerated 4 m² concrete tank and fed 2 mm commercial feed (Ziglar) at 5% body weight twice daily (7:30 hrs. and 17:30 hrs.) for two weeks to help sample acclimatize properly.

A total of twenty tanks of 1.6 m² (3 x 3 x 0.6) were holding capacity was used for the study and twenty-five juveniles were stocked per tank. Each was labelled T1_a-d (control) without the test ingredient, while T2_a-d, T3_a-d, T4_a-d, and T5_a-d were administered varying levels of SPLM.

The sampled fish were cultured for a period of eight (8) weeks, August to October, 2022.

Data collection

The data collected to the barest minimum (0.1) on weekly basis were; body weight (g) and total length (cm)

Performance and Feed Consumption

Performance indices i.e., mean body weight gain, percentage live weight gain, feed intake, feed conversion ratio, protein efficiency ratio, specific growth rate and mortality rate were examined using, Irabor et al (2021) procedures.

Body Weight Gain

The difference was via subtraction of the initial body weight from final body weight of fish.

BWG= W₂ – W₁

Where W₂ = final body weight

W₁ = Initial body weight

Percentage live weight gain (PLWG):

The difference between final and initial weights divided by initial weight stated in percentage gave the PLWG

Feed Intake (FI):

The daily consumed feed per fish gives the feed intake which is further expressed as feed given divided by total number of fish stocked per treatment.

Fluid (blood and serum) extraction and examination

Blood extracted from sampled fish were examined to confirm the effects of the additive on blood profile (white blood cell (WBC), red blood cell (RBC), haemoglobin, mean corpuscular volume (HMCV), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH), and packed cell volume (PCV)), using the standard procedures of Anand et al (2020).

Serum extracted from the blood sample were exposed to biochemical study to assess serum enzymes (Aspartate aminotransferase (AST), Alkaline phosphatase (ALP) and Alanine aminotransferase (ALT)) using, Raibeemol and Chitra (2020) procedures.

Water quality monitoring

Proper records of the water quality parameters of each tank were carried out twice on daily basis 7:00 hrs. and 17:00 hrs. throughout the study period using the prescribed methods of Muna et al(2021).

Data analysis

The statistical tool used to analyze the data collected was Analysis of Variance (ANOVA) in a totally randomized approach, while Duncan Multiple Range Test (DMRT) was used to ascertain the similarities at a significant level of (p<0.05).

Results

Proximate composition

The result of the proximate composition of SPL was showed in Table 2. Dry matter, crude protein, ether extract, crude fibre, ash, NFE, metabolizable energy were 94.12%, 24.44%, 3.75%, 17.23%, 8.92%, 41.66% and 2648.66 Kcal, respectively.

The proximate composition of the diets presented in Table 3 showed highest values of CP (40.96%) on 20% inclusion level, while the lowest was recorded on 40% inclusion level (39.23%). SPLM 0% had highest values (5.09% and 9.89%) in CL and MC, whereas the lowest values (4.51% and 7.42%) were recorded on 40% and 10% inclusion levels respectively. The values for CF and TA were higher on 40% inclusion level (7.17% and 5.68%) respectively, however 0% inclusion level had the least values (3.87% and 4.94%) respectively.

Performance characteristics of C. gariepinus juvenile

The recorded performance and nutrients utilization parameters of C. gariepinus juveniles fed different inclusion levels of SPLM at week 8 (Table 4). The best values (34.22g, 374.20g, 2.66%, 8.56, 2.13 and 95%) were for MWG, PLWG, SGR, PER, FCR and SR respectively at 20% inclusion level. Other parameter such as FI were observed to have highest value (79.52g) respectively at 0% inclusion level while at 40% inclusion level, the least values across all parameters were observed. There were curvilinear responses real life weight gain and feed conversion with optimum values being reached at a level of 20% sweet potato leaf meal in the diet (Figures 1 and 2).

Figure 1. Effect on live weight gain of increasing levels of Sweet Potato leaf meal	Figure 2. Effect on feed conversion of increasing levels of Sweet Potato leaf meal in the diet

Carcass quality

At the end of the study, carcass of the fish was analyzed to ascertain the influence of the test ingredient on the carcass quality using proximate analysis according to AOAC (2015). The difference observed were significant (p<0.05) across diets Table 5. However, the mean values for moisture content, crude lipid, crude protein, crude fibre, total ash and NFE ranged between 6.21 – 6.59%, 5.29 – 6.02%, 60.27 – 61.65%, 0.06 – 0.09%, 5.94 – 6.36% and 19.49 – 21.06%, respectively.

Haematological parameters

The blood parameters of sampled fishes reported that PCV, RBC and Hb showed the lowest values 25.35, 1.74 and 7.76 at 40% inclusion level, while the highest values (28.05, 3.10 and 8.17) were observed at 10% inclusion level. The lowest WBC value (6.62) was recorded at 20% inclusion level while 30% inclusion level had the highest value (7.21). Although, a corresponding increase was observed across diets for all other parameters (LYMPH, MCHC, MCH and MCV) but a significant decline was observed in MCH at 40% inclusion level. However, the lowest values (54.02, 30.64, 28.71 and 87.33) were observed at 0% inclusion level while the highest values (68.11, 33.89 and 141) for LYMPH, MCHC and MCV were recorded at 40% inclusion level except MCH with highest value (46.21) at 30% inclusion level.

Serum analysis

The blood serum extracted from the fishes analyzed (Table 7). A significant (p<0.05) differences were observed across diets as there is a corresponding increase in the serum parameters as inclusion levels of SPLM increases. ALT, ALP and AST had highest values (12.91, 55.35 and 23.04) at 40% inclusion level, while the least values were observed at 0% inclusion level (10.79, 45.79 and 19.46), respectively.

