Research Article |
Corresponding author: Bernardo Baldisserotto ( bbaldisserotto@hotmail.com ) Academic editor: Carolina Arruda Freire
© 2018 Ana Paula Gottlieb Almeida, Everton Luis Zardo, Candida Toni, Everton Rodolfo Behr, Leila Picolli da Silva, João Paes Vieira, Vania Lúcia Loro, Bernardo Baldisserotto.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Gottlieb Almeida AP, Zardo EL, Toni C, Behr ER, Picolli da Silva L, Vieira JP, Loro VL, Baldisserotto B (2018) Composition of gastrointestinal content, protease and lipase activities in summer and winter of four freshwater siluriforms (Teleostei: Actinopterygii) with two different feeding habits. Zoologia 35: 1-8. https://doi.org/10.3897/zoologia.35.e13286
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The aim of this study was to determine the composition of gastrointestinal content and protease and lipase activities in summer and winter as well as to evaluate the relationship between digestive enzyme activity and centesimal composition of gastrointestinal content and feeding habits of two omnivorous species, Rhamdia quelen (Quoy & Gaimard, 1824) and Pimelodus maculatus (LaCèpede, 1803), and of two detritivorous species, Loricariichthys anus (Valenciennes, 1835) and Hypostomus commersoni (Valenciennes, 1836). The activities of pepsin, trypsin, chymotrypsin, and lipase, and the levels of proteins and lipids in the gastrointestinal tract, were evaluated. The enzyme activities were not related to the centesimal composition of gastrointestinal content or feeding habits. This finding could be associated with the variations of nutrient availability over time in the environment, as was observed in the centesimal composition of food ingested by the fish in summer and winter. The analyzed enzymes exhibited a constitutive character in these species; that is, the digestive enzymes are always available in the gastrointestinal tract to digest any food that the fish may find as an adaptation to better utilize the nutrients available in the environment in winter and summer.
Chymotrypsin, fish, lipase, pepsin, trypsin
The digestive enzymes in vertebrates are synthetized and secreted throughout the gastrointestinal tract. Fish have a high versatility in their digestive processes, which may vary according to species, size, age, stage of maturity, temperature, type of food ingested and feeding history. The appropriate synthesis and levels of digestive enzymes may be affected by environmental factors that vary over time (
Fish are usually classified according to feeding habits, and it is expected that digestive enzyme activities reflect the feeding habits and the diet of the fish (
Understanding the relationship between digestive enzyme activities and centesimal composition of the ingested food by the fish in the environment is important to the comprehension of the feeding biology of species. In addition, previous studies of fish collected in the environment analyzed only the activities of digestive enzymes without evaluating the centesimal composition of ingested food. Four teleost species belonging to two trophic guilds, omnivorous and detritivorous, were chosen for this study. The omnivorous Rhamdia quelen (Quoy & Gaimard, 1824) (Heptapteridae) (jundiá) feeds mainly on fish, crustaceans, insects, plant remains, and organic detritus (
Adults of four fish species: R. quelen (40.7 ± 0.6 cm, 779.3 ± 73.4 g, voucher number: 16-1901) (Fig.
Samples from the stomach, anterior intestine, and posterior intestine were homogenized in an ice bath (wet weight 0.05 g: 1 mL homogenization buffer) with an Ultraturrax. The homogenization buffer solution was 20 mM Tris and 10 mM phosphate, pH 7.0 in 50% (v/v) glycerin. The extract was centrifuged (1000 g; 4 °C; 5 min) and the supernatant was utilized in assays as an enzyme source (
Pepsin activity was assayed by the specific methods of
Lipase activity was assayed by the specific method of
To establish the specific activities of the enzymes, protein concentrations were determined in the enzyme extracts by the methods of
Protein and lipid concentrations were determined in the stomach and intestinal contents. The protein concentration was determined according to the micro Kjeldahl method (method 920.52) according to
Data are presented as the mean ± S.E.M. Levene’s test was used to verify the homogeneity of variance. If the data were homoscedastic, comparisons between digestive enzymatic activities were assessed by two-way ANOVA (species vs. seasons) followed by Tukey’s test. The conditions for parametric ANOVA were not satisfied in the activities of pepsin and trypsin in the posterior intestine; thus, the non-parametric Scheirer-Ray-Hare extension of the Kruskal-Wallis test was used, followed by the Nemenyi test (
The highest pepsin activity rate per mg protein was detected in the stomach of the omnivorous species (R. quelen and P. maculatus) in both seasons, and for both species, the higher activity of this enzyme occurred in the winter (Fig.
