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The zeolites are hydrated aluminosilicates, crystalline, microporous, which have several applications, due to their singular physicochemical characteristics, as the ionic exchange and the adsorption-desorption properties (Ghasemi et al. 2016). Its main use in the aquatic sector was aimed to improve the water quality of farms and fish transportation tanks by the selective collecting of NH4+ and toxic heavy metals(Aly et al. 2016 and Martínez et al. 2019).
In close systems or with water recirculation in aquaculture, the NH4+ produced by the feces decomposition and non- intake food is one of the main causes of mortality in fishes. The biological nitrification is the most common method for their elimination, although it has been informed that processes based on the exchange of zeolite ions resulted effective to control the nitrogen content in the culture water (Motesharezadeh et al. 2015).
According to Castro (2014), in the production of land animals, zeolite improves the efficiency in the nutrients use, specially the proteins sources. Therefore, it favors the growth rate and the productive yield, in addition, allows substituting certain raw matters percentages in feeds for monogastric and ruminants animals.
The available references in fishes about zeolite as a resource to stimulate growth and improve feed efficiency are few, and it is still a discussing theme. The objective of this study was to evaluate different substitution percentages (1, 3 and 5) of tilapia small fish feed by natural zeolite in the feeding of Nile tilapia GIFT (Oreochromis niloticus).
Materials and Methods
The experiment was carry out in the Laboratorio de Nutrición de Peces de la Empresa de Desarrollo de Tecnologías Acuícolas (EDTA), La Habana, Cuba, from June 17 to August 15, 2019. The experimental units consisted in 12 circular cement tanks, of 68 L capacity, with constant water fluid (turnover of 100 % daily).
Small fishes of Nile tilapia GIFT (Oreochromis niloticus) were used, from the genetic area of EDTA. They were acclimatized a week in the laboratory with tilapia small fish feed (FTF). After this time, a total of 240 animals were captured and selected, with 0.11± 0.03 g of initial weight, at random distributed according to one-way model, with four treatments and three repetitions. A total of 20 animals were placed in each tank. Daily, the dissolved oxygen and the temperature values were recorded, using a portable digital oximeter (HANNA®, Rumania).
The experimental zeolite came from San Andrés plant, in Holguín, Cuba. This product was marketed named Zoad and have a granulometric lower than 0.8 mm.
Four treatments were established: a control, that corresponded with the FTF (table 1), and three experimental diets (D), which consisted on the substitution of 1, 3 and 5 % of FTF by the zeolite (table 2).
Table 1 Percentage and chemical composition of tilapia small fish feed (control)
| Ingredients | % |
|---|---|
| Fish meal | 12.0 |
| Soybean meal | 40.0 |
| Corn meal | 22.4 |
| Wheat bran | 20.0 |
| Vegetable oil | 3.0 |
| Dicalcium phosphate | 1.6 |
| * Vit-mineral mixture | 1.0 |
| Total | 100 |
| Dry matter | 88.1 |
| Crude protein | 29.57 |
| Ether extract | 6.59 |
| Crude fiber | 4.13 |
| Ashes | 7.43 |
| Digestible energy(MJ/kg) | 12.16 |
*Vitamin-mineral mixture (kg of diet): vitamin A, 500IU; vitamin D, 100IU; vitamin E, 75 000 mg; vitamin K, 20 000 mg; vitamin B1, 10 000 mg; vitamin B3, 30 000 mg; vitamin B6, 20 000 mg; vitamin B12, 100 mg; vitamin D, 60 000 mg; niacin 200 000 mg; folic acid, 500 mg; biotin, 0.235 mg; selenium, 0.2 g, iron, 80 g; manganese 100 g; zinc, 80 g; copper, 15 g; potassium chloride, 4 g; manganese oxide 0.6 g; sodium bicarbonate, 1.5 g; iodine, 1.0 g; cobalt, 0.25 g.
