THE PHOTOPERIOD’S EFFECT ON LARVAE OF THE CAUCASIAN TOAD, BUFO VERRUCOSISSIMUS IN LABORATORY CONDITIONS

Abstract

The effect of the photoperiod on amphibian larvae remains poorly understood. Based on the results of previous studies, it can be noted that the effect of daylight hours differs significantly in amphibians in different taxonomic groups. The Caucasian toad, Bufo verrucosissimus, is common in the forest belt of the Caucasus and the Levant. The species is included in the Red Data Books of the Russian Federation, Azerbaijan and South Ossetia. The technology of zooculture of this species is currently being developed. The optimal conditions for growing the larvae of the Caucasian toad, including density and temperature, have been determined. The present study is devoted to the study of the effect of different daylight hours on the duration of development and survival of B. verrucosissimus larvae, the size of young toads after metamorphosis, and the cost of feed for their rearing. The purpose of this work is to identify the optimal light regime for growing the larvae of the Caucasian toad in zooculture. Materials and methods. The material for the research was the offspring from the laboratory breeding of a pair of Caucasian toads caught in the Karachay-Cherkess Republic. The larvae were kept in containers 39 × 28 × 14 cm filled with 9 L of water. The containers (400 lux) were illuminated with fluorescent lamps located at a distance of 5 cm from the water surface. When keeping the larvae, five variants of the photoperiod were used: round-the-clock lighting, 18 hours a day, 12 hours a day, 6 hours a day, round-the-clock lack of lighting. Raising animals under each illumination mode was carried out in triplicate. Results. The length of daylight hours influenced the duration of the larval development of the Caucasian toad. Larvae reared under 24-hour lighting had the longest development before metamorphosis. In other variants, the duration of larval development was similar; however, the lowest values of this indicator were in the group with a photoperiod of 12 hours. The larvae demonstrated high survival under all illumination options; however, it was maximal in the complete absence of illumination, and minimal, with a photoperiod of 12 hours. The largest were toads raised under 24-hour lighting. All other groups did not differ in terms of size characteristics. The highest feed costs for growing one larva before metamorphosis were under 24-hour illumination, and the lowest – in the dark and under 6-hour illumination. The feed costs per animal were similar in other groups. For an increase in 1 g of toad weight after metamorphosis, most of all was spent on food in the group with a light period of 12 hours, and the least – with a photoperiod of 6 hours. Conclusions. It is recommended to use 6-hour daylight hours for growing the larvae of the Caucasian toad in the laboratory. During this photoperiod, the larvae had a relatively short period of development (46–58 days), high survival rate (88,9–100 %), body length (10,0–12,4 mm) and weight (0,10–0,20 g ) after the passage of metamorphosis, as well as low feed costs for growing one individual (0,196–0,216 g).

Keywords

• amphibians
• rare species
• conservation
• larvae
• daylight hours
• zoo culture