The highest chymotrypsin activity rate per mg protein in the anterior intestine in the summer was detected in H. commersoni followed by R. quelen. On the other hand, in the winter, the highest activity rate per milligram protein was observed in P. maculatus, followed by L. anus. The activity of this enzyme in the anterior intestine of P. maculatus and L. anus was higher in the winter than in the summer, but the opposite was observed for the other two species (Fig.
The lipase activity rate per mg protein was highest in the anterior intestine of H. commersoni and R. quelen in summer. In the winter, the highest lipase activity rate per mg protein was found in P. maculatus followed by L. anus. The activity of this enzyme in the anterior intestine of P. maculatus and L. anus was higher in the winter than in the summer, but the opposite was observed for the other two species (Fig.
Proteolytic enzymatic activities in the omnivorous R. quelen and P. maculatus and detritivorous L. anus and H. commersoni in the summer and winter: (5) pepsin in the stomach; (6) trypsin in the anterior intestine; (7) trypsin in the posterior intestine; (8) chymotrypsin in the anterior intestine; (9) chymotrypsin in the posterior intestine. Different letters indicate significant differences between species in the same season. * Indicates a significant difference from summer in the same segment (p < 0.05). (U, a Caraway unit) (n = 15 from each species at each season).
Lipase activity in the omnivorous R. quelen and P. maculatus and detritivorous L. anus and H. commersoni in the summer and winter: (10) anterior intestine; (11) posterior intestine. Different letters indicate significant differences between species in the same season. * Indicates a significant difference from the summer in the same segment (p < 0.05). (U, a Caraway unit) (n = 15 from each species at each season).
The H. commersoni specimens collected did not have any content in the stomach in either season, whereas L. anus exhibited stomach and intestinal contents in the summer, but not in the winter. Rhamdia quelen and P. maculatus presented stomach and intestinal content in both seasons.
The highest protein concentration in the stomach content in the summer was found in R. quelen. In the winter, the highest protein concentration was found in P. maculatus. Rhamdia quelen presented a higher protein concentration in the stomach content in the summer, but for P. maculatus, this concentration was higher in the winter. In the anterior intestinal content, the highest protein concentration in the summer was found in H. commersoni. In the winter, this species showed a comparatively lower protein concentration than in the summer, and the highest concentrations were observed in R. quelen and P. maculatus. The highest protein concentration in the posterior intestinal content was found in R. quelen in both seasons. The protein concentration of the posterior intestinal content was higher in the winter than in the summer in P. maculatus, but the opposite was observed in R. quelen (Table
Percentage and range (between parentheses) of protein and lipids (dry matter) in the content of the gastrointestinal tract of four teleost species collected in two seasons.