Table 2 Percentage and chemical composition of the experimental diets (g /100 g)
| Ingredients | D-I (1%) | D-II (3%) | D-III (5%) |
|---|---|---|---|
| Commercial feed | 99 | 97 | 95 |
| Natural zeolite | 1 | 3 | 5 |
| Total | 100 | 100 | 100 |
| Dry matter | 89.26 | 89.1 | 90.12 |
| Crude protein | 29.24 | 28.65 | 28.10 |
| Ether extract | 6.50 | 6.38 | 6.26 |
| Crude fiber | 4.08 | 4.00 | 3.92 |
| Ashes | 8.62 | 10.06 | 12.10 |
| Digestible energy (MJ/kg) | 12.04 | 11.80 | 11.55 |
Diets preparation. For the elaboration of the FTF, soybean, corn meal and the wheat bran were ground in a nativa hammer mill (250 µm) and mixed in a mixer (HOBART MC-600®, Canada). The oil and the vitamins and minerals premixture were added. Later, the feed was divided in four same portions for the inclusion of the different zeolite levels. From each portion (treatment), a part was used as meal for the feeding in the first stage, and the other one was pelleted in a meat grinder (JAVAR 32, Colombia) at 1 mm diameter. Later, they were dried in an oven (Selecta, España) at 60 oC for 24 h.
The diets were offered as meals in the first 30 d and later in1 mm pellets. They were supplied in four rations, at 8:00, 11:00, 14:00 and 16:30 h, during 60d.The feeding rate was at 20 % of the body weight per day, which was fitted every 15d. At the end of the bioassay the fishes were individually weighed for the calculation of the fallowing productive indicators:
Supplied food= food added/ number of final animals.
Supplied protein = supplied protein/number of final animals.
Final average weight.
Feed conversion factor (FCF) = Food added /weight gain.
Protein efficiency = Biomass gain /supplied protein.
Survival (S) = Number of final animals / number of initial animals x 100.
Bromatological analysis. The methods described by AOAC (2016) were applied to the meals. From the results, the nutrients contributions of each diet were determined. The digestible energy (DE) was calculated with the caloric coefficients referred by Pezzato et al. (2001).
Statistical analysis. The normality and homogeneity assumptions were proved. A one -way ANOVA was performed by the statistical package INFOSTAT, versión 2012 (Di Rienzo et al. 2012).When there were differences (P < 0.05), means were compared by the Duncan (1955) test.
Economical analysis. Was performed according to Toledo et al. (2015) procedure. The experimental rations costs were calculated out of the international prices representative of the raw matters for February 2020 (www.fao.org/giews/pricetool) (table 3). To the results were added 45 % of the total expenses of raw matters per concept of additional expenses (transportation, maquila and administrative for Cuba). These values were multiple by the FCF obtained in this study in order to know the feeding costs.
Results and Discussion
The temperature and the dissolved oxygen in the water of the tanks oscillated between 26.1 and 27.4oC, and between 4.54 and 5.35 mg/L, respectively. These values are considered adequate for the good productive performance of the species (Costa et al. 2017). In addition the water circulation was efficiently controlled and 100% of the daily turnover was guaranteed.
The experimental diets had good acceptation, which showed that the rations palatability was not affected by the evaluated zeolite levels. In the same way, when the food was supply in pellets, the stability of them in the water was good, which could be related with the agglutinating effect of the mineral, as Abdel-Rahim (2017) reported. According to this author, zeoilte was register in the European Union as a feed additive (agglutinating, anti-strengthen agent and coagulant), recommended in artificial foods to reduce the toxic effects of aflatoxins, and antimicrobial agent.
Among the main advantages of the zeolite use in fishes is their action in the control of micotoxins and in the reduction of toxic effects of aflatoxins, as well as in the increase of food intake. The zeoilite also take part in the feed conversion decrease by high efficiency in the protein use, which lead to growth increase and the mortality decrease (El-Gendy et al. 2015 and Abdel-Rahim 2017).In addition, it can improve the quality of culture water by the ammonium ions collecting, which positive influences on the animals welfare and on the effluents which are threw to the environment (Ghasemi et al. 2016 and Martínez et al. 2019).
There were differences (P < 0.05) in the indicators related with the amount of food and protein per animal from 3 % the zeolite inclusion (table 4).This is due to the growth was not affected and, therefore, the amounts of supplied food were similar. When substituting 3 and 5 % of feed by zeolite, these indicators decreased with respect to the control and the D-I, where only 1% of feed was substituted.
