Gastrointestinal tract pH measurement in juveniles Pacu Piaractus mesopotamicus (Characiformes: Characidae) WELLITON GONÇALVES-FRANÇA1, TÂNIA C.PONTES1, FABRÍCIO MARTINS-DUTRA1, FRANK LIEBERT2, EDUARDO L. CUPERTINO-BALLESTER1 & LEANDRO PORTZ1* 1 Universidade Federal do Paraná, Setor Palotina. Programa de Pós-graduação em Aquicultura e Desenvolvimento Sustentável, Departamento de Zootecnia, Rua Pioneiro, 2153, Jardim Dallas, 85950-000, Palotina, Paraná, Brasil. 2 Georg-August-University Goettingen, Institute for Animal Physiology and Animal Nutrition, Goettingen, Germany. *Corresponding author: [email protected] Abstract. The study evaluated pH differences along the digestive tract of the Piaractus mesopotamicus. The higher pH variation occurs in the stomach region, where it occurs to break down of the food through the gastric enzymes, which requires acidic action to perform such function. Keywords: aquaculture, nutrition, physiology, tropical fish. Resumo. Medição do pH do trato gastrointestinal em juvenis de Piaractus mesopotamicus (Characiformes: Characidae). O estudo avaliou as diferenças de pH ao longo do trato digestivo do Piaractus mesopotamicus. A maior variação do pH ocorre na região do estômago, onde ocorre a queBra do alimento através das enzimas gástricas, o que requer ação ácida para realizar essa função. Palavras-chave: aquicultura, nutrição, fisiologia, peixes tropicais. The pacu (Piaractus mesopotamicus) is an divided into three parts, head intestine (pharyngeal omnivorous fish with a strong tendency to herBivory, buccal cavity), foregut and hindgut (Moreira et al. feeding on organic detritus, plants and seeds. The 2001). The passage of food through the digestive species is highly appreciated due to the high quality tract of fish can be altered by various factors such as of meat, rusticity, fast growth and easy adaptation to the physical and chemical characteristics of the feed, production systems (Stech et al. 2010). The species the aBiotic factors of water that can influence the also can tolerate poor water quality and is resistant metabolism and amount of food consumed to pathogens (Abimorad & Carneiro, 2004). The (Possompes et al. 1975, Usmani & Jafri 2002, Dias- studies using pacu (Abimorad & Carneiro, 2007; Koberstein et al. 2005). Therefore, the study Bicudo et al. 2009) were carried out with the between the co-relations of the diet and the objective of maximizing the production potential of characteristics of the digestive tract has gained this species, among these, studies that refer to prominence in different zoological groups, being nutritional aspects has gained prominence. indispensaBle for the manipulation and formulation The morphological and physiological of balanced diets (Seixas Filho et al. 2000). characteristics of the fish are defined by species- According to Chakrabarti et al. (1995), the specific feeding habits, influencing the stomach pH, intestinal tract of the fish is in an evolutionary stage morphology and intestinal enzymatic activity in which most regions can produce all the enzymes (Cyrino et al. 2010). The gastrointestinal system of necessary to the digestive process. The activity of omnivores exhibit an adaptive variation due to the enzymes is affected by the intestinal pH, in some different eating haBits. The alimentary canal begins cases; the pH change can affect 50% of the activity at the mouth and ends in the anal opening, it may Be of an enzyme (Deguara et al. 2003). Several studies Pan-American Journal of Aquatic Sciences (2017), 12(3): 254-258 Gastrointestinal pH: Piaractus mesopotamicus 255 have been carried out with the objective of knowing the tissue, using a Metrohm 632 pH meter, with a pH the intestinal morphometry of the fish and the time probe InLab® Micro. of gastrointestinal transit (Montagne et al. 2003; For the statistical analysis, the data were Fabregat et al. 2011; Dias-Koberstein et al. 2005; subjected to normality verification through the Rodrigues et al. 2010), but there is little information Kolmogorov-smirnov & Liliefors test and to relating the intestinal pH during fasting and the homogeneity through Levene’s test. When those two changes that occur after feeding. Stomach and requirements were accomplished, ANOVA was intestinal pH undergoes variations according to applied followed by Tukey’s test (α = 0.05). feeding conditions or fasting. The reduction of pH in The variation of pH in the gastrointestinal the stomach and feed depends largely on the tract of pacu was more evident in the stomach than buffering capacity of the feed ingredients (Freitag in the other intestinal portions evaluated (Fig. 2). 