Species | Stomach | Anterior intestine | Posterior intestine | |||
---|---|---|---|---|---|---|
Summer | Winter | Summer | Winter | Summer | Winter | |
Protein | ||||||
Rhamdia quelen | 61.77 ± 10.81ª | 18.37 ± 6.49ª* | 11.21 ± 0.03ª | 21.59 ± 12.69ª* | 52.92 ± 4.35ª | 25.87 ± 0.17ª* |
(50.95 – 72.58) | (11.89 – 24.86) | (11. 18 – 11.25) | (8.90 – 34.28) | (48.57 – 57.28) | (25.70 – 26.04) | |
Pimelodus maculatus | 9.05 ± 1.16b | 44.86 ± 0.65b* | 12.04 ± 0.95ª | 24.35 ± 8.54ª* | 9.45 ± 0.26b | 17.66 ± 1.41b* |
(7.89 – 10.205) | (44.21 – 45.51) | (11.09 – 12.99) | (15.81 – 32.89) | (9.19 – 9.72) | (16.26 – 19.07) | |
Loricariichthys anus | 11.04 ± 0.04b | N | 10.47 ± 0.19ª | N | 13.77 ± 1.45bc | N |
(10.99 – 11.08) | (10.28 – 10.66) | (12.31 – 15.22) | ||||
Hypostomus commersoni | N | N | 15.29 ± 2.94b | 9.57 ± 0.14b* | 7.05 ± 0.72c | 7.78 ± 3.01c |
(12.35 – 18.23) | (9.43 – 9.70) | (6.34 – 7.77) | (4.76 – 10.79) | |||
Lipids | ||||||
Rhamdia quelen | 7.07 ± 0.08ª | 0.91 ± 0.07ª* | 0.71 ± 0.09ª | 0.51 ± 0.22ª | 1.94 ± 0.23ª | 0.64 ± 0.07ª* |
(6.98 – 7.15) | (0.84 – 0.97) | (0.62 – 0.80) | (0.29 – 0.73) | (1.71 – 2.16) | (0.56 – 0.71) | |
Pimelodus maculatus | 0.41 ± 0.01b | 1.96 ± 0.29b* | 0.29 ± 0.02ª | 0.56 ± 0.15ª* | 0.27 ± 0.03ª | 1.67 ± 0.51ª* |
(0.39 – 0.42) | (1.68 – 2.25) | (0.27 – 0.31) | (0.41 – 0.71) | (0.24 – 0.29) | (1.15 – 2.18) | |
Loricariichthys anus | N | N | 0.75 ± 0.08ª | N | 2.34 ± 2.28ª | N |
(0.67 – 0.83) | (0.06 – 4.62) | |||||
Hypostomus commersoni | N | N | 4.81 ± 1.41b | 7.36 ± 0.82b | 3.82 ± 0.01b | 2.72 ± 1.34ª |
(3.40 – 6.22) | (6.54 – 8.17) | (3.81 – 3.83) | (0.52 – 3.83) |
The highest lipid concentration in the stomach content in summer was found in R. quelen; in the winter, the highest concentration was observed in P. maculatus. In the anterior intestinal content, the highest lipid concentration was found in H. commersoni in both seasons. In the posterior intestinal content, the highest lipid concentration in summer was found in H. commersoni. In the winter, there was no difference in lipid concentrations in the posterior intestinal content of all species that presented any content. The lipid concentrations in the stomach and posterior intestinal content were lower in the winter than in the summer in R. quelen, but for P. maculatus, the lipid concentrations in the content of the entire digestive tract were higher in the winter than in the summer (Table
There was no relationship between the enzyme activities and the centesimal composition of the different segments. It was not possible to determine the relationship between the digestive enzymatic activity and the centesimal composition of ingested food in the stomach of H. commersoni in both seasons due to the absence of stomach content. In winter, this relationship could not be determined in L. anus due to the absence of content in the three segments of the gastrointestinal tract used in this study.
Several studies on the activity of digestive enzymes in fish suggested that enzymatic activity is influenced by the diet ingested or by feeding habits (
In the present study, the protein and lipid concentrations observed in the gastrointestinal tract did not show any relationship with proteolytic and lipase activities. This absence can be associated with the variation of nutrient availability over time in the environment, as it was observed in the centesimal composition of food ingested by the fish in the summer and winter.
Pepsin was the only digestive enzyme that had higher activity in the omnivorous than in the detritivorous species analyzed in the present study, but protein concentrations in the stomach content were not related to the activity of this enzyme. Similar results were found by
Overlapping diets may occur in the wild, such as detritus in R. quelen and sand grains in P. maculatus (
In conclusion, the activity of pepsin in the stomach was higher in the omnivorous than in the detritivorous species, but the other studied digestive enzymes could not be used as indicators of feeding habits because this relationship is usually not found in fish collected in the wild.