Selective Behavior of Juvenile Brachymystax tsinlingensis Depends on Substrate Color, Light Intensity, and Light Color

Abstract

Brachymystax tsinlingensis is a unique cold water fish locally distributed in China, belonging to Salmoniformes, Salmonidae and Brachymystax. It is mainly distributed in the mountain streams of the Qinling mountain range, including the Shitouhe River in the northern foothills, the Heihe River in the eastern foothills and the Taibaihe and Xushuihe rivers in the southern foothills. B. tsinlingensis has high sensitivity owing to demanding natural habitat conditions and special biological properties. In the past few decades, environmental pollution, a variety of human-caused threats, and reduced resources has caused drastic declines in the wild populations of B. tsinlingensis. In 1998, the species was listed as a second-class state-protected wild animal in the China Red Data Book of Endangered Animals. Due to environmental disruption and human impacts, wild numbers of this species have declined quickly. In China, researchers have focused on B. tsinlingensis conservation. Artificial propagation is one of the most effective methods to restore the natural populations of B. tsinlingensis. In recent years, initial breakthroughs in artificial propagation techniques have aided this species, but the fry survival rate remains relatively low. During artificial breeding experiments, we identified the light environment and substrate conditions that are important factors affecting the survival rate of fry. Fry behavioral selection of light and substrate characteristics was highly significant. The aim of this study was to identify the habitat preferences and associated behavior of B. tsinlingensis. Behavioral experiments were conducted on the progeny of B. tsinlingensis in response to the light environment and substrate color. In this study, we randomly selected healthy juveniles from the same offspring batch obtained through artificial propagation as the experimental fish. The fry total length ranged from 2.23–4.57 cm, with an average of (3.31±0.67) cm. Fry weight ranged from 0.21–0.77 g, with an average weight of (0.42±0.18) g. The experimental fish were not fed 2 h before initiating the experiment. We undertook a combination of individual tests and population tests to investigate three different behavioral selection experiments on juveniles: substrate color preference with the substrate colors of black, white, and blue; light intensity preference with the light intensity of dark (from 1 lx to 5 lx), transition area (from 5 lx to 10 lx), and illuminated area (from 10 lx to 25 lx); light color preference with the light colors of yellow, red, green, or blue. The statistical analysis of the percentage of residence time and the distribution number of experimental fish in each area, enabled analysis using a selective index for the different light intensities, different light colors, and different substrate colors. All analyses used Excel 2016 and SPSS (V 25.0) software, and the statistical values were expressed as the mean ± standard deviation. The results showed that the percentage of time the individuals resided in the black substrate area was significantly higher than that in the white or blue area (P 0.05), and the percentage of the population in the illuminated area was significantly lower than that in the dark area and the transition area (P 0.05). However, the percentage of individuals in the green light area was significantly lower than that in other areas (P < 0.05). The population had a negative tendency towards the green light, and fish displayed sudden acceleration when swimming through the green area in the light color selection experiment. Consequently, the population had a more pronounced avoidance than the individual experiments, this might be related to the mutual transmission of information when residing in clusters, and the speed of information transmission in groups encouraging individuals to avoid the adverse environment. Juvenile B. tsinlingensis preferred a black substrate, avoided green light, and their optimum illumination range was 1–10 lx. The results provide scientific guidance for environmental fry rearing and releasing of B. tsinlingensis.

Keywords

• substrate environment
• light
• behavior selectivity
• brachymystax tsinlingensis
• juvenile