Performance and digestibility of Nile tilapia fed with pineapple residue bran

. Two experiments were conducted, the first being the digestibility of feed and the second performance in an attempt to evaluate the residue of pineapple bran in diets for Nile tilapia. Eighty animals weighing 63.9 ± 0.79 g in a completely randomized design were used to test the digestibility in order to evaluate the apparent digestibility of dry matter, crude protein, gross energy, digestible energy and digestible protein. In the performance of 240 juveniles were distributed in three ranges of weights: 34.9 ± 0.06, 44.4 ± 0.27 and 55.5 ± 0.10 g, in order to evaluate performance, yield Housing and somatic indices of Nile tilapia. The design was a randomized block with three blocks, with four treatments and five repetitions, rations in both experiments contained four levels of inclusion of pineapple bran residue (0, 5, 10 and 15%). The digestibility of the diets were: dry matter (76.17, 75.42, 75.31 and 75.77%), crude protein (87.90, 90.24, 89.51 and 89.03%) gross energy (79.12, 79.33, 79.07 and 77.48%), digestible energy (3649, 3559, 3560 and 3190 kcal kg -1 ) and digestible protein (29.28, 30.35, 29.82 and 29.79%), respectively. It was observed the significant effect on the carcass without head, so we recommend the inclusion of up to 10.39% for the inclusion of pineapple bran residue in diets of Nile tilapia.


Introduction
The Nile tilapia (Oreochromis niloticus) is one of the prominent species of global aquaculture because of some intrinsic characteristics, such as rusticity and tolerance to low taxes of dissolved oxygen.Its flesh presents good sensorial characteristics and fillet with no intramuscular "Y" shaped spines (FURUYA et al., 2008a).At the intensive cultivation system they are used balanced commercial feed that, in general, presents a high coast, because generally they are used animal products and sub-products (LANNA et al., 2004a).Because of it, many efforts in researches have been realized to use alternative vegetal ingredients trying to replace the conventional ingredients to reduce feed costs, optimizing the productive yield of the animals.As alternative to Northeast Region, it can be used agro-industrial residue, because that region is prominent on cultivation of most of the tropical fruit species (LOUSADA JÚNIOR et al., 2005).
In Brazil, the cultivation intended to meet the demand of fresh fruits, however, there is a global tendency to processed products market, as conserves, juices, jams and sweets (LOUSADA JÚNIOR et al., 2006).After processing the fruits for obtaining those products, it is generated a huge quantity of residue, which majority does not go through any treatment before be discarded into environment.
Among agro-industrial residues, the pineapple ones deserve attention by being source of calcium and A, B, C vitamins and bromelain, enzyme belonging to protease group.This enzyme occurs on stalk, leaves, roots and pineapple fruit (FRANÇA-SANTOS et al., 2009).Generally, fruit pulp factories discard pineapple leaves, shells and the pressed bagasse that was made after obtaining the pulp.Indeed, to feed monogastric animals it is advisable the using of pressed bagasse bran, due presents a lower fiber content, in relation to the one made of leaves, shells and bagasse.
According to nutritional composition of pineapple residue bran, it is considered as an ingredient of energetic source, because Fialho et al. (2009) reports that for the ingredient be considered an energetic one, it must presents a percentage average under 20% of crude protein and under 18% of crude fiber.
So, the present research was made with the aim of evaluate the inclusion of pineapple residue bran on the apparent digestibility, productive performance, carcass yield and somatic index of Nile tilapia.