2007). Thus, the objective of this study was to The pH of the stomach showed statistical evaluate the difference in pH along the digestive differences (p<0.05), with a range of 1.47 to 5.12 tract of pacu (P. mesopotamicus) to support future during the evaluation, the lowest value observed in nutrition studies on the species. the stomach was 1.18 before feeding. The portions The experiment was conducted with 24 of the anterior intestine and medium intestine juvenile of P. mesopotamicus with an average showed no significant changes (p<0.05) in any weight of 125.0 ± 5.7 g and a total length of 17.2 ± evaluation with pH means ranging from 7.09 to 8.13. 2.3 cm. Juveniles were also separated into six net The third portion of the posterior intestine showed pen, totaling four fish per experimental unit. The statistical differences (p<0.05) among the times (Fig. fishes were maintained under natural photoperiod. 2). An increase in pH was observed after feeding, For the evaluation of gastric and intestinal pH, from 7.65 to 8.07 decreasing after 4 hours until the six different times were used, the first evaluation end of the evaluations, which showed pH of 7.22. was performed with the animals starved, with the It was observed that after the fish were fed the fish fasted for 24 hours prior to study initiation. stomach pH increased significantly, thus suggesting After checking the pH in fasting, fishes were feed the influence of the feed buffering power over the with a commercial diet containing 28% CP and 3000 gastric pH (Maier & Tulles 1984). This feed Kcal/kg-1. The pH was measured before feeding, buffering capacity was observed in other studies as during feeding and at four equal intervals of two Deguara et al. (2003) using Sparus aurata, with pH hours (2, 4, 6 and 8 hours after delivery of food). average decreasing of 5.50 to 2.50 in the stomach In each evaluation, fishes were euthanized by portion and values of 6.95 to 7.90 in the anterior and an overdose of eugenol 400 mg.L-1 according to the posterior portions. Yufera et al. (2012) described for methodology proposed by Rotili et al. (2012) juvenile Diplodus sargus, the stomach pH range (methodology approved by the committee of ethics variation of 7.00 to 3.00 for approximately 8 hours in the use of animals – CEUA-UFPR) then they after feeding. Remote studies reported fast pH were carefully eviscerated in order to maintain the reduction in the stomach of some fish species like gastrointestinal tract intact, the stomach was then Lepomis macrochirus (Norms et al. 1973), separated from the intestine, after that the intestine Oreochromis niloticus (Moriarty 1973) and was divided into three equal portions (Fig. 1). Oreochromis mossambicus (Maier & Tullis 1984). The low stomach pH emulsifies the lipids, denature proteins and carbohydrates, and facilitates the action of digestive enzymes, causing the release of free amino acids present in the food (Bowen 1980, NRC 2011). Chakrabarti et al. (1995) observed in a broad study assessing digestive enzymes of 11 freshwater fish species, where the pH was measured with Figure 1. Gastrointestinal system of pacu: A - Stomach; B satiated fish presented variations among 5.32 to 7.02 - Anterior intestine; C - Medium intestine; D - Posterior for the stomach, from 5.74 to 8.02 for anterior intestine. portion of 5.60 to 8.10 for the medium portion and 5.41 to 7.89 for posterior portion, similar pH values The pH of each gastrointestinal tract sections were observed in this study when the fishes were was measured individually in triplicates directly in fed. Pan-American Journal of Aquatic Sciences (2017), 12(3): 254-258 256 W. GONÇALVES-FRANÇA ET AL. 1 0 B efore feeding 9 D uring feeding 2 h o u r s a a 8 4 h o u r s a B a B B 6 h o u r s B 7 8 h o u r s 6 e u a l a a a B v 5 H a B p 4 a B 3 2 B 1 0 S t o m a c h A nterio r intestine M edium intestine P osterio r intestine A reas of the digestive tract Figure 2. Comparison of pH on the digestive tract pacu P. mesopotamicus over time. The pH changes in the stomach can be mesopotamicus at different times. Therefore, we can explained by normal digestive processes, so the conclude that the pH has a greater variation in the decrease in pH occurs as digestive enzymes are stomach, especially at the moment of feeding where secreted in response to the food present in the the pH tends to become less acid due to food intake. stomach (Deguara et al. 2003). According to Prosser This was already expected since the low amount of (1973) and Guyton (1981) food in the stomach is gastric enzyme tends to Be neutralized by the feed known to stimulate gastric acid secretion, a mixture which presents pH close to the neutral, requesting of acid and enzyme, justifying the changes in the greater release of gastric enzymes in the stomach to stomach pH values observed in this study. break down and digest the alimentary particles, as it According to Wilson et al. (2002), Grosell et is observed with the increase of the pH two hours al.