Introduction
Meagre is a widely diffused species that thrives in the Mediterranean but also in the Atlantic Ocean, from north Europe to equatorial Africa. The optimal texture and taste as well as its fast growth and environmental adaptability makes it an ideal candidate for aquaculture exploitation. The production of meagre, which occurs mainly in the southern part of the Mediterranean Sea, outlines how better growth performances can be achieved in warmer temperatures and in areas with milder winters. The scope of this research was to determine the growth potential, feed response and the body characteristics of meagre reared in warmer seawater, such as the Red Sea environment.
Materials and Methods
Two different trials involving juveniles of 115 g (Run 1) and pre-adults of 568 g (Run 2) were carried out in order to assess the growth potential of Argyrosomus regius at different growth stages. The fish in both trials were stocked in 1.1 m3 tanks, with 41 juveniles stocked in triplicates per tank (4 kg m-3) while pre-adult were stocked in number of 16 individuals (8 kg m-3). Fish were fed twice a day for a period of 74 days. Four locally available commercial diets were used, with values of crude proteins and crude fat (CP/CF) for juveniles as follows: 47/14 (Diet 1), 46/13 (Diet 2), 47/12 (Diet 3) and 42/20 (Diet 4). For pre-adults the CP/CF values were similar to the juvenile trial, with the only exception of Diet 2, whose CP/CF was 48/14.
The water salinity in both trials was 41-42 g L-1, while temperature was 25.32 ± 1.21 °C in Run 1, and 27.34 ± 0.7 °C in Run 2.
Fish data was analyzed using one-way ANOVA followed by Fisher Least Significant Difference (LSD) test to compare significant differences between treatments.
Results
The juvenile fish grew between 130 to 209 g during the 74 days of feeding. Final body weight was statistically higher in Diet 1 (324g) than in the other ones (range 295-246 g). Specific growth rate (SGR) resulted highest in Diet 1 with 1.4 (P <0.05), medium in Diet 4 (1.25) and lowest in Diets 2 and 3 (1.00 and 1.04 respectively). The FCR was higher in Diets 1 and 4 (1.09 and 1.18) than Diet 2 and 3 (1.52 and 1.41).
The final body weights of pre-adult fish resulted highest in Diets 1 and 2 (770 g and 733g). Similarly SGR for the same diets were respectively 0.40 and 0.37, higher than Diets 3 and 4 (0.17 and 0.14). The FCR was not statistically different in Diets 1 and 2 (1.61 and 1.85).
The protein efficiency ratio in juveniles was statistically higher in Diet 1 and 4 (1.82 and 2.17 respectively), and in Diets 1 and 2 for pre-adult (1.33 and 1.08).
Proximate composition of the body of pre-adult fish showed no differences in crude protein % but showed higher level of crude fat % in Diets 2 and 4.
Discussion
The current study showed that the growth performances of meagre were comparable to other researches carried out at lower temperatures or salinities. In Run 1 the performances were comparable to the FCR of 1.2 obtained by Martínez-Llorens et al., (2011) using 47% CP and 20% CF. In juveniles the SGRs were similar or higher than the values found in the literature.
In pre-adults the FCR showed similar or even better results than most of the papers with same body weights. However SGRs were slightly lower than the 0.57 obtained by Gültepe et al. (2016) or the 1.77 obtained by Velazco Vargas (2014). The proximate concentration of the carcass of the fishes showed higher percentages of proteins compared to the 15.8-16.7 % of Carvalho et al. (2018).
Conclusions
Meagre tested in the Red Sea conditions proved comparable growth with all the scientific researches carried out in the Mediterranean Sea, particularly for juvenile fish. Some suboptimal performances in pre-adult fish could be motivated by the higher temperatures, the small size of the pellets as well as some nutritional flaws determined by the use of commercial feeds not specifically formulated for meagre.
References
Carvalho, M., Peres, H., Saleh, R., Fontanillas, R., Rosenlund, G.,Oliva-Teles, A., Izquierdo, M., 2018. Dietary requirement for n-3 long-chain polyunsaturated fatty acids for fast growth of meagre (Argyrosomus regius, Asso 1801) fingerlings. Aquaculture 488, 105–113
Gültepe, N., Galip Dorlay, H., İrsad Gültepe, M., Sabri Kesbiç, O., Acar, Ü., Yalgin, F., 2016. Comparation of Diets Used for Larviculture of Meagre (Argyrosomus regius Asso 1801). American Journal of Experimental Agriculture 11, 1-7
Martínez-Llorens, S., Espert, J., Moya, J., Cerdá, M.J., Tomás-Vidal, A., 2011. Growth and nutrient efficiency of meagre (Argyrosomus regius, Asso 1801) fed extruded diets with different protein and lipid levels. International Journal of Fisheries and Aquaculture 3, pp. 195-203
Velazco Vargas, L.G.L., 2014. Contribución al estudio de las necesidades nutritivas de la corvina (Argyrosomus regius, Asso 1801). PhD dissertation, Universitat Politècnica de València.