Material and methods
The research was conducted in the Laboratório de Digestibilidade de Não-Ruminantes do Departamento de Zootecnia da Universidade Federal Rural de Pernambuco -UFRPE.
The pineapple residue bran was obtained from a factory of pulp fruit obtaining, in Recife, Pernambuco State, made of fibrous bagasse, obtained from the pulp extraction.It was acquired in natura and passed through a pre-drying process, in which the one was exposed to the sun, spreads in a soft layer over a plastic canvas during an eight hours period.Then, it was taken to a forced ventilation stove at 65°C, for 48 hours, in which they were revolved twice a day, to make the dehydration easier and avoid the appearance of fungus.After dehydration, the material was processed in type knife grind, 2 mm sieved, to obtain the bran.After, it was carried to the Laboratório de Nutrição Animal do Departamento de Zootecnia da UFRPE, for analysis of dry matter, crude protein, ether extract, crude fiber, fiber in neutral detergent and fiber in acid detergent, according to the methodology described by Silva and Queiroz (2006) and the analyses of crude energy was made at Universidade Federal Rural do Semi Árido -UFERSA.
For processing the feed, the ingredients were crushed by a type knife grind, 1mm sieved, and then it was manually mixed until it acquires a homogeneous look.Then, the mixture was moistened with water in a temperature about 60°C and, then, it occurred the pelleting in a manual meat grinder.After the end of this process, the feed was taken to a forced ventilation stove at 65°, for a period of 24 hours.
The pellets were broken and separated by different sized sieves, for present the right diameter of animal's mouth.
After processing the residue and the feed they were started nutritional experiments, which were divided in two steps: firstly, it was made a test of feed digestibility, containing 0, 5, 10 and 15% of inclusion of pineapple residue bran, during 23 days, in which, 3 days for adaptation and 20 days for data collect.They were used 80 juveniles of Nile tilapia, with average weight of 63.9 ± 0.79 g.
The animals were distributed in 20 fiberglass conic aquariums, with 60 L capacity, continuous aeration system, being placed 4 animals per aquarium.It was adopted the entirely randomized design, with four treatments and five repetitions.The fishes were fed until apparent satiety with small fractions every 30 minutes from 8h until 16h 30 min., with four isoproteic and isoenergetic feed containing 0, 5, 10 and 15% of inclusion of pineapple residue bran, as described on (Table 1).These feed were added with 1,0% of Chromium oxide (Cr 2 O 3 ), for the test of digestibility.
At the end of the afternoon it was renewed all aquarium water gradually, where at the bottom of them there were stopcocks which were opened for water flow, and while the water flowed, there were hoses on the top of the aquariums for water renewal.This management was daily realized to avoid feed lefts with faeces samples.The collect was made at 8h, and the material stored in freezer at 0°C.
The apparent digestibility coefficient was calculated according to the formula described by Cho et al. (1985): where: Da(n) = aparent digestibility of nutrient; Cr 2 O 3 r = % of chromium oxide in feed; Cr 2 O 3 f = % of chromium oxide in faeces; N r = % nutrients in feed; Nf = % nutrients in faeces.
The second stage consisted of performance experiment, during 60 days.They were used 240 juveniles of Nile tilapia, mannish, distributed on three weigh levels: 34.9 ± 0.06; 44.4 ± 0.27 and 55.5 ± 0.10 g.It was adopted the design in randomized blocks with three blocks and four treatments (the same used at the digestibility test) with five repetitions.
The fishes were distributed in 10 boxes of (500 L), halved by a plastic canvas (1 cm diameter between knots), resulting in two experimental unities, where were stored 12 fishes each, staying so 250 L for each side.
The boxes were interconnected by a recirculation system of water, with an average flow of two liters of water per minute, using a biological filter, and a continuous aeration system by microporous stones, connected to a portable air compressor.The feeding was made five times a day: 9 to 17h, every two hours, until apparent satiety.
Water physico-chemical variables, as dissolved oxygen, pH, nitrite, ammonia and temperature were analyzed during all experimental period, every two days.The dissolved oxygen was monitored by digital oximeter, the nitrite, the pH and the ammonia, by colorimetric chemical tests, and the water temperature by mercury thermometer installed inside the boxes.These variables were analyzed always at 8h, before of siphoning, that was made at 8:30 for remove the feed and faeces lefts in the depth of the boxes.Each two days it was renewed 40% of the water in the boxes, what provided the maintenance of its quality.The fishes were submitted to a photoperiod of 12 hours of light.
At the end of the experiment, the fishes were kept unfed for 24 hours, being next sacrificed by thermal shock (water + ice).Posteriorly, they were collected biometrical data (total weight and size), it was made a ventral longitudinal incision and it was removed all the content of the abdominal cavity, including gonads and abdominal fat.From collected data there were evaluated the parameters of: hepatosomatic index, abdominal fat index and organs weights.To take yield data of carcass with head, it was weighed the carcass without the content of abdominal, and for the yield of carcass without the head, this one was sectioned from body around the junction with the spine, including gill, and it was removed the content of abdominal.
Obtained data were submitted do analysis of variance and regression using the software Statistical Analysis System (SAS, 2000).
