Sodium Diformate on the Growth Performance of Male Nile Tilapia

Introduction

Although antibiotic growth promoters in the diets of fish may promote growth and improve feed conversion and survival rates, public concern over cross-resistance to humans led to a ban on the use of such substances in the EU. Research has thus turned to other feed additives to maintain performance and high survival rates in aquaculture. Organic acids and their salts are seen as an alternative to using antibiotics as growth promoters (Lückstädt (2006), but their use in aquaculture is comparatively new compared to livestock and poultry feeds. Research in Atlantic salmon Salmo salar showed the beneficial effect of potassium diformate (KDF) on performance parameters (Christiansen and Lückstädt, 2008). Studies with hybrid tilapia have shown that fish given 0.3 and 0.6% KDF had significantly better growth than those given antibiotics (Zhou et al, 2009). This was confirmed by Cuvin-Aralar et al. (2010) who showed significantly better growth, growth rate and FCR in juvenile Nile tilapia given diets supplemented with 0.3% KDF compared to control diets. Limited data are available as to the effect of sodium diformate (NDF) on growth and FCR in Nile tilapia.

Material and methods

Twenty-five male Nile tilapia (mean weight 16.5 ± 3.2 g) were stocked in each of eight 240 l polyethylene tanks in a static-renewal system. The fish in four randomly selected tanks were given commercially formulated feed (CON) while the others received commercially formulated diets supplemented with 0.3% sodium diformate (NDF). Fish in both the CONTROL and NDF treatment were fed a daily ration equivalent to 5% of their body weight for the first two weeks; reduced to 3% until the sixth week and 2% until the end of the feeding trial. Feed was dispensed three times a day at 0800, 1200, 1600h. The fish were weighed every week to monitor growth and adjust feed ration. Eighty percent of the water was changed every 3 days, an hour after the morning ration was dispensed. Water quality (dissolved oxygen, temperature, pH and ammonia) was monitored prior to water replacement. The experimental ran for 78 days. Analysis of Variance using SAS (Cary, NC, USA) was used for statistical analyses with P<0.05.

Results

Water quality parameters were within the acceptable range for Nile tilapia growth. Mean dissolved oxygen was 6.1±0.4 mg l^-1, temperature was 29.1±3.5, pH was 6.7±0.9 and ammonia (NH₃-N) was <0.02. Effect of the treatment with the dietary acidifier on the growth of Nile tilapia was visible throughout the trial period. Nile tilapia fed NDF clearly tended to grow better compared to the CONTROL. ANOVA comparison of the mean weights achieved by the two groups on the final day of the experiment (day 78) showed a P-value of 0.055. Nile tilapia given the NDF supplement had higher mean weights (66.20±4.15g) compared to those given the CONTROL feed (58.74±4.71g). Specific growth rates (SGR) tended to be better in fish fed the NDF-supplemented diet (2.73±0.08) compared to controls (2.58±0.11) at the end of the experiment (P=0.057). Only numerical differences in survival of the fish in both groups were observed, but the bulk weight of fish in the NDF-fed group was significantly higher (1621±73g) compared to controls (1396±152g; P=0.038). Final feed conversion ratio (FCR) was significantly improved for the tilapia fed the NDF diet. FCR was 0.69±0.05 for the tilapia fed NDF supplemented feed, compared to 0.77±0.02 for the control group. Finally, the Fish Productivity Index FPI was significantly increased due to inclusion of NDF (Table I).

Table I: Production parameters of Nile tilapia after 78 days of rearing with or without sodium diformate

Parameter	CON	0.3% NDF	P-value
Initial weight [g]	16.5±3.2	16.5±3.2	-
Final weight [g]	58.7±4.7	66.2±4.2	0.06
Survival [%]	95.0±5.0	98.0±2.3	0.32
Bulk weight [g]	1396±152^b	1621±73^a	0.04
SGR* [%]	2.58±0.11	2.73±0.08	0.06
FCR	0.77±0.02^a	0.69±0.05^b	0.02
FPI**	525±98^b	708±54^a	0.02

^{a, b}: Means with a different superscript differ significantly at P<0.05

*SGR = Specific Growth Rate: (ln Final weight [g] - ln Initial weight [g]) / culture period [d] × 100

**FPI = Fish Productivity Index: Weight gain [g] × Survival [%] / (FCR × 10)

Discussion

Addition of 0.3% NDF in the diets of Nile tilapia improved growth and other production parameters significantly. These findings are in line with several other studies testing the effect of diformates in tilapia (Zhou et al, 2009; Cuvin-Aralar et al, 2010). To date, there has been only speculation on the mode of action of organic acid compounds in fish. Liebert et al. (2010) reported improved digestibility, especially of protein. Ng et al. (2009) found significantly reduced fecal bacteria counts in organic acid supplemented fish and similar trends were also observed in gut microflora. These may be among the reasons for improved growth. In terrestrial animals, reduced energy use from the gut microflora has energy sparing effects of up to 6% of the dietary net energy (Jensen, 1998). Organic acids, and especially sodium diformate, are therefore an interesting option to improve performance in tilapia.

References

Christiansen, R. and C. Lückstädt. 2008. Effects of different dosages of potassium diformate in fishmeal on the performance of Atlantic salmon Salmo salar. World Aquaculture Society Conference, Busan, Korea. Abstract-CD-Rom, p. 467.

Cuvin-Aralar M., K.-J. Kühlmann, K. Schroeder and C. Lückstädt. Effect of potassium diformate (KDF) on growth performance of male Nile tilapia (Oreochromis niloticus). XIV International Symposium on Fish Nutrition and Feeding, Qingdao, China, Book of Abstracts, p. 187.

Liebert F., K. Mohamed and C. Lückstädt. Effects of diformates on growth and feed utilization of all male Nile Tilapia fingerlings (Oreochromis niloticus) reared in tank culture. XIV International Symposium on Fish Nutrition and Feeding, Qingdao, China, Book of Abstracts, p. 190.

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Zhou Z., Y. Liu, S. He, P. Shi, X. Gao, B. Yao and E. Ringø. 2009. Effects of dietary potassium diformate (KDF) on growth performance, feed conversion and intestinal bacterial community of hybrid tilapia (Oreochromis niloticus x O. aureus). Aquaculture 291:89-94.