Dietary Replacement Effects of Maize with Graded Levels of Melon Shell on Growth Performance of Clarias gariepinus Fingerlings (Burchell, 1822)

A 60-day study was conducted to investigate the dietary effect of replacement of maize with graded levels of melon shell meal (MSM) on growth performance of Clarias gariepinus fingerling. Five isonitrogenous diets were formulated. MSM was added to the diet to replace maize at graded levels; 0%, 25%, 50%, 75% and 100%. Total of 150 fish (3.40±0.05g) were randomly assigned to the five treatment diets. Each treatment contained 10 fish per tank and each treatment was triplicated in a completely randomised design (CRD). Fish were fed twice daily at 5% body weight in equal proportions. Results showed significant differences (P<0.05) for measured growth parameters. Fish fed diet containing 100% MSM had the highest mean weight gain (70.70±4.62g), specific growth rate (SGR) (5.06±0.10%), best feed conversion ratio (FCR) (0.54±0.04%) and protein efficiency ratio (PER) (1.68±0.11%) compared to other treatments and the control while fish fed 25% MSM had the poorest values for MWG (39.88±4.37g), SGR (4.20±0.16), FCR (0.60±0.02) and PER (0.95±0.11). MSM inclusion in diet of C. gariepinus up to 100% enhanced growth.


Introduction
The consumption and demand for fish as a cheap source of animal protein is increasing in Africa. In most countries, vast majority of the fish supply comes from the rivers as captured fisheries. FAO (2004) in "The State of the World Fisheries and Aquaculture" concluded that developments in world fisheries and aquaculture during recent years have continued to follow the trends that were already becoming apparent at the end of the 1990s, as capture fisheries production is stagnating and aquaculture output is expanding faster than any other animalbased food sector. Thus development policies increasingly perceive aquaculture as means for economic growth and prospect for future fish supply (FAO 2004). According to FAO (2006), fish supplies from capture fisheries can no longer meet the growing global demand for aquatic foods. Hence, there is a need for a viable alternative fish production system that can sufficiently meet this demand, and aquaculture fits exactly into this role. As aquaculture production becomes more intensive in Nigeria, fish feed will be a significant factor in increasing productivity and profitability (Akinrotimi et al. 2007). Jamiu and Ayinla (2003) opined that feed management determines the viability of aquaculture as it accounts for at least 60% of the cost of fish production.
Maize is one of the conventional feedstuffs, thus a major source of metabolisable energy in most compounded diets for catfish as it is readily digestible by fish (Olurin et al. 2006). FAO (2005) reported that maize, which is predominantly used for human consumption in Nigeria, is not provided in sufficient quantities. The use of maize in fish feeds is becoming increasingly unjustified in economic terms (Tewe 2004), because of the ever increasing cost. Therefore, there is a need to exploit cheaper energy sources to replace expensive cereals in fish feed formulation. For the purpose of nutritional and economic benefits, previous researchers have attempted to increase the use of non-conventional feed resources to replace conventional feed ingredients like maize and fishmeal in fish diet (Olatunde 1996;Baruah et al. 2003;Eyo 2005). To relieve the feed competition between man and animal and for profit maximization, melon shell appears to be very appropriate for this purpose.
Melon husks are shells that are discarded after processing or shelling of melon seeds (Citrullus vulgaris). Melon is a cucurbit crop belonging to the family cucurbitaceae (Abiodun and Adeleke 2010). Melon (seed) crops are grown, harvested and processed in large tonnage in Nasarawa Local Government Area of Nasarawa as well as Kaduna State, Nigeria. The seeds are removed from the fruit, washed, sun-dried and sold in large quantities (tonnage) annually for commercial purpose (as a special soup condiment). They are also used as domestic remedy for urinary tract infection, hepatic congestion, intestinal worms and abnormal blood pressure (Moerman 1998). The freshly shelled seeds were reported contained 34.24% crude protein, 45.95% fat, 7.18% crude fibre, 4.05% ash, 8.03% moisture and 0.56% carbonhydrate (Fagbohun et al. 2011). However, large quantities of the melon husks are discarded and burnt, which pollute the environment (Ogbe and George 2012). While the fisheries industry is threatened with acute shortage of conventional feed ingredients leading to low productivity, it may be possible to utilize melon husks as non-conventional source of feed ingredient for fish. The current study seeks to investigate the effect of varying dietary inclusion levels of MSM in replacement of maize on growth performance of C. gariepinus.

Materials and Methods
Experimental fish Fingerlings of C. gariepinus were procured from Regina Pacie fish farm in Abakaliki and transported to the Department of Fisheries and Aquaculture laboratory in a 50 litre and opened at the top within 20-30 minutes. Fish were subsequently subjected to a 2 min bath with 0.05% potassium permanganate (KMnO4) to prevent skin infections. The fish were acclimatized for two weeks in a tarpaulin tank (10m x10m x 2m) and fed ad libitum on a daily basis with commercial feed (Coppens International Helmond Netherlands) containing 45% crude protein.

Collection and processing of melon shell
Melon shells were collected from the rural women who process melon seeds for commercial purpose (also called "egusi" by the people); they were sundried (3-4 days) and milled to powdered form using manual grinding machine at Abakaliki main market to aid incorporation with other feed ingredient. The milled melon shell was incorporated directly with other finely ground feedstuffs, pelletized, sundried and individual diets were packed into separate bags and then stored in a cool and dry place.
The formulation was based on gross proximate composition of the ingredients.

