1 Introduction
The major recurrent cost in fish production is feed; this alone has progressively taken the larger share of the cost of production so much that total feed cost accounts for over 60% of total production cost (Balogun et al., 1992). Tiamiyu et al. (2007) had reported that feed may account for between 60 – 80% of production cost for fish hence, the need to focus on least cost feed through the use of unconventional feed stuff. Conventional feed ingredients used in fish production are becoming increasingly expensive due to competition from humans (FAO, 2002), therefore efforts have been channeled to investigating other alternative feed ingredient which are unconventional in nature and are not edible by man as possible replacement for conventional feed ingredients in the diet of fish.

Many Agricultural by-products that are considered as wastes in Nigeria have great potentials as animals feed ingredients if properly handled, processed and incorporated into rations. A good example of such wastes is kola pod husk (KPH). Nigeria is one of the. Largest producers of Kola and Kola pod husk, it constitute 75% of the kola fruit. It has been reported to have 13% crude protein and energy of 2546.9kcal/kg (NRC, 1984) hence has high potential for consideration as possible substitute to conventional feedstuffs. The paucity of information on the nutritive values of Kola pod husk in the nutrition of African catfish necessitated this research which seeks to evaluate the growth performance and nutrient utilization of African catfish fed varying levels of Kola pod husk as replacement for maize.

2 Materials and Methods
The study was conducted at the Fisheries research farm University of Agriculture, Makurdi, Benue State using outdoor pond culture system with hapas (1m × 1m × 1m) and lasted for a period of 8 weeks. Clarias gariepinus juveniles used for this study were obtained from the department of Fisheries and Aquaculture, University of Agriculture, Makurdi, fish farm, they were acclimatized for three weeks before randomly distributing into the hapas.  Ten juveniles of the same mean initial weight were stocked in each hapa. The nylon mosquito netting material was purchased from North Bank, Market, Makurdi, Benue State of Nigeria. A nylon twine was also purchased to anchor the hapas firmly in the pond.

Fishmeal, vitamins and mineral premix were obtained from vitalfeed shop, Onitsha Street, Wurukum, Makurdi. Soybean, maize was purchased from North Bank Market, Makurdi. Kola pod husk was obtained from Cocoa Research Institute of Nigeria (CRIN), Ibadan, Oyo State, Nigeria. Twenty five kilograms each of kola pod husk was sun dried for a week to a constant weight. The dried husks were milled and sieved to powder and stored in airtight, moisture free container for feed formulation.

Five kilogram of soybean was toasted in an electric oven set at 1000c for 30 minutes (Eyo, 1999) allowed to cool and milled to obtain soy bean meal (SBM) and stored appropriately. Five kilogram of maize were also milled to obtained yellow maize meal (YMM) and stored according at room temperature. The ingredients were measured using head pan scale weighing balance.

All the experimental diets in the study were formulated using Pearson Square method. 40% crude protein diets were prepared to meet protein requirement for the fish with KPH replacing maize meal at varying level {Control (KPH 0%) Diet 1 (KPH 25%), Diet 2 (KPH 50%), Diet 3 (KPH 75%), Diet 4(KPH 100%)} as shown in Table 1. The feed ingredients for each of the Diet were weighed, ground, mixed thoroughly and warm water was added then stirred to form consistent dough which was passed through a 2mm die pelleting machine. The pellets produced were sundried to constant weight; the dried pellets were stored for the feeding trials which lasted for 8weeks.
 

Fifteen Clarias gariepinus fingerlings were evenly distributed in each of the hapa. The daily feeding was done by hand at 5% of the cumulative body weight of each hapa. The daily ration was divided into two feedings per day (08:00 and 16:00) and the fingerlings were weight weekly so as to adjust the feed by virtue of weight gained. A Tefal electronic digital scale was used to measure weights of fingerlings per week till the end of the experiment (8 weeks), growth performance were estimated as stated below.

(a) Mean Weight Gain (MWG) = Mean final weight – Mean initial weight

(b) Feed conversion ratio (FCR ) =

(c) Specific Growth Rate (%/day) = 

Where Wt1= Initial weight gain
Wt2= Final weight gain
T2-T1= Duration (in days) considered between Wt2 and Wt1

(d) Protein efficiency ratio = 

Where Protein fed =

(e) % survival rate =

Proximate compositions of KPH, diets formulated, initial and final carcass of fish were determined according to standard methods by AOAC (1990). However Nitrogen free extracts in samples were determined by difference. The analyses were conducted in triplicate and all reagents were of analytical grade.

The data obtained from the study were analyzed using Gen stat® discovery edition 4 and Minitab® 14, descriptive statistics were done and mean gotten were subjected to analysis of variance, where significant differences were obtained (P<0.05), means were separated using Duncan’s least significant difference (LSD).

