# Management of the First Feeding of Dorada _Brycon sinensis_ with Two Species of Cladocerans
## 2 Materials and Methods  
The study was conducted at the Fisheries Research Institute of the University of Cordoba (CINPIC), located in Monteria (Colombia). Cladocerans _Moina minuta_ (length 690.2 \(\pm\) 10.2 \(\upmu\)m and width 416.1 \(\pm\) 11.7 \(\upmu\)m) and _Macrothrix elegans_ (length 492.9 \(\pm\) 3.0 \(\upmu\)m and width 293.7 \(\pm\) 2.7 \(\upmu\)m) were isolated following the methodology of [PERSON], et al. [29] from zooplankton samples collected in the CINPIC ponds with a conical net of 250 \(\upmu\)m of mesh. Identification of the cladocerans was carried out using the taxonomic keys described by [PERSON] [30]. The initial strains and inoculum, which were maintained in the Living Food Laboratory of the CINPIC, were placed in 200-mL glass bottles, in water filtered through a 20-\(\upmu\)m mesh, kept in a photoperiod 10:14 h (light:darkness) and 30% of the water volume was renewed every 48 h to remove organic matter from the bottom. Daily feeding was based on a mixture of the microalgae _Ankistrodesmus_ sp. and _Scenedesmus_ sp., at a concentration of 4 \(\times\) 10\({}^{5}\) cell mL\({}^{-1}\), determined by cell counting in a Neubauer chamber. The increase in the biomass of the cladocerans was obtained using successive inoculations and the serial volume method [29]. The larvae of dorada and _Piractus brachyponus_ were obtained by reproduction induced with carp pituitary extract (5 mg/kg of live weight), applied in two doses of 20% and 80% at an interval of 12 h [2]. Incubation of the fertilized eggs was performed in 60-L cylindrical-conical upflow incubators; after hatching (70%), the dorada larvae were transferred to circular fiberglass tanks with a useful volume of 1000 L. At the beginning of exogenous feeding (22 hae), 4000 dorada larvae of were distributed in 16 aquaria of 5 L of useful volume, at a density of 50 larvae L\({}^{-1}\). In addition, a sample of 100 larvae was fixed in 1% buffered formalin to measure the initial weight (1.2 \(\pm\) 0.15 mg) and total length (5.9 \(\pm\) 0.4 mm). The larvae were feed treatments, with four replicates each, _M. minuta_ (Mm), _M. elegans_ (Me), and a mixture of these cladocerans (50:50) (Mix). The cladocerans were offered at the rate of 20 prey mL\({}^{-1}\), once for 24 h, and another group was fed freshly hatched larvae of _Piractus brachyponus_ (FL) (4.5 \(\pm\) 0.9 mm) in a 2:1 ratio (prey:predator) [2]. This group was considered the control treatment. The proximal composition of the different prey offered to the dorada larvae was analyzed according to the AOAC official methods [31]. After 24 h, the survival, natural mortality, cannibalism mortality, stress resistance test, growth, and gut contents were evaluated. The survival (S) was assessed using the formula S = (N\({}_{\mathrm{F}}\)/N\({}_{\mathrm{O}}\)) \(\times\) 100, where N\({}_{\mathrm{F}}\) was the final number of live larvae, and N\({}_{\mathrm{O}}\) was the initial number of larvae. Larval quality was evaluated by stress resistance test (S\({}_{\mathrm{R}}\)), which was considered an indicator of the management; from each experimental unit, the larvae were removed (n = 10) with a mesh of 400 \(\upmu\)m and maintained for six minutes in conditions of severe hypoxia; then they were returned to the experimental units, and after 15 min the larvae that survived the test were counted. The S\({}_{\mathrm{R}}\) was assessed using the formula S\({}_{\mathrm{R}}\) = N\({}_{\mathrm{AL}}\)/N\({}_{\mathrm{T}}\)\(\times\) 100, where N\({}_{\mathrm{AL}}\) was the number of alive larvae, and N\({}_{\mathrm{T}}\) was the total number of larvae treated to the severe hypoxia conditions [2]. The mortality for cannibalistic behavior (C\({}_{\mathrm{M}}\)) was assessed by counting the dead larvae that showed mutilation or bite under a inverted microscope ([PERSON], Stemi 2000-C, Jena-Germany). It was estimated using the formula C\({}_{\mathrm{M}}\) = (cannibalized larvae/total initial larvae) \(\times\) 100.