Crude glycerol in diets for Nile tilapia sex reversal (Oreochromis niloticus, Linnaeus 1758)
Fabio Meurer1,3, Aldo Tovo Neto2, Lilian Carolina Rosa da Silva3, Luana Cagol3, Marise Taise
Theisen3 & Lilian Dena dos Santos3 1Programa de Pos-Graduac~ao em Zoologia, Universidade Federal do Parana, Palotina, Brazil 2Bolsista DTI-C do CNPq, Laboratorio de Nutric~ao de Organismos Aquaticos, Universidade Federal do Parana, Palotina,
Brazil 3Programa de Pos-Graduac~ao em Aquicultura e Desenvolvimento Sustentavel, Universidade Federal do Parana,
Correspondence: A Tovo Neto, Universidade Federal do Parana, Setor Palotina, Rua Pioneiro 2153, Jardim Dallas, Palotina,
Parana 85950-000, Brazil. Email: firstname.lastname@example.org
Tilapia is a relatively fast-growing fish with low feed requirements, and thus sometimes referred to as the ‘aquatic chicken’ (Josupeit 2005). Nile tilapia is an important fish for Brazil and the increased availability of glycerol, derived from biodiesel production, led to interest in the study of its inclusion in this species’ diet. Glycerol is the main byproduct of biodiesel production (Li, Minchew, Oberle & Robinson 2010) and has a number of applications in the industry (Arruda, Rodrigues & Felipe 2007) after high cost purification procedures. Opportunities may exist to use glycerol as an energy source for livestock (Donkin, Koser, White, Doane & Cecava 2009).
One of the potential uses for crude glycerol is in fish feeding. Li et al. (2010) evaluated its inclusion in diets for channel catfish (Ictalurus punctatus) and Meurer, Franzen, Piovesan, Rossato and dos
Santos (2012) concluded that crude glycerol has a good energy value for Nile tilapia. However, there is little information about glycerol inclusion in diets for this species (Da Costa 2012; Neu, Furuya,
Yamashiro, Bittencourt, Moro, Fernandes, Boscolo & Feiden 2012; Neu, Furuya, Boscolo, Potrich, Lui & Feiden 2013). The purpose of this experiment was to evaluate the inclusion of crude glycerol, derived from biodiesel production, as a substitute carbohydrate/energy source for Nile tilapia diets, during the sex reversal phase.
The experiment was conducted at the Aquatic
Organisms Nutrition Laboratory from Federal University of Parana, Palotina Sector. Nine hundred
Nile tilapia postlarvae (14 1 mg), from GIFT strain (Aquacultura Tupi, Guaıra, Parana, Brazil) were used and distributed in a completely randomized design with six treatments and five replications. For that, 30 plastic tanks (60 L) in water recirculation system connected to a biofilter and eletric thermostat were used as a heating system.
The physicochemical parameters of water from tanks and biofilter, such as dissolved oxygen (5.68 0.91 mg L1) and pH (7.55 0.19), were monitored weekly in the morning to maintain an optimal water quality for the fish in the recirculating system, whereas the temperature was monitored daily, morning (27.47 0.94°C) and afternoon (27.87 0.82°C).
Six experimental diets were formulated (Tables 1 and 2) and treatments were: diet without glycerol (control) and five inclusion levels of crude glycerol (2.2%, 4.4%, 6.6%, 8.8% and 11.0%), aiming to replace all the corn diet, and supply the entire energy value. The feed was provided ad libitum, five times a day. Daily, before last afternoon feeding, tanks were syphoned for removal of faeces and possible feed remains.
At the end of the trial (27 days) fishe were slaughtered by immersion in ice water (1°C), and individually weighed and measured (Standard © 2015 John Wiley & Sons Ltd 1
Aquaculture Research, 2015, 1–4 doi:10.1111/are.12714
Length) to calculate the performance parameters.
Performance parameters evaluated were growth, feed conversion, survival and carcass yield. Posteriorly, carcass yield of fingerlings were evaluated (with and without head). The samples were identified and stored at 20°C for subsequent analyses.
All carcass, viscera and head samples were unfrozen at 0°C, grounded, homogenized and analysed in triplicate for chemical composition determination (dry matter, ash, crude protein and ether extract).
Data were submitted to Variance Analysis (ANOVA) at 5% level of probability through Statistica 7.0 software (Statsoft, Tulsa, OK, USA). All parameters were not influenced (P > 0.05) by glycerol inclusion levels in the Nile tilapia feed (Table 3).
Glycerol has not affected tilapia growth during the sex reversal period. Our findings agree with
Neu et al. (2013) and Neu, Furuya, Yamashiro, et al. (2012), who found that glycerol did not affect the final weight of Nile tilapia juveniles and fingerlings respectively. Feed conversion did not vary with glycerol inclusion levels in diet, similar found by Neu, Furuya, Yamashiro, et al. (2012) and Neu et al. (2013) using the same species, and
Li et al. (2010) for channel catfish. This demonstrated that glycerol, replacing corn, did not affect consumption and weight gain.
Crude glycerol may contain methanol, which is toxic at higher levels to animals (Li et al. 2010).
In the feed pelletizing process, they were dried in conventional kiln, eliminating by this way the entire residual methanol. Survival also was not affected by levels of glycerol in diets, demonstrating that glycerol had no influence on this parameIngredients (*)
Glycerol inclusion levels (%) 0.0 2.2 4.4 6.6 8.8 11.0
Soybean meal 50.15 50.59 51.04 49.96 50.41 51.96
Fish meal 28.00 28.00 28.00 29.00 29.00 28.27
Corn 12.85 10.24 7.63 5.72 3.11 0.00
Glycerol 0.0 2.2 4.4 6.6 8.8 11.0
Soybean oil 6.50 6.47 6.43 6.22 6.18 6.27
Mineral and vitamin† 2.00 2.00 2.00 2.00 2.00 2.00
Salt 0.50 0.50 0.50 0.50 0.50 0.50
Total 100.00 100.00 100.00 100.00 100.00 100.00 *Every diet contained 60 mg kg1 of 17-a-methyltestosterone. †Warranty level by kilogram of product: folic acid: 200 mg; pantothenic acid: 4000 mg; Biotin: 40 mg; Copper: 2000 mg; Iron: 12 500 mg; Iodine: 200 mg; Manganese: 7500 mg; Niacin: 5000 mg; Selenium: 70 mg; A vitamin: 1 000 000 IU; B1 vitamin: 1900 mg; B12 vitamin: 3500 mg; B2 vitamin: 2000 mg; B6 vitamin: 2400 mg; Acid ascorbic: 50 000 mg; D3 vitamin: 500 000 IU; E vitamin: 20 000 IU;