Introduction
In order to optimize the production of Argyrosomus regius (Asso, 1801), various studies related to improving its growth are being carried out. Fish growth is affected by environmental factors such as salinity, photoperiod and temperature (Boeuf and Payan, 2001). The effects of salinity on growth rate may be secondary to the increased energy costs of osmotic and ionic regulation that limits the energy available for growth (Laiz-Carrión et al., 2005). The aim of this paper is to test the influence of two different salinities on growth and feed efficiency of juvenile A. regius.
Materials and Methods
The experiment was carried out at the facilities of Centro IFAPA El Toruño. Juvenile meagre (n=234; 6.94±0.04cm total length and 4.32±0.07g whole-body wet weight) were randomly divided in 8 tanks of 125L and reared during 6 weeks (45 days) under two different environmental salinities (12 and 39). Fish were fed daily with commercial dry pellets at a ration
of 4.4%.bw.day-1. Several parameters of the water were measured daily: temperature (ºC), oxygen (ppm) and salinity (g.L-1) or weekly: pH, nitrite (ppm), ammonia (ppm) and flow (L.min-1). The average temperature was maintained at 22.4±0.1ºC. Every week, 15 fish from each tank were randomly selected, were anaesthetized with clove oil (0.13ml.L-1) and total length
(TL) and body weight (BW) were recorded using a measuring board and a digital balance, respectively. The following parameters were calculated: condition factor (K), daily growth rate (DGR), specific growth rate (SGR), food conversion rate (FCR) and protein efficiency ratio (PER). The data were tested by one-way ANOVA for the elimination of atypical values statistically and Tukey’s test for the comparison of averages between the different groups.
Results and Discussion
Mortality observed, throughout the experimental period, was 2% at salinity 12 and 3% at salinity 39. The environmental parameters did not show statistically significant differences between groups throughout the experiment. The absence of changes among group further supports that changes observed in growth and feed efficiency (Table I) could be attributed to the different salinity. Juvenile A. regius exposed to salinity 39 presented lower growth compared to animals kept at 12. Differences between groups became statistically significant on day 7, in total length, and on day 14, in body weight, and remained so until the end of the experiment (P<0.05). Condition factor (K) was significant differences on 21 day with better values at salinity 12. In addition, juvenile meagre maintained at salinity 12 had a better results in DGR, SGR, FCR and
PER than fish exposed to salinity 39. In all parameters calculated were observed significant differences between groups (P<0.05).These results are similar to the observed in juvenile of sciaenid species such as Argyrosomus japonicus (Fielder and Bardsley, 1999) with better growth at salinities between 5.0 and 12.5; and Argyrosomus inodorus (Ferreira and Kaiser, 2008) where better growth was observed at salinity below 35. In posterior phases of cultivate A. regius also presents better growth in salinity 13 (El-Shebly, et al., 2007; Muñoz et al., 2008). In juveniles of other euryhaline species such as Pagrus pagrus (Vargas-Chacoff et al., 2009) and Sparus aurata (Laiz-Carrión et al., 2005) were observed also better growth rates at salinities below 35. According to the results obtained, we could say that it is possible to culture juvenile meagre at low salinities, with higher growth and better food efficiency.