Proximate Composition of MSM and Experimental diets
Samples of MSM and experimental diets were sent to the International Institute for Tropical Agriculture (IITA) Laboratories Ibadan. Samples were analysed chemically according to the official methods of analysis described A.O. A.C. (2000). All analysis was carried out in triplicate. Proximate composition of the MSM and experimental diets are presented in Table 2. Result showed that MSM has 14.88% CP, 7.16% moisture, 6.98% ash and 5.67% crude fibre.

Experimental design
A total of one hundred and fifty (150) fingerlings with an average weight 3.40±0.50 g were randomly assigned to fifteen experimental aquaria tanks (1m x 1m x 1m). Fish were subjected to five test diets with varying dietary inclusion levels of melon shell as treatments. Each treatment contained 10 fish and was triplicated in a completely randomised design (CRD). Fish were fed twice daily (9:00 am and 4:00pm) at 5% body weight for 60 days. Total fish weight in each tank was determined at two weeks intervals and the amount of diet was adjusted accordingly.

Water quality management
Water in the experimental tank was removed every three days and replaced with fresh water in order to prevent water fouling and also remove fish faecal waste. Physicochemical analysis of water was measured once a week during the study (Table 3). The following parameters were tested; water temperature, pH, and total dissolved solids (Turbidity) and dissolved oxygen (DO) using a water testing kit (Pro-lab TM , Florida).

Statistical Analysis
Data collected from the experiment were subjected to one-way analysis of variance (ANOVA) using SPSS package version 20 and the differences among treatments were separated using Duncan multiple range test (Duncan 1955).

Results
Water Quality Water quality parameters recorded during the experiment are presented in Table 3. There was no significant difference (P˃0.05) in all the parameters. The range for pH was observed to be between 6.32±0.08 to 6.83±0.17. Dissolved oxygen ranged between 6.36±0.15mg/L -6.83±0.17 mg/L, while temperature between 27.33±0.33 o C -28.67±0.33 o C.

Water Quality
The values for physico-chemical parameters observed in current study were within the tolerance range of C. gariepinus (Table 3) and agree with the findings of Adekoya et al. (2004). Bhatnagar et al. (2004) reported that the levels of temperature as (25-30 o C) is ideal for culture of C. gariepinus. Adekoya et al. (2004) also recommended dissolved oxygen level of between 4-8mg/L. Bhatnagar et al. (2004) reported dissolve oxygen level greater than 5 mg/L support good fish production. Bhatnagar et al. (2004) also suggested that 1-3 mg/L has sublethal effect on growth and feed utilization; 0.3-0.8 mg/L is lethal to fishes and oxygen concentration above 14mg/l is lethal to fish fry, and gas bubble disease may occur. Santhosh and Singh (2007) reported that the suitable pH range for fish culture is between 6.7 and 9.5 and ideal pH level is between 7.5 and 8.5 and above and below this could be stressful to the fishes.

Growth Performance
The present study investigated the effect of replacement of maize with MSM on the growth performance and feed utilization of African catfish (C. gariepinus). Among the diets, T5 (100% MSM) recorded the best growth performance which reflected in the values obtained for MFWG, FCR, SGR, and PER (Table 4). While T5 (100% MSM) recorded the highest weight gain, lowest FCR, highest SGR and the highest PER among the experimental diets, this result collaborates the findings of Iheanacho et al. (2017) who reported increased growth when Nile tilapia (Oreochromis niloticus) juveniles were fed melon seed peel based diet in 56 days feeding trial. Orire and Ricketts (2013) reported better growth performance and feed utilization efficiency when O. niloticus were fed melon seed peel based diet. Nwanna et al. (2009) reported poor feed utilization of potato peel based diet as dietary carbohydrate source in the diet of C. gariepinus. The findings of the present study differ from the report made by Jesu et al. (2008) on the utilization of various dietary carbohydrate levels by the freshwater catfish Mystus montanus. The disagreement may be due to the higher protein content of MSM (14.88%) when compared to 8.11% in potato peel. Values for FCR, MFWG, SGR, PER and mortality) were optimal and similar to the result reported by Amanat and Nasser (2001). Diet 2 (25% MSM) recorded the poorest growth response indicating poor feed utilization by the fish. This was expressed in the values of its biological evaluation such as high FCR, low MWG, SGR and PER values ( Table 4). The results of this study disagree with the observation made by Nwanna et al. (2009), who reported that very high inclusion levels of unconventional dietary carbohydrate sources often result in poor performance of the fish. The growth response of the control diet (T1, 0%MSM) was the second to least which was in agreement with the reports of Solomon et al. (2007) and Nwanna et al. (2009). Fagbenro et al. (2000 reported a comparable performance of Acha (Digitaria exilix) meal with maize and sorghum meal as dietary carbohydrate source for Nile tilapia. Nwanna (2003) showed the effectiveness of replacing maize with acha in the diets of Nile tilapia (Oreochromis niloticus). Nwanna et al. (2004) also reported that replacing maize with a non-conventional carbohydrate source tamarind (Tamarindus indica) resulted in good growth performance of catfish and improved economic returns.
Our results showed that C. gariepinus effectively utilized feed formulated with different dietary inclusion levels of MSM based diet especially diet 5 (100% MSM). This implies that MSM is an agro waste product to efficiently replace maize as carbohydrate source in the diet of Clarias gariepinus. Fish farmers are encouraged to explore this opportunity as it will reduce drastically the cost of fish production and enhance growth of fish as well.