Table 4 Productive performance of the small fish of Nile tilapia with the experimental diets.
| Indicators | Control CP | D-I 1% | D-II 3% | D-III 5% | ± SE Sign |
|---|---|---|---|---|---|
| Amount of food /fish (g) | 9.08 a | 8.54 a | 7.51b | 6.50 c | 1.07 P=0.001 |
| Amount of protein / fish (g) | 2.95 a | 2.76 a | 2.39 b | 2.09 b | 0.10 P=0.001 |
| Final weights (g) | 5.88 ±0.46 | 5.84 ±0.6 | 4.89 ±0.32 | 5.79 ±0.43 | P=0.404 |
| Feed conversion | 1.52 a | 1.44 a | 1.50 a | 1.19 b | 0.05 P=0.001 |
| Protein efficiency | 2.03 a | 2.16 a | 2.04 a | 2.63 b | 0.09 P=0.001 |
| Survival (%) | 86.66 | 95.67 | 90.00 | 90.00 | 1.75 P=0.24 |
abDifferent letters in the same row statistically differ to P < 0.05, according to Duncan (1955)
The final weights did not differ between the experimental diets (table 4), which shows that the inclusion up to 5 % of zeolite was feasible in the ration of small fish of Nile tilapia. It is important to highlight that this treatment had the lower supplied protein per animal (table 4) , and did not affected the small fish growth with respect to the control and the D-I (1%), which can support those reported by Abdel-Rahim (2017) with respect to the positive effect of adding zeolite on the fishes growth.
Several reports showed the direct relation between the fish growth and the dietetic protein intake (Toledo et al. 2007 and Mejías et al. 2016). In this study was showed higher efficiency in the protein use with the zeolite incorporation. This is reaffirmed in the values of feed conversion and protein efficiency (table 4), that significantly improves with 5 % of this mineral. In addition, in this experiment is corroborate those informed by Kanyilmaz et al. (2015), who found higher digestibility coefficients of dry matter and protein in diets supplemented with 5 % of zeolite in common carp (Cyprinus carpio).
Galindo et al. (2006) evaluated 3% of natural zeolite (clinoptilolite and mordenite) from Tasajeras deposit, in Villa Clara province, in the food of young white shrimp Litopenaeus schmitti. These authors did not obtained statistical differences in the growth between the animals that intake the food with zeolite and without it, but there were in the feed conversion. These showed the best use of the food in which zeolite was included, result that coincides with that obtained in this study with tilapia.
El-Gendy et al. (2015) developed a study at productive scale, with 2 % of zeolite in the ration of small fish of Nile tilapia and a feeding rate of 2, 2.5 and 3 % of body weight. These authors informed the best indicators of water quality (pH, ammonium, nitrite, nitrate and alkalinity) and productive, with 2.5 % of biomass. Steica and Morea (2013), when studding the effect of natural zeolite on fish food, concluded that it agglutinating effect improves the food stability and reduce the wastes. In addition, increase the palatability and expose for more time the bolus to the effect of the digestive enzymes, that is why is was consider a growth promoter.
Aly et al. (2016) compared 5 and 10 ppt. of natural zeolite with a probiotic product, effective microorganisms (EM) of EMRO Japan, which added to 400 ppm in the culture water of European sea bass Dicentrarchus labrax larvaes. There were not differences in the final weights, but survival was high in the treatment with EM. These result was attributed to the effect of this lasts on the improvement of microorganisms balance in the intestine, to the immune system strengthen and to the contribution they made to the water quality. In the treatments with zeolite the efficiency in the ammonium elimination was higher.
In this study, the survivals did not showed differences (table 4), contrary to that informed in Larmoyeux and Piper (2006) study. These authors reported low incidence of bacterial diseases and mortality, when zeolite was used in fish rations, which is explained because their antimicrobial effect. The values reached were higher to the 60% informed by Aly et al. (2016) in European sea bass larvae with natural zeolite, and resulted slightly lower to 94 % obtained in Nile tilapia by El-Gendy et al. (2015).
The economical analysis (table 5) showed that the use of increasing zeolite levels decrease the rations costs, because of it lower price with respect to the commercial feed. In addition, the highest savings were with the use of 5 %, due to be the ration of lower cost, and with which the lower feed conversion was obtained. These results corroborate the El-Gendy et al. (2015) and Abdel-Rahim (2017) studies.
Table 5 Economical analysis of Nile tilapia production, with 1, 3 and 5 % of natural zeolite (US $ /t)
| Indicators | Control CP | D-I 1% | D-II 3% | D-III 5% |
|---|---|---|---|---|
| Ration cost | 593.57 | 588.38 | 578.01 | 567.64 |
| Feeding cost | 902.23 | 847.27 | 867.01 | 675.49 |
| Savings | - | 54.96 | 35.22 | 226.74 |
It was showed that the substitution of 5 % of commercial feed by Cuban natural zeolite did not affected the growth of small fish of Nile tilapia GIFT, and improved the used of food (conversion and protein efficiency) with a positive economic effect. It is proposed to developed new researchers that evaluate the zeoilite as replacement of protein raw matters (fish and soybean meals) in the feeding of this species.
