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Several investigations have been carried out to improve the productivity of tambaqui, an economically important fish species in Brazil and other Latin American countries. This study determined the digestible protein (DP) requirements in juvenile tambaqui by assessing their productive performance and nutritional efficiency. It also evaluated the effects of different dietary DP levels on the morphology and cellularity of skeletal fast muscle fibres. The 1750 tambaqui tested (6.53 ± 0.43 g body weight, 7.58 ± 0.18 cm length) were randomly distributed into 35 tanks. Fish were fed one of the seven isocaloric diets, which contained 140, 170, 200, 230, 260, 290 or 320 g/kg DP. The DP requirement, calculated by segmented (broken line) regression of weight gain data, was 290 g/kg. An increase in diet DP to 290 g/kg significantly improved final weight, weight gain, feed intake, specific growth rate and crude protein gain, and changed fibre diameter in deep muscle. Muscle fibres were randomly distributed into a mosaic pattern, characterized by fibres with different diameters. Treatments with 290 and 320 g/kg DP increased the frequency of large‐diameter fibres (>50 µm), indicating hypertrophic growth of skeletal muscle during the juvenile phase, which occurred in conjunction with hyperplasia.

This study evaluated the apparent digestibility coefficients (ADC) of essential (EAA) and non-essential (NEAA) amino acids of 13 ingredients for tambaqui (Colossoma macropomum) diets. Proteic and energetic ingredients were analyzed separately. The trial with energetic and proteic ingredients were arranged in a randomized block design, with four replicates: energetic ingredients (corn, wheat bran, broken rice, and sorghum) with four treatments, whereas proteic ingredients (corn gluten meal, soybean meal, poultry byproduct meal, salmon meal, fish meal [tilapia processing residue], wheat gluten meal, feather meal, cottonseed meal, and alcohol yeast [spray dried]) with nine treatments. Each block was considered as one round of fecal collection. A total of 420 tambaqui juveniles (mean initial weight: 70±8.58 g) were used. Among energetic ingredients, corn (94.6%) and wheat bran (91.9%) had the highest ADCEAA, followed by broken rice (75.7%), and sorghum (72.8%). On average, ADCEAA and ADCNEAA values of proteic ingredients were 79.5-98.5%, except for alcohol yeast (ADCEAA: 68.4 and ADCNEAA: 76.7%). Tryptophan was the first limiting amino acid in most ingredients tested and had the lowest chemical scores (0.06-0.51), except for wheat bran, corn gluten meal, and soybean meal, in which lysine was the first limiting amino acid. Soybean meal had the highest digestible essential amino acid index (EAAI: 1.02) and the most balanced amino acid profile, whereas wheat gluten meal had the lowest EAAI (0.48). Overall, tambaqui was very efficient to digest proteic and energetic ingredients.

The study evaluated productive and economic performance, physiological parameters and nutritional efficiency in net cage-reared Nile tilapia fed extruded diets containing four carbohydrate (CHO) and lipid (LIP) ratios. The 1280 fish in the trial were sex-reversed male Nile tilapia from the Gift strain (157.54 ± 3.50 g). Fish were randomly distributed into 16 net cages (1.0 m 3 ), with 80 tilapias per cage. The four practical diets were formulated with the same ingredients at different proportions of starch and soybean oil contained similar digestible protein (251.40 g Kg −1 ), digestible energy (17.39 Mj Kg −1 ) and CHO:LIP ratios of: 3.89, 4.87, 6.14 and 7.83 (CHO 35 /LIP 9 , CHO 39 /LIP 8 , CHO 43 /LIP 7 and CHO 47 /LIP 6 , respectively). The diets were provided four times a day, for 120 days. Fish fed a CHO 43 /LIP 7 diet exhibited the best productive performance, with 252.01% percent weight gain (WG), 1.07 ± 0.028% daily specific growth rate (SGR) and 462.08 ± 5.06 g feed intake (FI). Fish fed the CHO 43 /LIP 7 diet also showed the highest gross energy retention efficiency (57.17 ± 4.16%) and LIP use for weight gain (13.71 ± 1.47%). CHO 39 /LIP 8 and CHO 43 /LIP 7 diets produced the best economic performance,

A qualidade da dieta pode ser avaliada quantificando a habilidade dos peixes para digerir os alimentos. Portanto, este estudo teve como objetivo determinar os coeficientes de digestibilidade aparente (CDA) para proteína bruta (PB), extrato etéreo (EE) e energia bruta (EB) de nove ingredientes proteicos e sete ingredientes energéticos mais comumente usados em dietas comerciais para tambaqui. No total, 510 juvenis de tambaqui foram alimentados com dietas-teste contendo uma dieta de referência suplementada com um marcador de digestibilidade inerte (Cr2O3). As análises de digestibilidade mostraram que o glúten de milho apresentou o CDAPB(98,09%) e CDAEB (96,91%) mais alto, enquanto que a levedura de álcool apresentou o menor CDAPB (63,17%) e CDAEB (46,24%). Os ingredientes proteicos foram revelados como excelentes fontes de lipídios (CDAEE > 85,0%), com exceção do glúten de trigo (CDAEE: 63,73%). O milho (94,5%) e o farelo de trigo (86,08%) apresentaram o CDAPB mais alto de todos os ingredientes energéticos. Não foram observadas diferenças significativas no CDAEE dos ingredientes energéticos testados. Dos ingredientes energéticos testados, o óleo de milho (95,7%), óleo de peixe (93,61%), o óleo de soja (93,31%) e o milho (88,70%) apresentaram o CDAEB mais alto. O uso de ingredientes proteicos e energéticos com altos coeficientes de digestibilidade, como os relatados, pode orientar a formulação de dietas de alta qualidade para tambaqui.

This study evaluated the application of stable isotopes of carbon as an alternative and more accurate method to determine gastrointestinal transit time (GTT) in fish by comparing it to the inert marker method. The stable isotope method detects alterations of the normal carbon flow in a biological system by analyzing naturally occurring isotopes of carbon, contrary to studies based on conventional techniques that apply external markers to the diet to determine GTT through visual observation of the color change in feces. Therefore, 320 pacu, Piaractus mesopotamicus juveniles were reared in 32 tanks under two different temperatures (25 and 29 C). The pacu juveniles received two different diets, one based on ingredients derived from C3 photosynthetic cycle plants and the other based on C4 plant ingredients, both containing titanium oxide (TiO2) as a marker. After 40 d, the isotopic signature of the diets was changed, and the marker was replaced by chromic oxide (Cr2O3). In the isotopic technique, the feces were analyzed to determine the exchange in the isotopic ratio of carbon δ13C. Both methods found that GTT was faster (nearly 6 h) in fish at 29 C when using the C4/C3 feeding strategy and slower in fish at 25 C using the C3/C4 strategy (15 h by inert marker and 18 h by the isotopic method). In conclusion, GTT determination in pacu juveniles using the stable isotope technique exhibits the same accuracy obtained with the inert marker method at temperatures suitable (nearly 29 C) for the metabolism of these animals.

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