Water quality

Significant (p<0.05) differences were observed in all physicochemical parameters across treatments (Table 8). The mean values of pH, DO, Temperature, Nitrate, Nitrite, Salinity, Ammonia and Total Alkalinity were within range 7.13 – 7.34, 6.08 – 6.27 mg/l, 30.3 – 27.3 ^oC, 2.78 – 2.84 mg/l, 0.04 – 0.05 mg/l, 24.79 – 25.39 mg/l, 0.07 – 0.08 mg/l and 152.21 – 153.98 mg/l, respectively.

Discussion

The proximate composition of test diets revealed significant (p < 0.05) difference in all examined parameters. This was attributed to the nutritive potential of the test ingredient (SPLM) and this corresponds with the results of Lochmann et al (2021) who revealed a high nutrients content in SPL in a study conducted on the freshness of fish subjected to extracts of sweet potato leaf. Also, increase major nutrients were observed as inclusion levels of moringa leaf meal increased in Oreochromis niloticus diets (Elabd et al 2019).

The performance indices showed that there were curvilinear responses real life weight gain and feed conversion with optimum values being reached at a level of 20% sweet potato leaf meal in the diet. This impressive performance was due to the rich nutrients and antioxidant nature of the test ingredient. This finding confirms that of Lim et al (2020), who reported high nutrient values in extracts from banana, ginger and sweet potato leaves. Though, a declining effect on the FI corresponding to increased inclusion levels as observed across diets. This could be attributed to nutrient alteration, palatability, efficiency and digestibility of the test diets as inclusion levels increased to 30% SPLM and above (Shaguft et al 2021). A similar trend was revealed as inclusion levels of SPLM appreciated in the diets of roho labeo (Manish et al 2020). Xuhui et al (2020) also recorded a significant decline in the performance of gibel carp fed above 30% MOLM in their diets. The reduction in performance could also be attributed to the age of harvest, processing and growth inhibitors (phylates, tannin and phenol) present in the test ingredient.

The carcass quality of the sampled fishes examined at the end of 8 weeks study revealed a decreasing significant (p < 0.05) difference across diets for CP and CL as inclusion levels increased. However, a progressive increase was observed as inclusion levels increased across diets for NFE, TA, CF and MC. These observed differences could be the resultant effect of the high fibre, moisture and NFE of SPLM. A similar finding was reported by Duodu et al (2020) where changes in growth parameters, serum and carcass quality of O. niloticus was attributed to the plant protein sources used in the feed formulation.

The significant (p < 0.05) difference observed in the blood indices as inclusion levels of SPLM increased revealed the antibiotic characteristics of SPLM. The antioxidant content in SPLM had significant (p < 0.05) effects on the PCV and RBC which revealed depreciating values corresponding with progressive inclusion levels up to 40% SPLM. This report is in consistent with Kakwi and Olusegun (2020) observation on reduced PCV and RBC values when Cyprinus carpio were fed varying constituents of Mucuna pruriens. Also, SPLM enhanced the WBC values (immune-stimulatory capability) in the present study. Same was revealed when sesbania leaf meal was fed to C. carpio (Anand et al 2020). Similar trend was also observed in LYMPH, MCH and MCV which might be associated with stress. The exposure of carbamazepine to C. carpio had significant (p < 0.05) effects on LYMPH, MCH and MCV values ( Rezaei et al 2020). In a feed trail where Dicentrarchus labrax was fed chitosan and garlic at varying inclusion levels, similar trend was recorded (Abdel-Tawwab et al 2020).Though, the observed changes in the blood parameters posed no adverse effects on the fishes.

The analyzed fluid extract of sampled fishes showed significant (p < 0.05) difference across diets which revealed the impact of SPLM on serum enzymes range. The corresponding increased of enzymes range as the inclusion levels of SPLM increased could imply high hepatoprotective and antioxidant ability of SPLM, thus minimizing liver rupture through fatty acid peroxidation. The same finding was reported by Xuhui et al (2020) where progressive increase was observed in serum enzyme indices of Carassius gibelio juvenile fed high levels of fermented MOLM additive.

The water qualities during the culture period were observed to fall within the approved standard for fish culture(Muna et al 2020). Although the progressive incline in temperature and decline in pH and DO was attributed to the presence of microorganisms. The high quantity of uneaten feed in the culture media which is due to poor appetite in fish sample could have increased the high microorganism. Similarly, the high temperature, low pH and DO levels could have resulted in poor growth rate in the fishes due to low appetite and stress (Islam et al 2020) In another study, stunted growth in Dicentrarchus labrax exposed to temperature above 30^o C for a month (Islam et al 2020). The observed incline temperature and decline pH and DO values as inclusion levels of SPLM increases could be as a result of high turbidity caused by uneaten feed. Although, a contrary finding was reported by Huong et al (2020) where increased growth rate in Chitala ornate was observed as temperature increased to 32^oC.

Conclusion

The study revealed an excellent performance of juvenile C. gariepinus and significant cut-down on the cost of production at 20% SPLM inclusion level. Also, the antioxidant properties of the included SPLM influenced the white blood cell positively thereby improving the health status of the fish sampled. Therefore, a recommended 20% substitution of soyabean meal with SPLM will help reduce the cost of feed, in turn increase profitability and sustainability of fish farming.

Acknowledgements

We wish to acknowledge the entire staff of the Department of Fisheries for their immeasurable support throughout the period of this work. Our sincere thanks also go to the laboratory technologist for the assistance given during the lab work.

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