Reproductive biology and factors affecting breeding in captivity of Rasbora daniconius

Abstract

Rasbora daniconius (Hamilton, 1822) is a relatively small fresh water minor cyprinid fish which very commonly dwells in lowland fresh water bodies in Sri Lanka. Present study was conducted to determine their reproductive biology and factors affecting breeding in captivity of this species. Relationships on length, depth and weight, length frequency distribution, percentage of females under natural conditions were determined. In the equation showing length-weight relationship (log Weight = log a + b log total length), ‘a’ and ‘b’ values for males were 6.93x1 O'6 and 1.2184 respectively. The ka’ and kb’ values for females were 7.77x1 O'3 and 3.1256, respectively. Also the ‘a’ and kb’ values for total population were 8.67x10"' and 3.0657 respectively. At higher length classes percentage of females was higher than the males and it reached 100% after 8 - 8.5cm length class. Length frequency distribution during the study (from April to July, 1997) shows the highest length for males and females are respectively 8.8cm and 10.7cm. In July the mature larger females disappeared from the sampling stations. In experiment on breeding in captivity, effect of plants and a false bottom, false bottom only, and plants only on the breeding of R. daniconius was studied. Control experiment was conducted without providing any one of the above conditions. After 37 days spawning was observed in tanks provided with plants and false bottom and with only false bottom. Mean GS1, Mean relative fecundity. Mean largest oocyte diameter and frequency distribution of oocyte diameter of experimental fish were determined before and after the experiment. However no significant difference were observed in above values in fish provided with different conditions (P > 0.05). Frequency distribution of oocyte diameter shows the highest frequency mode o f oocytes are consist of stage V and VI. Gonadal histological studies showed that in fish provided only with false bottom had migratory nucleus stage oocytes which are at the highest maturity stage. Testis also showed the spermatocytes at a higher developmental stage. In the ovaries in fish provided with other treatments yolk globular stage oocytes were abundant. Above results shows that the given environmental conditions do not affect significantly GSI, mean relative fecundity and the oocyte development of Rasbora daniconius, they have affected the spawning, and the false bottom has aided in the survival offish fry.