Table 5 Ž
. Biochemical composition dry matter of spotted sand bass juveniles fed different dietary protein levels
Ž .
MeanSD Ž .
Protein level 40
45 50
Whole fish Ž .
Crude protein 57.860.52
57.241.33 56.620.62
Ž . Ether extract
28.161.07 28.800.24
29.420.68 Ž .
Ash 13.430.14
13.210.30 12.520.30
Ž .
Gross energy calrg 566669
568667 572777
Ž . Moisture
74.100.04 72.350.08
71.380.06 LiÕer
Ž . Crude protein
15.240.03 14.240.44
13.730.55 Ž .
Ether extract 64.240.47
66.371.28 69.710.27
Ž . Ash
1.670.15 1.480.02
1.470.07 Muscle
Ž . Crude protein
70.911.15 72.160.32
72.710.58 Ž .
Ether extract 22.642.26
22.470.82 20.970.58
Ž . Ash
5.600.23 5.680.23
5.870.22
69.7 for diets containing 40 and 50 dietary protein, Nevertheless, no differences in whole fish, liver, or muscle composition were found among dietary treatments.
4. Discussion
In this study, the 45 dietary protein level showed significantly better growth performance than the 40 protein level. This protein level is similar to those reported as
required by other carnivorous fish, whereas it is higher than that recommended for Ž
omnivorous or herbivorous fish such as tilapia, catfish, and carp Davis and Stickney, .
1978; Ogino, 1980; Robinson and Robinette, 1994 . The difference in results from one Ž
study to another can be explained by the different experimental conditions feeding .
methods, species, age, sex, and stocking density used. In some cases, when the protein requirement is exceeded, the growth rate remains constant or decreases because dietary
Ž .
protein is used to metabolize the excess amino acids absorbed Jauncey, 1982 .
Ž Accumulation of lipid in tissue and muscle has also been reported Ballestrazzi et al.,
. 1994; Swann et al., 1994 . The growth rate of spotted sand bass obtained in the present
study can be considered satisfactory, because lower values have been found for other Ž
. species, such as Mediterranean yellowtail Seriola dumerilii Jover et al., 1999 . In
contrast, higher values have been reported for grouper Epinephelus tauÕina, barramundi Ž
. Ž
. Tacon et al., 1995 , or rabbitfish Parazo, 1990 . In a previous growth trial with spotted
sand bass juveniles cultured in floating cages where the fish were fed a diet made with Ž
. fresh tuna and squid as the main protein sources 56 protein and 22 ether extract ,
Ž .
Grayeb-Del Alamo et al. 1998 found ADG values varying from 0.27 to 0.32 grday.
The lack of control of environmental conditions in the cages and diet composition may have affected the growth performance; nevertheless, the higher ADG values found by us
Ž .
Ž .
0.36 to 0.40 grday with diets containing lower protein 40–50 protein represent an improvement for the rearing technology of the spotted sand bass.
Ž .
Ž .
The protein efficiency ration PER values 1.48, 1.42 and 1.34 for dietary protein levels 40, 45 and 50 are higher than those obtained in a previous experiment
Ž .
where spotted sand bass juveniles 2.5 g were fed semipurified diets containing casein Ž
. Ž .
as main protein source 1.12, 1.21 and 1.15 Anguas-Velez, personal communication .
´
The difference in these results could be related to a more balanced amino acid composition in the practical diets compared to the semipurified diets, since it is known
Ž .
that casein is limited in arginine for many species studied Chen and Tsay, 1994 . Similar PER values have been reported for other species like gilthead seabream
Ž .
Ž 1.5–1.2, 42–50 dietary protein, Robaina et al., 1997 ; European sea bass 1.66–1.18;
. 45–50 dietary protein, Ballestrazzi et al., 1994 , indicating that protein from the
practical diets was used efficiently by spotted sand bass independently of the dietary protein level.
Significantly higher GER was detected in fish fed diets containing 45–50 protein, compared to fish fed the 40 protein diet. These values are higher than those of gross
Ž .
energy efficiency reported by Jover et al. 1999 for Mediterranean yellowtail juveniles Ž
. 12.5–15.2 for diets containing 45–50 protein , and similar to those reported by
Ž .
Ballestrazzi et al. 1994 for European sea bass fed diets containing 44–49 crude protein. DPG was also found to be higher in spotted sand bass fed diets containing 45
and 50 protein compared to fish fed the 40 protein diet, which is in accordance to the growth rates observed. In contrast, no effect of the dietary treatments was detected
Ž .
on the daily feed intake, protein productive value PPV , or the daily energy gain. In Ž
. Ž
rabbitfish Siganus canaliculatus Yousif et al., 1996 and Siganus guttatus Parazo, .
1990 , PPV values were found to be 29.3 with 35 dietary protein level, and 30.7 Ž
. with 36 dietary protein level. Robaina et al. 1997 in gilthead seabream, found values
from 21.9 to 25.2 feeding a diet with a 55 protein. PPV values found here with spotted sand bass indicate that protein assimilation was relatively high with all dietary
treatments. Since protein is the most expensive component in finfish feeds, it is necessary to minimize the protein content of the diet, but to provide the essential amino
acids required by the organisms to support good growth. Special attention has to be
Ž .
taken to the feed conversion ratio or the feed efficiency , which are reliable variables for fish farmers. In our work, when the protein level in the diet increased, the feed
conversion ratio decreased, but no significant difference was observed among treat- Ž
. ments. The FCR values obtained here for the spotted sand bass 1.43–1.60 are similar
or lower than those reported by several authors for commercially cultured species, such Ž
. Ž
as estuary grouper 1.67–2.85; Teng et al., 1978 and red drum 2.14; Serrano et al., .
Ž .
1992 . Grayeb-Del Alamo et al. 1998 found a FCR of 2.3 for spotted sand bass juveniles reared in cages, whereas a previous study in our laboratory on smaller
juveniles of the same species resulted in feed conversion ratios varying from 4.5 to 1.5 when casein was used as sole protein source. These results indicate the diets used here
were better suited to meet protein requirements of the juveniles. The experimental diets evaluated by us do not give an accurate estimation of the protein requirements because
the digestibility of the ingredients is not known. However, no significant effect of dietary protein level was observed on chemical composition of whole fish, muscle, or
liver. A plausible explanation for lack of significant differences in the body or tissue composition may be the short time of the growth trial, considering the size of the
Ž .
organisms employed, as has been found in other studies Lazo et al., 1998 .
5. Conclusion
