# Management of the First Feeding of Dorada _Brycon sinensis_ with Two Species of Cladocerans
## 4 Discussion
The results of stress resistance in the present study suggest that the larvae of _B. sinuensis_, fed the different live prey evaluated, were in good condition for handling and transfer to the next phase of rearing culture. Mortality due to cannibalism was registered in all treatments but was higher when _M. elegans_ (39.6 \(\pm\) 6.7%) was offered. This result suggests that cannibalism in this treatment was related to the cladoceran distribution (_M. elegans_) in the experimental units, which reduced the feeding availability for dorada larvae in this treatment. [PERSON], et al. [2] established that cannibalism in _B. sinuensis_ is a feeding strategy associated with food availability. When the availability of prey decreases, the search for food increases; this implies an increase in energy expenditure [40]. Therefore, when fed _Macrothrix elegans_, the dorada larvae increased their cannibalism. The adequate prey densities for the larvae is critical for increasing their intake. Different densities of zooplankton have been successfully used in other studies to reduce cannibalism and obtain satisfactory survival rates in the larval stage. In larvae with cannibalism similar to _B. sinuensis_, the following prey densities were found: 0.2 prey mL\({}^{-1}\) (_Artemia franciscana_) [36], 0.5 pre mL\({}^{-1}\) (_Miona_ sp., _Diphunosoma_ sp., _Artemia salina_, _Diaptomus_) [9; 41], 10 prey mL\({}^{-1}\) (_Diaptomus_ sp., _Diphunosoma_ sp., _Moina_ sp. and _Moinodaphmia_ sp.) [37], and 0.1 prey mL\({}^{-1}\) (_Brachionus placitulis_, _Ceriodaphnia reticulata_, _Apcyclops dengizicus_) [42]. The density of cladocerans used in this study (20 prey mL\({}^{-1}\)) was higher than those reported in previous studies, suggesting that a homogeneous distribution of prey must accompany a high density to reduce cannibalism because it reduces the period of searching for prey and increases predator-prey encounters. The natural mortality recorded in the present study was low and similar to the report of [PERSON], et al. [2], who found natural mortality of less than 10% in the management of first feeding of dorada when fed forage larvae (_Prochilodus magdalene_). Thus, the results of the present study suggest that cannibalism is the main cause of mortality in the management of the first feeding of dorada. In all treatments, mortality due to cannibalism was higher than natural mortality, but in larviculture worked with _M. minuta_ this behavior was reduced to its minimum rate (20%), which was less than half of the mortality observed with the other offered prey. The highest LG, WG, and G values were recorded when the dorada larvae were fed with forage larvae (_P. brachypomus_). This result is possible because larger prey allows greater energy efficiency for larvae than small prey. According to the optimal foraging theory, predators select prey that provide a high energy gain per unit of effort [40]. These authors claim that cannibalistic juveniles of _Lates calcarifer_ choose smaller conspecific when given a range of different sizes as prey. This behavior characterizes those cannibalistic predators that obtain high energy gain with the prey of similar or smaller size. Likewise,Atencio-Garcia, et al. [3] found higher values of L\({}_{\rm G}\) and W\({}_{\rm G}\) for _B. amazonicus_ when fed forage larvae (_P. brachypomus_) compared to zooplankton, and they attributed this increase of growth to the lower energy expenditure in the capture of the forage larvae. The appropriate size of the prey allows the predator to save more energy in catching and ingestion than a larger number of smaller organisms. Some authors consider that the density of prey defines growth and that the size of the food may be even more critical. A widely recorded pattern is the increase in growth rate and efficiency caused by increased prey size [43].