Otolith fluorescent and thermal marking of elongate loach (Leptobotia elongata) at early life stages

Abstract

The elongate loach (Leptobotia elongata) is an important fish species for artificial release program during the development of hydropower stations in upper Yangtze River drainage. We explored the chemical and thermal marking of otoliths for the species in this study, hoping to provide appropriate marking approaches for it. Chemical marking was conducted by immersing elongate loach in alizarin complexone (ALC) of concentrations 50–250 mg L−1 or alizarin red S (ARS) of concentrations 30–150 mg L−1. The results demonstrated that all concentrations of ALC and ARS treatments had 100 % fluorescent marks in sagittae and lapilli (grade ≥ 3), and that mark quality and mortality increased with increasing of fluorochrome concentration, while decreased with increasing of total length. The optimal conditions of otolith fluorescent marking for larval and juvenile elongate loach were to immerse in 50–100 mg L−1 ALC or 30–90 mg L−1 ARS solutions for 12–24 h. Larvae thermally marked by being exposed to five water temperature regimes represented different patterns of otolith increment. The control of duration in the heated water could produce some narrow or wide increments, and there was a significantly positive relationship between increment width and duration in heated water in each cycle of water temperature fluctuation. More and complicated otolith mark patterns could be produced by combining thermal marking with fluorescent immersion. Considering efficiency, operability and low-cost, the ARS immersing and thermal marking methods are recommended for mass-marking elongate loach at early life stages.