Dietary electrolyte balance affects the nutrient digestibility and maintenance energy expenditure of Nile tilapia

Abstract

Acid -base disturbances caused by environmental factors and physiological events including feeding have been well documented in several fish species, but little is known about the impact of dietary electrolyte balance (dEB). In the present study, we investigated the effect of feeding diets differing in dEB (2100, 200, 500 or 800 mEq/kg diet) on the growth, nutrient digestibility and energy balance of Nile tilapia. After 5 weeks on the test diet, the growth of the fish was linearly affected by the dEB levels (P, 0·001), with the lowest growth being observed in the fish fed the 800 dEB diet. The apparent digestibility coefficient (ADC) of fat was unaffected by dEB, whereas the ADC of DM and protein were curvilinearly related to the dEB levels, being lowest and highest in the 200 and 800 dEB diets, respectively. Stomach chyme pH at 3 h after feeding was linearly related to the dEB levels (P,0·05). At the same time, blood pH of the heart (P,0·05) and caudal vein (P,0·01) was curvilinearly related to the dEB levels, suggesting the influence of dEB on postprandial metabolic alkalosis. Consequently, maintenance energy expenditure (MEm) was curvilinearly related to the dEB levels (P,0·001), being 54 % higher in the 800 dEB group (88 kJ/kg 0·8 per d) than in the 200 dEB group (57 kJ/kg 0·8 per d). These results suggest that varying dEB levels in a diet have both positive and negative effects on fish. On the one hand, they improve nutrient digestibility; on the other hand, they challenge the acid -base homeostasis (pH) of fish, causing an increase in MEm, and thereby reduce the energy required for growth.

Cell wall disruption: An effective strategy to improve the nutritive quality of microalgae in African catfish ( Clarias gariepinus )

“…Hlophe et al () show that tilapia through their intestinal microflora has more capacity to produce endogenous cellulase than catfish before feeding. In addition, the low pH conditions in Nile tilapia (which can reach pH 2 at 7 hr after feeding) (Saravanan et al, ) are more suited to digest plant materials than African catfish (pH 3.5 at 8 hr after feeding) (Hlophe et al, ). Therefore, the marginal increase in nutrient ADCs for all the microalgae in Nile tilapia compared to African catfish could be attributed to the combined effects of endogenous cellulase production and low pH conditions in the digestive tract.…”

Feeds, water quality, gut morphology and digestion in Nile tilapia (Oreochromis niloticus)

“…The intestine was divided in three regions: proximal (from the pyloric part of the stomach to the spiral part of the intestine), middle (the spiral part of the intestine), and distal (from end spiral part of the intestine to 2 cm before the anus) (Pirarat et al, 2011). The gastro-intestinal pH was measured by pooling the digestive liquid of each section for all three fishes within each replicate of treatment, using a digital pH meter (Trans pH Model HP4030, DTK Water) as described by Amirkolaie et al, (2006) and Saravanan et al, (2013). For intestinal histology, one-cm portion of each of the three intestinal segments were fixed by immersion in Bouin's fixative solution.…”

Tissue pH and gut ecomorphology in six freshwater teleostsoccupying different trophic levels

“…In freshwater teleosts, in particular Cyprinidae, available information on GI tract pH is extremely scant and knowledge gaps exist (Bitterlich, 1985;Chakrabarti et al, 1995). Blood pH constitutes one of the most important biological features, but few studies have been conducted on this aspect in fish (Saravanan et al, 2013). Of the fish species studied, the blood pH characteristics were recorded in this study.…”

“…Direct involvement of GI tract pH in the partitioning of bivalent ions has been shown in rainbow trout stomach (Bucking and Wood, 2009). In turn, the characteristics of GI and blood pH are influenced by diet and altered dietary electrolyte balance (Saravanan et al, 2013). Thus, condition-specific findings for these characteristics in a given species, to some degree, cannot be extrapolated directly to others, and specific validation studies for different species are needed.…”

“…The overriding blood pH changes are subjected to external and internal challenges (Sugiura et al, 2006). The blood pH recorded from fish in previous studies also showed a wide range from 7.38 to 8.1 (Cooper and Wilson, 2008;Saravanan et al, 2013).…”