Spawning of rotan in the basin of the Amur River takes place at the end of May through June at a temperature of 15-20 at the age of 2+ - 3+ (i.e. on the third to fourth year) when body length is 5-6 cm (Kirpichnikov, 1945; Nikolsky, 1956). In aquarian conditions rotan can mature earlier at the second year of life (1+) (Makhlin, 1957) at the same sizes. In the European part of the acquired distribution range the majority of rotans mature at body length of 45-70 cm at the age of 2+, but there occur specimens having acquired maturity in the second year (1+) (Spanovskaya et al., 1964; Pronin, Litvinov, 1994). According to the data of Zaloznykh (1982, 1984) for Gorky Region females mature at body length of 4-5 cm and weight of 1.9-3.7 g, males become mature at a length of 3.4 cm and weight 0.95 g.
Analyzing literature data we can conclude that at more favourable temperature conditions in the acquired distribution range (a longer period of comparatively high water temperatures) duration of spawning period of the population increases and the number of portions laid by each separate female grows.
For the natural distribution range Kirpichnikov (1945) assumed one time spawning. The author emphasized that in relation to conditions of spawning rotan is hardy. He observed spawning in a water body with a depth of 30 cm, an area of 150 square m, which served as a reservoir of watering vegetable gardens, but was also polluted by cattle, was used for laundry and had hard water rich in chlorine and bicarbonate.
Reproduction of rotan in the acquired distribution range was studied in detail.
From the data of Spanovskaya and others (1964) for ponds of Moscow suburbs the spawning occurred in portions and was protracted as was shown by the observation (catch of larvae 6-7 mm in length in June and discovery of clutches of eggs, larvae, yearlings 6-30 mm in length on 8 July 1962) and the state of gonads.
In June fishes with both low and high gonado-somatic index (=coefficient of maturity in Russian literature) occurred. The high coefficient of maturity was observed in fishes ready for the first spawning; in newly spawned individuals it was low (up to 2%). Coefficients 2-4; 6-8%, larger than in the previous group were noted in fishes that had spawned earlier. The next portion of eggs was maturing. In a female 6.3 cm in length and 6.7 g in weight caught on 14th July 1962 on sections of gonads there were many unresorbed empty follicles that indicated recent spawning and also a relatively large number of oocytes constituting the next second portion of eggs that were to be released in the same year. The second portion included 380 eggs. In July percentage of fishes with low maturity coefficient (less than 2%) increased because the major mass of fishes had completed its spawning in the same year. Few individuals having maturity gonado-somatic index of 8-10% were to spawn in July. The prolonged spawning is determined not only by release of eggs in portions, but also by irregular maturation of gonads within the limits of spawning period of individuals spawning for the first time or repeatedly; it also shows the different quality of growth in connection with unfavourable conditions of feeding of the population.
Smaller (younger) individuals seem to spawn only once (Manteifel, Bastakov, 1986).
Zaloznykh (1984) emphasizes that prolonged spawning in rotan defines the wide size composition of yearlings, and the varied quality of the young allows the species to use the water body more completely and, therefore, to increase its abundance.
According to the data of Pronin and Litvinov (1994) in rotan from Lake Gusinoye (Lake Baikal basin) the interval between the first and the second egg release is 14-18 days.
According to the data for ponds of Gorky Region (Zaloznykh, 1982, 1984) (we have not found such data for the native range) the number of fish eggs in clutches is 1155 to 13650, on the average 3700. As a rule several females lay eggs in the nest in turns. Quite frequently clutches of eggs on different developmental stages occur. Maximum difference in time of hatching of larvae from mixed clutches is equal to 4 days. Probably this period determines the time during which the male allows females to approach the clutch for spawning. An average number of eggs per portion ready for release fluctuates from 330 for females 4-5 cm long to 11,493 for females 13-14 cm long. Maximum number of eggs per portion, i.e. 17,874 is noted in a female 13.4 cm long.
Histological studies of gonads of rotan in a native range (Kurdyayeva, 1976) and in an introduced range (Travkina, 1997) have shown highly asynchronous development of oocytes and spermia, which provides a wide range of the number of laid portions.
Eggs are laid in even rows and are firmly fastened to the substratum by a thin filament. One day larvae have body length of 5.6 mm and height of 1.2 mm. From the first minutes of life the larvae swim freely and are spread among coastal vegetation. Larvae are weakly mobile (Zaloznykh, 1982; Vechkanov, 2000; Bolonev et al., 2002; et al.,).
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