Production of cachama reciprocal hybrids in earth ponds. Production of cachama reciprocal hybrids in earth ponds

: The growth of cachama hybrids, cachamoto (Colossoma macropomum ♀ x Piaractus brachypomus ♂) and cachamay (P. brachypomus ♀ x C. macropomum ♂) was compared for 154 days to determine which showed the better productivity. The experiment was carried out in three earth ponds, each divided transversely with a plastic net, yielding six experimental units. Juveniles of cachamoto of 12.95±2.43g and 6.75±0.42cm and cachamay of 16.65±3.64g and 7.41±0.62cm were distributed in each sub-tank of 240m 2 at a density of 0.5 fish m -2 . Fish were fed twice daily except on days when their weight and length, and the physical and chemical parameters of the water were measured. The following productive variables were evaluated: growth in weight and length, daily weight gain, daily feed intake, apparent feed conversion, specific growth rate, condition factor, productivity and the cost/benefit relationship. None of the analyzed variables presented statistical difference between treatments. Physical and chemical parameters of the water remained within the recommended values for cachama, and survival was 100%. Based on the results obtained, it can be concluded that cachama reciprocal hybrids present a similar productive behavior, so that it is indifferent which one is chosen to be raised under the conditions evaluated.


INTRODUCTION
The south western region of Venezuela presents edaphic, hydrological and climatic conditions appropriate for the farming of warmwater continental fish. Since 1986, numerous farms have been established for the farming of the cachamas Colossoma macropomum and Piaractus brachypomus, and in recent years, almost 100% of the farms grow the hybrid of these species; however, uncertainty remains as to which of the two groups of reciprocal hybrids shows the better yield. In terms of farming, the management of hybrids is performed in a manner similar to the pure species. Physical and chemical parameters of water, type and frequency of feeding and adaptation to the culture systems, among other conditions, are similar to parental groups (USECHE, 2001;GONZÁLEZ & HEREDIA, 1989).
Similar to other species, the objective of producing hybrids of the two species of cachama present in Venezuela is to obtain individuals that show advantages of parents and that reflect in a higher productive yield. Several studies have analyzed the growth of these hybrids of cachama (BAUTISTA et al., 1999;SILVA-ACUÑA & GUEVARA, 2002;BAUTISTA et al., 2005; ALENCAR-ARARIPE Ramírez-Mora et al. et al., 2011;LÓPEZ y ANZOÁTEGUI, 2012;UZCÁTEGUI-VARELA et al., 2014;GUEVARA et al., 2016). Maternal contribution to these reciprocal hybrids has not been genetically evaluated; but there may be a difference that could manifest in a higher offspring performance. In addition, due to large number of fish farmers and production of cachama hybrids, these fishes have social and economic important in the region. For this reason, the objective of this study was to evaluate the productive behavior of the reciprocal hybrids of cachamas raised in earth ponds.

Experimental design
Three earth ponds of 480m 2 each were divided transversely with plastic mesh of 3.81cm, generating two experimental units per pond, and three replicas per treatment. In each of them, both groups were placed in completely randomized blocks and no water exchange was made, except replacement by evaporation. The trial lasted 154 days between March and August 2015. Fish were fed twice a day (8:00 a.m. and 4:00 p.m.), except on the sampling days, using commercial extruded feed of 28% crude protein (CP) for the first 60 days and then 24% CP up to the end of the trial. The amount of food supplied was adjusted according to the biomass calculated in the samplings. The water quality parameters were measured every 28 days in each pond: temperature, transparency, dissolved oxygen, pH, alkalinity and hardness using a Pionner multiparameter probe (Pioneer 65 multi meter, France), Secchi disk and a colorimetric water kit (Fresh Water Aquaculture Outfit, Lamotte, USA).

Evaluation of productive and economic parameters
Samples were taken every 14 days of 15% (n = 18 fish) of each replicate (n= 3 replicates), registering weight and length with a digital scale (Ohaus Scout Pro) and an ichthyometer, respectively. However, at the end of the experiment the total number of remaining fishes was counted to calculate

Statistical analysis
A mixed effects model for repeated measures was adjusted. A different unstructured covariance was assumed for each individual, assuming that the intercept is different for each one (random intercept). Data were reported as mean ± standard deviation. In order to analyze the effects of the treatments, one analysis of variance (ANOVA) of a GLM-type was performed, verifying previously the assumption of variance homogeneity (Barlett's test). The significance criterion was P<0.05. Statistical analyses were performed using the SAS 8.2 program (SAS Institute Inc.).

RESULTS
Values obtained for the water physical and chemical variables (Table 1) correspond to both treatments because in each pond there was a replicate of each group. The length/weight ratio was directly proportional for both treatments, which presented the same value of the determination coefficient (r 2 = 0.996). Similarly, the growth coefficient (b) had a value close to three (3) (Figure 1). An increase of weight and length was observed in both treatments, but there were no statistical differences (P≥0.05). There were also no statistical differences (P≥0.05) in productive and economic parameters evaluated (Tables 2 and 3).

DISCUSSION
In the commercial production of fish, one pursues optimization of the productive yield; for this reason, in the present study hybrids have been managed keeping water quality conditions similar to the natural environment. Values of the physical and chemical parameters measured in the ponds of the present experiment were within the desired ranges (GONZÁLEZ & HEREDIA, 1998); however, temperature, transparency, alkalinity and hardness sometimes presented values slightly outside the suggested range, apparently without affecting performance at such times.
The FCR observed in the present study was similar to those verified in C. macropomum (1.72 and 1.78) (PASQUIER et al., 2011;LÓPEZ and ANZOÁTEGUI, 2013) Value of Kn indicated the degree of wellbeing of an individual or population in a given environment and is related to the growth rate and comfort level of the animals (LE CREN, 1951), where: Kn ≥ 1 = good and Kn ≤ 1 = bad (LE CREN, 1951). An isometric growth of the population associated with values close to '1' for Kn would indicate good growing conditions in an evaluated population (HABIT, 2005). The Kn values obtained in the present study were close to '1', which indicated that both groups presented good physiological condition. Values of survival achieved (100%) reinforce this    -VARELA et al., 2014). Productivity achieved in the present study was similar to those obtained in traditional systems (LÓPEZ & ANZOÁTEGUI, 2012;UZCÁTEGUI-VARELA et al., 2014). Another experiment raising cachamoto in earth tanks obtained productivities of 0.61 and 0.50kg m -2 , but lower Wg, DWg and SGR values (SILVA-ACUÑA & GUEVARA, 2002). These higher values compared to the present study are probably due to the fact that they used fish with greater initial weight (123 ± 0.9g). In a non-traditional system of farming (high density tanks), PASQUIER et al. (2011) reported higher productivity (2.14kg m -2 ) in C. macropomum, but with lower values of Wg, DWg and SGR.

CONCLUSION
Results of the present study demonstrated that both hybrids have similar growth and productivity yield. Consequently, we do not suggest a preference for the raising of either of them.  720 720 Stocking density (fish m -2 ) 0.5 0.5 Initial mean weight (