The objective of the current study was to evaluate the effect of dietary siam weed (Chromolaena odorata) leaf extract on growth, feed utilization, proximate composition and stress resistance in Nile tilapia (Oreochromis niloticus).
Fingerlings (~3.5 g initial weight) were fed 4 experimental diets with different levels of siam weed extract; 0 g/kg (SW0, control), 1 g/kg (SW1), 2 g/kg (SW2) and 3 g/kg (SW3) in triplicates for 8 weeks. After 8 weeks feeding trial, 14 fish from each tank were subjected to thermal stress, 7 for high temperature and 7 for low temperature. Water temperature was gradually increased from 28º C to 34±1º C and/or decreased from 28º C to 18±1º C, respectively over a 1-week period. Fish were fed for another 2 weeks at high (34º C) or low (18º C) temperatures.
At the end of the 8-week feeding trial, fish increased their initial body weigh 4 – 4.4 fold depending on the experimental groups. Final weight, %weight gain, specific growth rate (SGR) and feed conversion ratio were not significantly influenced by the dietary treatments averaging 14.6 g, 311.6%, 2.5 and 1.3. However, growth performance dramatically decreased at high (2.2 fold lower SGR) and low (4.5 fold lower SGR) temperatures compared to those raised at optimal temperature. High temperature exposure caused a higher MDA level when fish fed control and SW1 diets in comparison to those fed SW2 and SW3 diets. In fish fed SW2 diet when exposed to high temperature MDA level was similar with those on control diet but significantly higher in comparison to those exposed to low temperature. Fish on the highest level of dietary siam weed extract (SW3 diet) had similar MDA levels for all temperatures. Serum cortisol level was significantly influenced by temperature, temperature × siam weed extract interaction (P<0.05), but not by the dietary siam weed level. Cortisol level tended to increase with both high and low temperatures compared to the optimal temperature (Fig. 1). However, fish fed the diet with the highest siam weed extract (SW3; 3 g/kg) at 34 °C had similar serum cortisol level with those fed at optimal temperature (28 °C).
Dietary siam weed extract did not influence growth; however, lowered oxidative stress at high temperature when provided at 2 – 3 mg/kg level, and physiological stress when provided at 3 g/kg level. Further dose-dependent studies need to disclose the impact of dietary siam weed extract on growth and welfare in Nile tilapia.