Global production of farmed tilapia in at least 85 countries exceeded 3 million t in 2009 and requires high-quality fish feeds. In such intensive aquaculture production, bacterial diseases have been identified as a major cause of economic loss to producers. Feeding antibiotic-medicated feeds is a common practice to treat bacterial infections. Prophylactic use of antibiotics as growth promoters in aquaculture production has also occurred widely. However, growing awareness from consumers and producers of aquaculture species has resulted in a demand for responsible and sustainable aquaculture. Regulatory authorities in most exporting countries now focus on the misuse of antibiotic growth promoters (AGP) in aquaculture, while public attention has shifted towards sustainable production methods. Thus, alternative additives to replace AGP’s, which have been banned in EU animal feeds since 2006, have had to be tested. Dietary organic acids, and especially potassium diformate – the most widely tested organic acid salt in aquaculture, are among the various alternatives spearheading environmental friendly and nutritive-sustainable aquaculture approaches.
Dietary potassium diformate (KDF) has been tested in tilapia aquaculture since 2005 and since then numerous publications and conference contributions on the use of KDF in juvenile tilapia have been published from Europe, America and Asia. This study analyzed the average impact of the additive from all published studies on its effect on performance parameters such as weight gain, feed efficiency and mortality.
The final data-set contained the results of 8 published studies, comprising 18 trials with KDF-inclusion, which ranged from 0.2% to 0.75% and covered 3040 fish. Data were subjected to statistical analysis and a significance level of 0.05 was used in all tests. Results are expressed as percentage difference from the negatively controlled fish.
The average level of dietary potassium diformate from the data-set in all treated fish was 0.41%. Only a numerical increase of feed intake (2.1%) could be monitored (P=0.16) compared to fish without the additive. However, the performance of tilapia, based on final weight was significantly increased by 5.6% (P=0.009). Furthermore, the feed conversion ratio of fish fed KDF was also significantly improved (P=0.012): this time the improvement was 4.5%. Data on mortality were inconclusive, since some of the trials were carried out under clean laboratory conditions, while others employed a challenge with potentially pathogenic bacteria, such as Vibrio anguillarum, Streptococcus agalactiae, Streptococcus iniae and Aeromonas hydrophila. In these cases, dietary KDF, ranging from 0.2% till 0.5% reduced mortality (P<0.05) when employed against V. anguillarum; it tended to reduce (dosages between 0.2-0.6%) mortality caused by S. agalactiae and A. hydrophila, while it had no effect (KDF ranging from 0.25-0.75%) on mortality caused by S. iniae.
Table 1: Effects of potassium diformate in tilapia diets against negative control performance (responses as per cent of negative control) – data-set consists of 8 published studies covering 3040 fish
In general, results show significantly improved growth and FCR in tilapia fed with dietary potassium diformate, while its beneficial impact against pathogenic bacteria seem to be bacterial-challenge dependent. If calculated as fish productivity index, which is a function of weight gain, survival and FCR (Lückstädt & Kühlmann, 2011), the improvement extended to almost 17% (P=0.020). The use of KDF in tilapia feeding is therefore supported as a promising alternative in the contemporary aqua-feed industry in order to contribute to an ecologically sustainable tilapia production.
This paper was presented at the XV International Symposium on Fish Nutrition and Feeding Molde, Norway • 4-7 June 2012.