Among nutrients contained in pineapple residue bran is the fiber that is more abundant.The fiber in  2006), evaluating the composition of pineapple residue bran, that was composed of added pulp shell plus the pressed pulp of juice obtaining, had found different values of bromatological composition from the ones found on the present study, for dry matter 84.7%, crude protein 8.3%, fiber in neutral detergent 71.4%, fiber in acid detergent 30.7%, ether extract 1.2% e mineral matter 6.8%.Correia et al. (2006), evaluating the bromatological composition of pineapple residue, being this constituted of shell plus pressed pulp from juice obtaining, had found values of dry matter 87.9%, mineral matter 10.1%, crude protein 7.4%, fiber in neutral detergent 72.1% and fiber in acid detergent 33.7%.
The processing way of the fruits by agroindustries, the cultivation place, the variety of the fruit and the way through the bran was made may influence on nutritional composition of pineapple residue bran.The results of digestible coefficients for dry matter, crude protein, digestible energy and digestible protein in function of the levels of inclusion of pineapple of residue bran are described on (Table 2).
It was observed a quadratic effect on digestibility for all parameters above, except for digestible protein, there was not a significant difference.
For the apparent digestibility coefficient of crude protein it was observed quadratic effect, however, the level that presented the best digestibility coefficient was the 5.0%.That might be occurred because of the percentage of crude fiber of feed, because of the increasing on fiber level from 3.51 to 4.20%, increasing, then, the viscosity of digestion more prominent.Sklan et al. (2004) quote that the high content of diet fiber decreases the access of digestible enzymes to nutrients or by indirect interaction among the components of cell wall or by digestible process.
According to Furuya et al. (2008a), diet fiber can reduce the digestibility of protein and amino acids throughout stimulation of bacterial-originated protein, occurring adsorption of amino acids and peptides for the fiber matrix and by the increasing of secretion of endogen protein.
The fiber reduces the digestibility of nutrients because it changes the passage rate.Lanna et al. (2004b) analyzing the effects of the crude fiber levels (2.5, 5.0, 7.5, 10.0 and 12.5%) on Nile tilapia feed, over the speed of gastrointestinal traffic, concluded that the increase of the crude fiber content of the feed decreases significantly the time of the gastrointestinal traffic.
The influence of the fiber upon the fishes is still few studied and may be connected to its percentage composition in celluloses, hemicelluloses, lignin and silica, among other (MEURER et al., 2003).
Although the inclusion levels of pineapple residue bran have interfered on digestibility of the protein, the results of coefficient of digestibility presented were satisfactory for a vegetal ingredient.Probably, these results were obtained, since the pineapple may be a source of proteolytic enzyme, bromelain, that is an enzyme of hydrolases classes and are able to break the peptide bond of proteins and peptides (FRANÇA-SANTOS et al., 2009).
However, this fruit has an anti-nutritional factor, the polyphenols, that may react, reversible or irreversibly with the protein, harming the digestibility and the bioavailability of lysine and of other amino acids essential (SANTOS et al., 2001).But, these anti-nutritional factors are present in stalk and leaves, parts that were not used for compose the bran used on this research, this fact can explain the good results of digestibility coefficient.
Generally, modifications that may occur on studied variables are directly related to accumulation of energetic reservations or to any disturb on metabolism of proteins and lipids, but the accumulation of fat is more evidenced on animals in finishing phase, that was not this research case, in which there were used juvenile animals.Yet, the deposition of corporal fat may also occur for other factors.Arbeláez-Rojas et al. (2002) relate that in conditions of confinement, where fishes' movements are restricted, it may happen an increasing on corporal fat, which decreases the quality of the product and may affect the acceptation by the consumer.
According to Santos et al. (2009), somatic index are important for better evaluation of physiological conditions, when the animal is submitted to feed with alternative vegetal food.Those products may contain relations with anti-nutritional factors present in these feed that would prejudice the normal functioning of fishes' organisms, causing problems to their metabolism.
The using of pineapple residue bran from agroindustrial processing may be considered as alternative source on fishes' feed, however, researches on nutritional way must be made for a better knowing of bromatological composition, nutrient digestibility and, consequently, testing appropriated levels on trying to obtain the best answer from the animal.

Conclusion
It is recommended the usage of until 10.39% of pineapple residue bran on feed for Nile tilapia without affect the yield of carcass without head.

Table 1 .
Percent and Chemical Composition of experimental feed with different levels of pineapple residue for Nile tilapia (natural matter based).

Table 2 .
Probability values (P), variation coefficient (CV) and averages of the aparent digestibility coefficients of dry matter (CDaMS), crude protein (CDaPB), crude energy (CDaEB), digestible energy (ED) and digestible protein (PD) of feed containing different levels of inclusion of pineapple residue bran for Nile tilapia.

Table 3 .
Probability values (P), variation coefficient (CV) and averages of initial weight, final weight, weight gain (final weight -initial weight (GP)), feed consumption (CR), apparent feed conversion (CAA) and survival rate (TS) of tilapias fed with different levels of pineapple residue bran.