Effects of low inclusion levels of dried drumstick tree Moringa oleifera leaves into the diets of rainbow trout, Oncorhynchus mykiss, on growth, feed conversion and some blood parameters

The drumstick tree, Moringa oleifera (MO), is a multi-purpose plant containing high amounts of plant secondary compounds like total phenolics, tannins, saponins and phytic acid.

Moringa leaves have been tested for various applications so far. They contain high amounts of protein (around 25% CP of untreated, whole, dried leaves in the dry matter), carotenoids, ascorbic acid and minerals and have been tested as fish meal replacement for Nile tilapia in several studies. Defatted MO seed meal has also been used as feed additive for sheep with indications of improved rumen fermentation. However, up to now, MO leaves have not been tested for their effects in carnivorous fish. Therefore an experiment was conducted in which rainbow trout, Oncorhynchus mykiss, were fed 0 (control, C), 0.625 (M 0.625), 1.25 (M 1.25), 2.5 (M 2.5) and 5% (M 5) of dried MO leaves in a fish meal based diet for a total duration of eight weeks. Each diet was fed to six replicate 55 l aquaria containing 25 fish each (mean initial body mass = 3.92 ± 0.08 g) in a flow-through system with approximately a 10-fold water exchange rate per day. Growth, feed conversion, fin index, blood glucose and hematocrit were evaluated for the five groups.

No differences were observed in any of the evaluated parameters. The fish grew between 428% (M 5) and 447% (M 0.625), the feed conversion ratios were between 0.95 (M 0.625) and 0.97 (M 5), the blood glucose levels were between 4.23 (M 1.25) and 4.42 (M 0.625), the hematocrit values were between 45.1 (M 2.5) and 50.7 (M 1.25) and the fin indices of dorsal and caudal fins were around 1 (Table 1). In conclusion, it can be said that even comparatively high levels of 5% untreated MO dried leaves in the diet had no negative impact on fish performance and can thus be utilized for aquaculture as potential protein source.

Tab. 1: Growth performance, feed conversion, blood glucose, hematocrit and fin index of the rainbow trout.

	c	M 0.625	M 1.25	M 2.5	M 5
Initial body mass (g)	3.92 ± 0.07	3.92 ± 0.09	3.89 ± 0.08	3.91 ± 0.08	3.98 ± 0.09
Final body mass (g)	17.0 ± 0.63	17.5 ± 0.99	17.0 ± 1.21	17.1 ± 0.87	17.0 ± 0.50
Growth (%)	435 ± 19.1	447 ± 30.2	437 ± 27.9	437 ± 16.9	428 ± 12.6
SGR (% day-1)	2.33 ± 0.07	2.37 ± 0.11	2.34 ± 0.10	2.34 ± 0.06	2.31 ± 0.05
Feed conversion ratio	0.96 ± 0.03	0.95 ± 0.05	0.96 ± 0.05	0.96 ± 0.03	0.97 ± 0.03
Blood glucose (mmol/l)	4.36 ± 0.18	4.42 ± 0.22	4.23 ± 0.34	4.39 ± 0.48	4.37 ± 0.31
Hematocrit	46.2 ± 2.57	48.2 ± 8.13	50.7 ± 5.61	45.1 ± 3.14	47.0 ± 0.62
Dorsal fin index	0.96 ± 0.10	0.81 ± 0.30	1.13 ± 0.21	0.92 ± 0.36	1.10 ± 0.23
Caudal fin index	0.88 ± 0.21	0.79 ± 0.16	0.88 ± 0.19	0.67 ± 0.20	0.79 ± 0.13
Values are expressed as mean ± SD, n = 6, SGR = specific growth rate