INVESTIGATION OF THE SUITABILITY OF INSECT MEALS AS PROTEIN SOURCES FOR RAINBOW TROUT

In recent years, interest has grown among fish culturists for cost effective and sustainable alternative protein sources to fish meal. As a part of the natural diets of salmonid, insects could provide a promising protein source in prepared feeds. A digestibility trial was conducted to determine the apparent digestibility coefficients (ADCs) of key nutrients in insect meals in order to evaluate their suitability as alternative protein sources for rainbow trout feeds.

Fish were fed either a reference diet or one of five test diets created by blending the reference diet with each of the test ingredients (Menhaden fishmeal (MFM), two cricket meals (A and B), waxworm meal, and mealworm meal)  in a 70:30 ratio (dry-weight basis).  Twenty-five, 370-g Rainbow Trout were stocked per 140-L poly tanks (N= 3/diet), with water temperature maintained at 15°C, and hand-fed twice daily to satiation one week prior to collection of fecal samples.  Fecal samples were collected by manual striping, freeze dried and three collections pooled per replicate tank.

Cricket meals A and B contained similar crude protein (CP) and lipid (CL) levels (68 and 69% CP and 17.1 and 16.6 CL%, respectively).  Mealworm meal contained 56.5% CP and 27.7% CL and waxworm meal contained 32.5% CP and 54.2% CL.

The apparent digestibility coefficients (ADCs) of dry matter (DM), CL, CP, gross energy (GE), and phosphorus (P) are shown in the figure. The protein ADCs were 81.6% for Cricket A and 79.5% for Cricket B; the latter of which was significantly lower than MFM (87%, P<0.05). The protein ADC for mealworm meal was 83.5% and waxworm meal was 82.8%. Both cricket meals A and B had significantly lower lipid ADCs (88.5% and 90.6%, respectively) than MFM (100%, P<0.05). The lipid ADC for mealworm meal was 93.5% and waxworm meal was 96.1%.