Fish like any other organism; require nutrients for growth, development, reproduction and maintenance (Ejidike, 2004). Ingredients used for fish diets are chosen based on cost of nutrient content, availability and acceptability to fish (Eyo, 1997). Feed accounts for the highest proportion of the operational input in fish culture. Current researches in animal nutrition are focused on the use of alternative cheaper energy resources that could replaced cereals and supply the required nutrients in adequate amount (Adejumo, 2005). This is because the rising cost of some feed ingredients such as fish meal seems to hinder the economic relevance of fish culture.

This study observed that mean weight gain of the experimental fish increased with increasing hydrothermal processing duration (Table 1-3). This agrees with the report of Kaankula (1998) who reported that the nutritive value of legume seeds is improved when subjected to heating. This finding is similar to that report by Ejidike and Ajileye (2007) that diets formulated for Clarias gariepinus using thermally processed breadfruits seed meal has great potential in providing adequate nutritional feeds and at a reduced cost. Tuleun and Igba (2008), also reported that toasting alone recorded significantly improvement on the efficiency of feed utilization compared to the raw watermelon diet when fed chicken. However Tamminga, Egan and Chritensen, (2004) had stated that boiling of protein supplement may results in decreased animal’s performance for reasons of protein destruction. Ullah, (1982) also reported that heat treatment will affect the nutritional value of legumes through destruction or inactivation of present factors as well as some impairment in the protein value, because over heating may result in damaging the protein quality by lowering digestibility (denaturation) and causing the loss of sulphur amino acids. This study however as shown that boiling Citrullus lantanus up to 40 minute is not lethal to protein of water melon seed nor feed utilization of Clarias gariepinus feed diet with inclusion levels of this diet, as growth was far better and survival rate in all the treatments, still remain at 100 %. Furthermore EL Adawy and Taha (2001) had reported that watermelon seeds are rich in nutrients that promote growth and health hence might have been the reason for good nutrient utilization and survival rate attained in this study.

Table 1 Proximate composition of the experimental diets containing hydrothermally processed watermelon seeds

Table 2 Growth performance and nutrient utilization of Clarias gariepinus fed hydrothermally processed watermelon seed meal

Table 3 The proximate composition of carcass of Clarias gariepinus fingerlings fed thermally processed watermelon seed meal

In addition the present study revealed that the proximate analysis of the carcass fish fed the experimental diets were affected in terms of crude protein and fat content by the hydrothermally processed watermelon seed meal. Both the crude protein and lipid content of the fish carcass increase as hydrothermal processing time increased and were higher than the control diet. This is an indication of protein addition and true growth involving an increase in the structural tissues such as muscles (Fafioye, Fagade, Adebisi, Jenyo and Omoyinmi, 2005). Reinitz and Hitzel (1980) reported that the type of feed ingested and their nutritional quality is known to be one of the main factors affecting fish carcass composition. Increase in lipid observed in this study is in line with the reports of Chou and Shiau (1996); Ahmadi (2004) and Pei, Xie, Lei, Zhu and Yang. (2004). The differences in lipids is at variance with the study of Izquierdo, Obach, Arantzamedi, Mentorol, Robaina and Rosenwind, (2003), who however reported that lipid deposition in either liver or muscle of Seabass or Seabream did not differ significantly using the experimental diet. Also according to El-Marakby (2006) no change in total lipid and ash content was observed in fish fed different oil sources. This study has demonstrated that 40minute hydrothermal treatment of watermelon seed meal increase digestibility in the diet of Clarias gariepinus (Figure 1).

Figure 1 Weekly weight gain of Clarias gariepinus fed thermally processed watermelon meal diets for 8weeks

Wang, N. D. Hatcher W., Toews R., and Gawalko E. 2009, Influence of cooking and dehulling on nutritional composition of several varieties of lentils. Food Science Technology, 42(2): 842-884
http://dx.doi.org/10.1016/j.tifs.2009.01.005
http://dx.doi.org/10.1016/j.tifs.2008.10.006