3 Results
Proximate composition of Diet with inclusion of KPH is shown in Table 1, result obtained reveals the moisture content were significantly higher in Diet 4 (9.44%) while lower value (8.22%) were observed for the control diet. Ash content ranged from 13.48% in diet 4 to 8.42% in the control diet, the same trend of low value was observed in fibre (6.21%) in the control compared to the higher value recorded in Diet3 and 4 (7.43%), however highest values were observed for Lipid, and NFE (6.01% and 29.33% respectively) while diet 2 (3.31%) and diet 3(25.17%) had lower value respectively for this parameters. Trend of protein reveals increase in protein content as KPH increased in the diet from Diet 1 (41.81) to Diet 5 (50.17). Table 2 shows the growth and nutrient utilization of fish fed diets with inclusion levels of KPH as replacement for maize. Result reveals that Final weight, weight gain Protein efficiency ratio, percentage survival and specific growth rate did not differs significantly when control diet are compared to the experimental diets. Specific growth rate (SGR) ranged from 2.02 in control diet to 1.98 in Diet 4, Weight gain ranged from 6.30 (Control) to 6.18 (diet 4), while final weight ranged from 9.29 (Control) to 9.23 (diet 4) PER range from 1.06 in Diet 2 to 0.98 recorded in the control diet. Survival was between 67.5% (Diet 3) and 75.0% (recorded in diet 1 and control diet). However, FCR was significantly higher in Diet 4 and control diet (2.20) compared to other experimental diets while Diet 2 had higher value of Apparent net protein utilization (0.49) compared to other diets and the control diet. Result of the pattern of weekly growth of African catfish fed KPH based diet is shown in Figure 1, which reveals growth for Treatment 1, 3, 4 and the control diet to overlap through the weeks, however, treatment 2 was slightly below them. Proximate composition of Carcass of fish fed KPH based diet is shown in Table 3. Result obtained reveals that the experimental diets had significantly higher values for most proximate component compared to the values obtained for the initial analyzed carcass before the feeding trial. Diet 1 was observed higher in Ash, Lipid, and protein values and these values generally decreased as the level of inclusion level of KPH increased. Ash content ranged from 3.29% in Diet 1 to 2.73 in Diet 4. Fibre was higher in Diet 2 and 3 (2.14%) compared to other diet and the least value was observed in Diet 1 and 2 (2.10), Protein ranged from 17.27 % in Diet 1 and 3 to 16.61 in the control diet, Moisture was higher in the control diet and Diet 3 (70.10%) while least values were observed in Diet 2 (68.88%).
 

4 Discussion
Only few study has consider the nutritive value of KPH, the protein content observed in this study were higher than 15.0 reported by Osineye et al. (2008). Nutritional component of unconventional feed vary with their composition, origin and processing methods, 20.87% CP was reported by Mustafa and Alamin (2012) for watermelon seed while Elezuo et al. (2011) and Essien et al. (2009) reported 16.95% and 24.51% respectively for the same unconventional feedstuff. Akegbejo-Samson et al. (2004), Sotolu and Byanyiko (2010) and Tiamiyu et al. (2014) had also reported 9%CP for Parkia biglobosa. Solomon and Okomoda (2012) reported Crude protein of duckweed to be 17.6% while Erdal et al. (2004) and Flavia et al. (2008), had earlier reported 18.38% and 38.03% CP for wet and dried duckweed respectively. According to, the report of Falaye and Oloruntuyi (1998), the usefulness of unconventional feedstuffs in fish diets depends on certain factor such as palatability, proximate composition, digestibility and availability of nutrients. The protein value of KPH and previously reported nutrient component is higher than some conventional energy sources such as maize hence may be suitable for incorporation in fish feed to reduce feeding cost of the fish.

Kola-pod husk is a by-product during Kolanut production, and over 1.5million tones is disposed off in Nigeria annually (Opeke, 1984), constituting on environmental nuisance and costing the government so much money to render it physically, chemically and biologically harmless. Harnessing this by- products and. utilizing it in the formulation and compounding of Livestock (especially fish) feed, will not only eradicate its environmental disturbance in the kola nut producing areas, but will remove the rivalry for maize between man and animals, thus bringing about a great reduction in the cost of producing livestock feed and hence reducing the cost of producing fish, and other livestock. The result of this study on KPH as a feedstuff (major energy source) in Diet of Clarias gariepinus diets revealed that up to 100% maize can be substituted with KPH without significant (p>0.05) effect on growth and nutrient feed utilization. Hence suggesting an equal palatability and acceptability by fish, similar assumption were also made by Osineye et al. (2008) when they observed that Tilapia fed 100% KPH were comparable to those fed 100% maize meal. The idea of substituting by-product for conventional feedstuffs seems to have a general trend. Reports from several authors usually concludes that increasing inclusion of most of these by-products to the level of total replacement spells a live weight reduction (Adebowale and Olubamiwa, 2008; Olubamiwa, 2011). Bioflavonoid has long been identified as a plant growth promoter in Garcinia kola seeds (Braid, 1991) nutritional trial also shows better growth performance at inclusion level of 100gKg-1 by Solomon et al. (2014), hence since KPH is a byproduct of Kola, it is strongly believed that it contains some quantity of bioflavonoid thereby improving growth rate. Gross energy content of maize has been reported to be slightly higher in maize than that of KPH (Osineye et al., 2008) however the effect of this difference in gross energy may have been cushioned by much higher protein level in KPH observed to be higher than maize and thus was reflected in the average growth rate observed in this study, which was slightly higher but not significant (p>0.05) than the average weight of those on KPH diet. The slightly higher but not Significant Feed Conversion Ratio observed in the diet with inclusion of KPH could be attributed to higher crude fibre in KPH, thus reducing the digestibility of the KPH, relative to that of maize with a consequent relative decline in the efficiency of KPH diet, thus raising the Feed Conversion Ratio. Feed efficiency Ratio may not speak much about the expected economic performance of a diet, yet it is a good indicator of biological efficiency. The close numeric values observed in the diets may be inferred as indication of equivalent biological efficiency. The combination of similar weight gain FCE, FCR and presumed lowered feed cost per gram weight gain of the test organism feed the experimental diet compared to the control is a welcome development as demonstrate the biological and economic suitability of the use of KPH in complete replacement for maize in the diets of Clarias gariepinus.

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