Much information is given (Willem Van Cotthem, 2012) about Opuntia ficus-indica as an aloes. Therefore, the aim of the present study was evaluating the possibility of using powders of either fruits' skins or leaves of the Egyptian Teen Shoky as replacers for dietary corn in all-males mono-sex Nile tilapia, Oreochromis niloticus diets and their effects on fish performance for 75 days. This is an attempt to ameliorate feed costs by substituting such costless wastes in fish diets to replace somewhat imported dietary ingredients to save foreign money.
Materials and Methods
Experimental animals and their management:
Hundred all-males mono-sex Nile tilapia, O. niloticus fingerlings weighed on average 17 g and had on average a total length of 9.2 cm purchased from a private fish hatchery (Al-Emam) at Tolompat 7 (Kafer El-Sheikh Governorate) were transferred in plastic bags to Sakha Aquaculture Research Unit. Then, the experimental fish were adapted in a plastic tank of 1m3 on the experimental Lab. conditions for one week. Thereafter, these fish were randomly divided into 10 glass aquaria at a stocking rate of 10 fish/aquarium that had dimensions of 70 x 35 x 40cm and filled with 65 liter of fresh water each. The feeding trial duration was 75 days (from 10/7/2017 till 25/9/2017); during which, each two aquaria (replicates) were singed to each treatment. Fish were initially weighed and biweekly thereafter to readjust the feed quantity must be offered per each aquarium according to the actual body weight changes, maintaining the daily feeding rate at 3% of the biomass. The aquaria water was partially changed via syphoning five times weekly and once totally every week. The rearing water was dechlorinated tap water, since fresh tap water was aerated in a large tank to remove chlorine before be used. Some quality criteria of fish rearing water were periodically measured throughout the experimental duration. The source of light in the experimental lab. was naturally about 10 hours light and 14 hours darkness. Fish rearing water temperature was kept constant via heaters with thermometers.
Five experimental diets were formulated to replace 25 and 50% of dietary corn by fig skins and leaves in diets (D) No. 2, 3, 4, and 5, respectively besides the control one (diet No. 1) as shown in Table 1. All dietary ingredients were purchased from the local market (Makka Factory for fish diets, Kafr El-Sheikh). Fig fruit skins, as well as fig plant leaves, were collected and separately sun dried then ground. All experimental diets were formulated by manually mixing all ground ingredients, then pressed and pelleted into sinking diets with an average pellet diameter and length of 2 and 1 mm, respectively using an electric pelleting machine. Diets were offered to fish 6 days a week at 2 meals (8 am and 2 pm) daily.
Measurements of the evaluation:
At the start and at the end of the experiment, fish body weight, and fish total length were measured biweekly. Feed consumption was also measured. Growth rates, condition factor, and feed conversion ratio were calculated (Froese, 2006 and Abdelhamid, 2009); where:
Specific growth rate (SGR, %/day) = 100 [In W2 – In W1] / period, days
Relative growth rate (RGR, %) = 100 [W2 – W1] / W1
Condition factor (KF, %) = 100 (Fish weight, g / fish length, cm3)
Feed conversion ratio (FCR) = Consumed food, g / fish body gain, g
Mortality rate (MR, %) = 100 (No. of die fish / No. of fish at the beginning of the experiment).
Some measurements in fish rearing water were carried out to determine the suitability of water quality for rearing the experimental fish rearing according to Abdelhamid (1996). Proximate analysis was carried out for the tested dietary ingredients, diets, and whole fish body (in 5 fish per aquarium) according to AOAC (2000). Dressing percentage, boneless meat percentage (fillet) and water holding capacity were calculated too (Abdelhamid et al., 2012).
The obtained numerical results were statistically analyzed using SAS (2006) and Duncan (1955) for statistical differentiation between treatment's' mean.
Results and Discussion
Fish rearing water quality criteria:
Table 2 shows that there were no marketable effects of the dietary treatments on the water quality criteria measured, and the registered values are within the suitable ranges required for rearing Nile tilapia cited by Abdelhamid (1996) and Abdelhakim et al. (2002).
Experimental diets' composition:
Both tested materials were chemically analyzed (Table 3). Teen Shoky fruit skin (peel) (TSFS) contains less dry matter, crude fiber and silica than Teen Shoky leaves (TSL). However, both materials are to some extent chemically similar, except the higher levels of crude fiber, ash, and silica in leaves than the fruit skins but the last contains higher fat and nitrogen free extract than the leaves. That perhaps means that the fruit skin may be more nutritious agent than the leaves.
