Osmo-regulation requires energy.An increased effort for osmo-regulation is often suggested to reduce growth by an increased energy requirement for maintenance.Although not consistent, several studies report an increase in growth if salt is supplemented to diets,but it is not clear if this is due to an increased feed intake or an altered maintenance requirement.In contrast,a recent study in Nile tilapia(Oreochromis niloticus) on estimating net-energy from digestible macronutrient intake,found a negative relation between digestible ash intake and energy retention. This suggests an increase in energy requirements for maintenance.Therefore,this study assessed the impact of dietary salt supplementation(4%) on energy balances and nutrient digestibility in Nile tilapia.Ten groups of each 25 fish(initial weight 139g) were assigned to one of two diets:a control diet(96%basal mixture and 4%cellulose) and a test diet supplemented with 4%NaCl (96%basal mixture and 4%NaCl).Fish were fed restrictively at 80%of their assumed satiation feeding level,during a 36-d experimental period.Energy and nitrogen balances were measured by the slaughter method for estimating the energy requirements for maintenance assuming that the efficiency of energy utilization for growth was equal for both diets.Apparent nutrient digestibilities(ADC) were corrected for the supplemented NaCl(assumed 100%digestible) and cellulose(assumed to be indigestible).ADC of ash,energy and fat were similar for both diets. ADC of crude protein and carbohydrates(i.e.,NFE) were slightly lower with the NaCl-supplemented diet(P0.05).Nitrogen retention was similar at both diets(P0.10) despite the fact the digestible nitrogen intake was higher with the control than with the NaCl diet (P0.001).Partitioning of energy was affected by NaCl supplementation.The 1.7%lower metabolizable energy intake(P0.01) together with a 3.9%higher heat production(P0.05) lead to a 10.3%lower energy retention(P0.001) at the NaCl-diet compared to the control.Since nitrogen retention was equal at both diets,the differences in energy retention was fully due to a difference in the amount of energy deposited as fat(P0.001).The estimated energy requirements for maintenance were 15%higher at the NaCl-diet compared to the control diet(P0.01).In conclusion,dietary NaCl supplementation in Nile tilapia does not improve energy partitioning, since it increases maintenance and reduces digestibility of some nutrients.It is hypothesized that dietary NaCl,disturbs osmo-regulation in the intestine,hampering digestion and increasing maintenance.
|Title of host publication||The 14th International Symposium on Fish Nutrition and Feeding: Program & Abstracts. May 31-June 4, 2010, Qingdao, China|
|Place of Publication||Qingdao, China|
|Publication status||Published - 2010|
|Event||The 14th International Symposium on Fish Nutrition and Feeding. May 31-June 4, 2010, Qingdao, China - |
Duration: 31 May 2010 → 4 Jun 2010
|Conference||The 14th International Symposium on Fish Nutrition and Feeding. May 31-June 4, 2010, Qingdao, China|
|Period||31/05/10 → 4/06/10|