| Macropodus opercularis, a 10-cm-long insectivore from Southeast Asia, is a teleost fish of the family Anabantidae native to fresh water habitats in southern China, Korea, and Taiwan,and lives in densely vegetated streams, shallow marshes and rice fields. The feeding rhythm under different photoperiods, prey selectivity, feeding intensity, and growth of Macropodus opercularis larvae were investigated, as well as the effect of population density on growth and survival of larvae. The results are showed as following:1.Feeding rhythm of larvae under different photoperiodsThe feeding rhythms of paradise fish, Macropodus opercularis, at the ages of 5d,8d, and 12d were determined under different light circumstances.The larvae of the three ages under natural photoperiod actively fed during 12:00-16:00. However, the larvae under successive light photoperiod and full dark photoperiod did not show up-and-down feeding rhythm. The larvae under successive lighting photoperiod actively fed all the day. Particularly, their feeding intensity was significantly greater than that under the natural light photoperiod from 20:00 to 4:00 in the next day. Conversely, the larvae under full dark photoperiod performed lower feeding intensity in contrast to those under the natural photoperiod, particularly during 8:00-16:00. It showed that the light conditions greatly influenced feeding activity of M. opercularis during their early life stages.2. Prey selectivity and feeding intensity of larvaeThe select index of M. opercularis larvae at the age of 2-6 days on copepod nauplius was greater than 0 (E>0), indicating that they favored the preys, and E<0 on rotifers indicated that they advoided to prey on rotifers.The larvae at the age of 7-11 days mainly feed on cladocera (E>0).Starting from 12-25 day after being born, M. opercularis larvae began feeding small copepods, while still preying on copepod nauplius and Cladocera as supplementary preys.375 larvae at different ages were dissected to observe the feed in the digestive tubes. M. opercularis larvae began to feed at the age of 2 day with the feeding ratio of 46.67%.During the whole larvae period (at the age of 2-25day), the average feeding ratio is up to 93.87%, and it reached 100% among the larvae after hatching 3 days. With the individual growth and development, the feeding ability of larvae was enhanced. The feeding amount of the 2-day larvae was only about 0.0017mg, and the average feeding amount of the whole larvae stage (at the age of 2-25day) reached to 0.136mg, with the average fullness index of digestive of 3.18%.3.Growth of larvaeAt the temperatures of 27～28℃,studies of growth of M. opercularis larvae have been conducted. The relationship between the total length (L/mm) and the age (D/d) was counted to be L=3.265e0.0526D (R2=0.9192), the relationship between the body mass (M/mg) and the age (D/d) could be expressed as M=0.3632e0.1755D (R2=0.8978), and the relationship between the total length (L/mm) and body mass (M/mg) was calculated to be M=0.0068L3.3326 (R2=0.9874).4. Effect of population density on growth and survival of larvaeM. opercularis larvae were reared in the tank at the densities of 50,100,150,200 ind/L for 15 days. The results showed that final weight, SGR and DWG of M. opercularis larvae decreased with the increasing of density. With the increasing of the population density, the survival rate of the larvae increased gradually. The mortality increased after population density reached the containable peak of 200 ind/L. |
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