Apparent digestibility coefficients of selected protein ingredients for pirarucu Arapaima gigas (Teleostei: Osteoglo ssidae)

Abstract

Apparent digestibility coefficients (ADCs) of nine protein ingredients were determined for pirarucu Arapaima gigas, a Neotropical fish species with great aquaculture potential in the Amazon. ADCs of crude protein, energy and dry matter were determined by feces sedimentation in cylindrical-conical tanks. Experimental diets were composed of 795 g kg-1 of the reference diet, 5 g kg-1 of chromic oxide and 200 g kg-1 of the following test ingredients: fish by-product meal, salmon by-product meal, poultry by-product meal, hydrolyzed feather meal, meat and bone meal, blood meal, soybean meal, corn gluten meal and corn gluten feed. Blood meal, meat and bone meal and corn gluten feed resulted in low ADCs for pirarucu, whereas corn gluten meal, poultry by-product meal and soybean meal were better digested, indicating that these ingredients may be potential protein sources in feed formulations for pirarucu. The other animal protein ingredients presented intermediate ADCs values and, together with blood meal and meat and bone meal, they demonstrate that the nutritional quality of the animal by-products tested could be improved, especially by enhancing the processing methods of this group of ingredients.

Optimizing methodological aspects of stool collection by sedimentation in digestibility studies with pirarucu ( Arapaima gigas )

“…Floating stool has already been described in another digestibility test with pirarucu (Rodrigues et al, 2019). The pirarucu rectum has a high concentration of goblet cells that have the function of protecting the mucosa in the rectum and lubricating the faeces (Rodrigues & Cargnin‐Ferreira, 2017).…”

“…As with the reference and corn diets, the stool of fish fed the soybean meal visually acquired greater consistency from days 5 to 10 with the diet; however, in comparison with the other diets, they presented a less consistent and more fragmented pattern on day 10. Less consistent and more liquid stools were described by Rodrigues et al (2019) when assessing the digestibility of soybean meal for juvenile pirarucu, which was also reported for Atlantic salmon ( Salmo salar ) (Kraugerud et al, 2007; Refstie et al, 1999). Studies evaluating the inclusion of soybean meal in fish diets commonly report the occurrence of morphological changes and intestinal inflammation associated with reduced nutrient digestibility and performance.…”

“…Two test ingredients were evaluated, one to provide energy (corn) and the other to provide protein (soybean meal). Each test diet was composed of 795 g kg −1 of the reference diet, 200 g kg −1 of the test ingredient and 5 g kg −1 of chromium oxide III (Table 1) (Rodrigues et al, 2019). The 80:20 proportions of the experimental diets were defined based on the carnivorous feeding habit of the species to ensure that it reflected the reference diet and to avoid the test ingredients adversely affecting intake of the diet (Glencross et al, 2007; National Research Council (NRC), 2011).…”

“…Digestibility studies detailing ingredients to be fed to pirarucu have recently been published. Great variation regarding the period of acclimatization to experimental diets was observed, such as three (Santos‐Cipriano et al, 2015), four (Cipriano et al, 2016), five (Rodrigues et al, 2019) and 15 days (Ramos et al, not published). Stool collection for digestibility tests with pirarucu conducted in the authors' laboratory was quite laborious due to some peculiarities of the species, since in addition to defecating soon after eating, some part of the faeces produced first floats in the water, sedimenting only a few minutes later.…”

“…Stool collection for digestibility tests with pirarucu conducted in the authors' laboratory was quite laborious due to some peculiarities of the species, since in addition to defecating soon after eating, some part of the faeces produced first floats in the water, sedimenting only a few minutes later. The samples were collected immediately after being visualized in the collection tubes or on the water surface to avoid nutrient leaching into the water as well as due to the lack of information concerning how long the faeces remain in the water before collection (Rodrigues et al, 2019), which requires excessive manpower. To standardize and optimize the sediment collection methodology used in digestibility studies with pirarucu, this study evaluated (i) the gastrointestinal transit time (GITT); (ii) the period of acclimatization to experimental diets and (iii) the maximum period that stool can remain in the collection tubes without nutrient leaching.…”