The other dietary ingredients used in the experimental rations were also chemically analyzed (Table 4). Soybean meal is a plant protein source, since it contained 35.41% crude protein (CP); yet, the fish meal (from the local market) used herein as an animal protein source was of low CP content (16.33%). Wheat bran as a carbohydrate source contained lowest percentages of CP, crude fat and ash but the highest crude fibers (CF) and carbohydrates (nitrogen free extract, NFE) among the tested dietary ingredient.
The tested rations were chemically analyzed too (Table 5). Their moisture and crude fat contents were decreased to some extend by the dietary inclusion of fig wastes, particularly with TSL than TSFS and with increasing the inclusion level from 25 to 50%. The opposite trend was recorded for CP and CF that gradually increased in diets 2, 3, 4, and 5 than D1 and in D3 and D5 than D2 and D4. However, total carbohydrates content was equal in different diets. These slight variations in chemical composition of the experimental diets are due to the nature (chemical composition, Tables 3 and 4) and level of the fig wastes (TSFS and TSL) used herein. Usually any replacement affects the dietary composition as found by many authors used different dietary replacers (Abdelhamid and Saleh, 2015; Abdelhamid et al., 2016 and 2018).
The dietary inclusion of fig wastes; particularly with 50% TSFS (D3) and 25% TSL (D4) decreased (P≤0.05) the feed consumption (Table 6) of the experimental diets than the control (D1). That may be attributed to higher contents of CF and ash (Table 5) in fig wastes, particularly in TSL than the corn.
Dietary inclusion of TSFS and TSL improved (P≤0.05) either of FBW, TBG, DBG, as well as SGR and RGR (Table 7), particularly at 25% TSFS and 50% TSL. On the other side, these substitutes increased the MR of the fish as reported too by Abdelhamid et al. (2018). Table 8 shows that final total length and condition factor of the experimental fish did not affect (P>0.05) by the dietary treatments; although, FBW was significantly (P≤0.05) affected, since it was the highest with D2 and D5 (Tables 7 and 8). It is proved that increased dietary CP (Table 5) significantly elevates FBW and RGR (Table 7) as found by Abdelhamid et al. (2001) and Khalil et al. (2001). Moreover, some replacing agents significantly improved FBW, FBL and FCR (Abdelhamid et al., 2000).
Feed utilization expressed as feed conversion ratio (FCR) presented in Table 9 for the experimental fish for the whole period of the feeding trial clears the replacement of corn by fig wastes improved the FCR than on the control diet (D1), particularly it was significantly (P≤0.05) the best with D2 and D5. Abdelhamid et al. (2005) recorded better results with Nile tilapia by a dietary replacement concerning their growth performance, feed utilization, and their body CP content.
Fish body composition:
The chemical composition of the experimental fish at the start composed of 13.67% protein and 2.95% fat. After 75 days of the experimental feeding period, crude protein increased (17.42 – 19.25%) than at the start of the experiment, since dry matter content naturally increased by age and therefore all nutrients increased too. However, the tested material gradually increased (P≤0.05) both of protein and ash contents gradually as the level of these materials increased in the diet from 25 % (D2 and D4) to 50% (D3 and D5) and then the control (D1, without fig wastes). The opposite trend was recorded for the fat content that decreased by dietary inclusion of fig wastes (than the control), particularly with increasing the fig waste levels (P≤0.05). Generally, the negative correlation between protein and fat percentages is a fact (Ali, 2008; Salem et al., 2008; Saad, 2010 and Farrag et al., 2013). Yet, other researchers found a positive relation between CP and EE contents of fish body (Eweedah et al., 2006; Gaber, 2006 and Soltan et al., 2008). Others did not find the effect of dietary treatments on fish body composition (Mohamed and Hanafy, 2002; Soltan et al., 2002 and El-Dakar, 2004). Anyhow, some wastes fed to fish may reduce fish body fat content and increase ash content (Hassanen et al., 1995). Also, Kheir and Sweilum (1997) reported that increased dietary CP content led to increase fish body CP and lower its ash content. However, the carbohydrates level is naturally low thus did not affect by the dietary treatments (Table 10) which confirmed also by Abdelhamid et al. (2018).
Dietary replacements may improve FBW, TBG, DBG, RGR, SGR, FCR, and fish body CP (Abdelhamid et al., 2011). Consequently, many authors (Abdelhamid and Soliman, 2012; 2013; Abdelhamid et al., 2015 and Khadr, 2018) recommend replacing conventional feed ingredients with unconventional ones without any harms on fish health and performance. Although, some other replacers from polluted sources could be harmful for fish, thus did not recommend to be used in feeding fish (Abdelhamid et al., 2010a & b).
Based on the currently obtained findings, it is possible to feed all-males mono-sex Nile tilapia, O. niloticus diets containing fig wastes as replacers for dietary corn, particularly at replacement rates of 25% fig skin and 50% of fig leaves without adversely effects on productive performance parameters of fish.