A double layers pond aquaculture cage for family breeding of Luciobarbus capito fry and fingerling

Cage aquaculture was originated in China at first and then was spread throughout the world gradually. In the late 1970s, there was a new development in the methods and species of cage aquaculture in freshwater cages in China. Floating cage is the most widely used aquaculture method. Floating cage require a minimum size of stocking fry, and fry must be cultivated to a suitable size before they can be cultured in the cage. In addition, with the growth of the fish, it is necessary to replace the cage with a larger mesh in time. After the cage is in the water for a period of time, it can easily be blocked by the adhesion of algae. In order to solve the problem that fry in the existing cage culture needs early cultivation and high frequency of cleaning and replacement of floating cage and fixed cage when experimental fish are cultivated, a double layers submerged cage was developed for the breeding aquaculture of fry and fingerling in pond. The cage net is composed of an upper large mesh size (0.6 cm) and a lower small mesh size (0.42 mm). The fry was cultivated in the lower small mesh net, whereas the fingerling was cultivated in the enclosed space of the upper large mesh net and the lower small mesh net with a gradual increase of water. Through the comparison between double layers cage and floating cage in pond aquaculture, the results showed that the fry and fingerling could be continuously cultured in double layers cage, while the large-scale fry (full length >2.0 cm) and fingerling could be cultured in floating cage. The total length, body length, body weight, weight gain and specific growth rate of fingerlings fish cultured in double layers cages were significantly higher than those in floating cages (P<0.05). During the three months breeding period, the double layers cage did not need to be replaced and cleaned, and the floating cage was to be replaced five times and cleaned six times. The results showed that the culture effect of the first-year-old fish in the double layers cage was significantly better than that in the floating cage, and the intensity of culture management was significantly reduced. To verify the breeding effect of this system, six double layers cages with the same specifications were installed in a 660 m² pond in parallel. The saline-alkali tolerant breeding families of Luciobarbus capito were selected as breeding objects, culturing from fry to fingerling was completed without replacing or cleaning the cage. The body length was 13.87-16.07 cm and the weight was 34.71-42.07 g, which was a similar size to the one-year-old L. capito obtained under pond aquaculture condition. Moreover, six families showed different growth characteristics (P<0.05). The research showed that the same breeding conditions and accurate growth data can be provided for the fish family selection by double layers cage aquaculture in pond. The double layers cage can provide a pond aquaculture method for fish selective breeding.