Abstract
The clownfishes,or sea anemonefishes,of the genus Amphiprion and Premnas with approximately 30 species,belong to the Subfamily Amphiprioninae,the Family Pomacentridae.Many clownfishes are popular in the tropical marine ornamental fish trade.In recent years,the clownfishes remain the Ranking One in the trade based on the estimated annual amount of individuals sold.Hatchery-based larviculture and grow-out of clownfishes have been developed in several countries.In China,at least six species can be hatchery-produced and grown up to marketable sizes of 3—5 cm total length,including Yellowtail clownfish A.clarkii,Tomato clownfish A.frenatus,Orange clownfish A.percula,Pink Skunk Clownfish A.perideraion,Saddleback clownfish A.polymnus and Maroon Clownfish P.biaculeatus. Metabolic rate indicates the efficiency of food and energy intake,conversion and allocation,and is influenced by fish body condition and environmental factors.Respiration and excretion are the two main components of metabolism.Respiration rate can be calculated through the measurement of total oxygen consumption,and excretion rate can be calculated through the measurement of total ammonia nitrogen excretion.Based on the oxygen/nitrogen ratio,the energy sources that fish utilized mainly for somatic growth can be determined. This study was conducted to investigate the effects of water temperature and body weight on respiration and excretion of Yellowtail clownfish Amphiprion clarkii during its larval development from newly-hatched to the complement of metamorphosis.Larvae were reared at three water temperatures of 23,26 and 29℃ in captivity.Individual respiration rate(RR,μg O2 ind-1 h-1) and individual total ammonia nitrogen excretion rate(ER,μg N ind-1 h-1) of A.clarkii were measured,respectively.The results showed that RR and ER increased with body weight(W,mg) as a power function of R = aWb at all three water temperatures.The b-values were 0.8873,0.9033 and 0.9323 for RR,and 0.7625,0.8012 and 0.8278 for ER,at 23,26 and 29℃,respectively.RR and ER at 29℃ were significantly higher than those at 23 and 26℃(P0.01).Multiple regression analyses showed the variability in the integrated effects of temperature(T,℃) and W on RR and ER: RR= 0.042W0.889×e0.122T and ER = 0.002W0.797×e0.115T.At the same water temperature,both respiration rate per body weight(RR′,μg O2 mg-1 h-1) and total ammonia nitrogen excretion rate per body weight(ER′,μg N mg-1 h-1) in larvae of A.clarkii decreased with the increase of W.With the increase of water temperature,RR′ and ER′ increased.RR′ and ER′ at 29℃ were significantly higher than those at 23 and 26℃(P0.05).The oxygen/nitrogen ratios(O/N) in larvae of A.clarkii were around 52-57 at all three water temperatures,and showed no difference(P0.05),indicating that the main energy sources for larval development are protein,fat and carbohydrate.High temperature effects(Q10) for both respiration and excretion were found over the water temperature range of 23—26℃,with 3.70 and 4.01,respectively.Low Q10 for respiration was found at 26—29℃ with a value of 2.40,and low Q10 for excretion was found at 23—29℃ with a value of 2.5.This study reveals that the optimal water temperature for larval development of A.clarkii lies between 26 and 29℃.
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