Abstract
This trial was conducted to determine the dietary digestible methionine + cystine requirement of Nile tilapia (550 to 700 g) based on the ideal protein concept. Six hundred fish were distributed in a completely randomized design with five treatments and four replicates, with 30 fish per experimental unit. The fish were fed diets containing approximately 262 g of digestible protein/kg, 3,040 kcal of digestible energy/kg and 7.90, 9.40, 10.90, 12.40 or 13.90 g of methionine + cystine/kg. The fish were hand-fed three times a day until apparent satiation for 30 days. No effects of dietary methionine + cystine on feed conversion ratio, daily protein deposition, whole body moisture, fillet moisture, crude protein, ether extract and ash, plasmatic HDL and LDL cholesterol were observed. Dietary methionine resulted in a linear increase in whole body protein and linear reduction in lipid deposition rate, hepatosomatic index, whole body ether extract and ash, plasmatic total cholesterol, plasmatic total lipids and plasmatic triglycerides. According to the Linear Response Plateau, the daily weight gain and fillet yield increased up to a level of 9.00 and 9.90 g methionine + cystine/kg of diet, respectively. The digestible methionine + cystine requirement of Nile tilapia is 9.00 g/kg for weight gain and 9.90 g/kg for fillet yield, corresponding to methionine + cystine:lysine ratios of 0.60 and 0.66, respectively.
Highlights
Tilapia is one of the most important freshwater farmraised fish and has had an increasing role in the global aquatic food trade
The dietary methionine supplementation has been indicated mainly in diets based on soybean protein, which have methionine as the first limiting amino acid for carnivorous fish like rainbow trout, Oncorhynchus mykiss (Gaylord et al, 2007); Atlantic salmon, Salmo salar (Hansen et al, 2007); cobia, Canadum rachycentron (Chou et al, 2004); and cod, Gadus morhus (Hansen et al, 2007), and omnivorous fish like carp, Carassius auratus (Hu et al, 2008); Nile tilapia (Santiago & Lovell, 1988; Furuya et al, 2001; Nguyen & Davis, 2009); channel catfish, Ictalurus punctatus (Harding et al, 1977; Cai & Burtle, 1996); and pacu, Piaractus mesopotamicus (Abimorad et al, 2009)
The values of digestible protein and amino acids, digestible energy and available phosphorus were obtained from Furuya et al (2001b), Pezzato et al (2002) and Guimarães et al (2008a, b), in studies conducted with the Nile tilapia
Summary
Tilapia is one of the most important freshwater farmraised fish and has had an increasing role in the global aquatic food trade. No effects of dietary methionine + cystine on feed conversion ratio, daily protein deposition, whole body moisture, fillet moisture, crude protein, ether extract and ash, plasmatic HDL and LDL cholesterol were observed.
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