Radiolabelled DL-Met and MHA-Ca to elucidate the metabolic and nutritional response of two commercial methionine sources in Nile tilapia juveniles
The study demonstrated that DL-methionine (DLM) is a more efficient methionine source than methionine hydroxy analogue calcium salt (MHA-CA) for Nile tilapia, showing superior outcomes in growth, feed efficiency, nitrogen utilization, and body protein synthesis. The radiolabeled Met study further confirmed that MetAMINO® (DLM) is more effectively incorporated into body protein, namely the liver, viscera, muscle, head, heart, kidney, bones and fins, compared to the MHA product, whereas a greater proportion of MHA-Ca was catabolized and excreted into the water.
DLM is a more efficient methionine source than MHA for Nile tilapia, showing superior outcomes in growth, feed efficiency, nitrogen utilization, and body protein synthesis, while MHA-Ca showed higher catabolism, indicating less metabolic efficiency.
Aqua Expert and Regulatory Trial Manager Evonik Operations GmbH, Germany
Trial I – Performance response:
Evaluates how Met sources (DLM vs. MHA-Ca) affect growth performance, feed conversion and nitrogen utilization of Nile tilapia when supplemented on an equimolar basis
Trial II – Metabolic response:
Elucidates metabolic utilization of Met sources on the fish body protein synthesis based on ¹⁴C-labelled Met sources.
Location: Centre of Marine Sciences of Algarve (CCMAR), Portugal
Project team leaders: Karthik Masagounder1, Sofia Engrola2, Rita Teodósio2,3, Miguel Cabano2, Rita Colen2 and Cláudia Aragão2,3
1 Evonik Operations GmbH, Hanau‐Wolfgang, Germany
2 Centre of Marine Sciences (CCMAR), Faro, Portugal
3 Universidade do Algarve, Faro, Portugal
| Animals | Nile tilapia, 2.30 g initial body weight ; 50 fish per replicate tank |
| Design | 3 tanks (100 L) per diet; 50 fish per tank |
| Diets | Basal: Diet without supplemental Met DLM: Basal + 1.5 g/kg DL-Met MHA: Basal + 1.8 g/kg MHA-Ca (equal to DL-Met dose on a molar basis) |
| Feeding | Three times a day over a 57-days period |
| Parameters | Final body weight, total body weight gain of all fish (biomass gain) per tank, Feed conversion ratio (FCR), |
| Duration | 57 days |
Location: Centre of Marine Sciences of Algarve (CCMAR), Portugal
Project team leaders: Karthik Masagounder1, Sofia Engrola2, Rita Teodósio2,3, Miguel Cabano2, Rita Colen2 and Cláudia Aragão2,3
1 Evonik Operations GmbH, Hanau‐Wolfgang, Germany
2 Centre of Marine Sciences (CCMAR), Faro, Portugal
3 Universidade do Algarve, Faro, Portugal
| Animals | Nile tilapia, 25-28 g |
| Design | At end of 57-d feeding trial, 10 or 11 fish from each tank were transferred to individual metabolic chambers (2-L water) (n=31 fish for DLM; n=32 fish for MHA) |
| Diets | DLM: Basal + ¹⁴C-DL-Met MHA: Basal + ¹⁴C-MHA-Ca |
| Feeding | Individually fed with Met labelled feed |
| Parameters | 1, 2, 3, 4 or 6 h post-feeding (n = 6-7 fish for each diet and period), |
Trial results
Trial I: Performance response of Nile tilapia to Met sources
- DLM diet significantly improved growth, FCR, and protein efficiency ratio compared to the basal diet. MHA diet showed only numerical improvements in performance, with no significant difference from the basal treatment.
- Calculated on total fish weight gain per tank, the DLM diet produced 214 g more biomass gain whereas the MHA diet produced only 124 g more biomass gain, both compared to the basal diet. Thus, the MHA diet produced 42% less biomass gain than the DLM diet when compared with the basal treatment.
Trial II: Metabolic response of Nile tilapia to labelled Met sources
- The amount of radioactivity (disintegrations per minute; DPM) present in the incubation water and different parts of fish (muscle, liver, viscera, and other parts) was determined (Figure 1).
- In fish fed the DLM diet, the tracer was available to the Residual Free fraction (Free fractions in head, heart, kidney, bones and fins) faster than in MHA fed fish. Moreover, for the 6 h trial, the cumulative Met source bioavailability in Residual compartment was higher in DLM than in MHA fed fish.
- At the end of the incubation period (six hours) a significantly higher amount of tracer was determined in the viscera and muscle protein fractions from DLM fed fish as well as in their livers and residual tissues (Figure 1 and 2; p < 0.05). This indicates a higher bioavailability of DLM compared with MHA when fed on equimolar basis.
- MHA fed fish showed 2.4 times higher area under the curve relative to DLM fed fish for the incubation water. Higher amount of radioactivity present in the incubation water for the MHA fed fish indicates more MHA was evacuated (non-absorbed) and/or catabolized., elucidating why MHA was less deposited in the muscle compared with DLM (Figure 3).
- In sum, more DLM was available in the muscle and different body parts for protein synthesis, and less DLM was catabolized or excreted compared with MHA.
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