Effects Of Delayed First Feeding On Morphology Characteristics, The Energy Content, And Swimming Performance Of Southern Catfish (Silurus Meridionalis Chen) Larvae

Southern catfish (Silurus meridionalis Chen) is a warmwater fish, spawns inearly spring. It is widely distributed in the Yangtze and Zhujiang Rivers where theabundance of its food fluctuates dramatically during the year. It was widely used as anexperimental model for fish ecophysiology study. The effects the timing of initialfeeding (4, 5, 6 and 7days post-hatch, dph) on morphology characteristics, energycontent, and swimming performance of artificially fertilized southern catfish larvaewere conducted at 22.0 ± 0.5℃ in the Laboratory of Evolutionary Physiology andBehavior of Chongqing Normal University.Larvae were sampled for initial body length, head length, length behind anus,head width, body mass and energy content at 4dph. Then the larvae were fed for thefirst time at 4, 5, 6 and 7 dph. The the critical swimming speed, body length, headlength, length behind anus, head width and body mass and energy content of larvaewere measured and relative fatness was calculated at 7 dph in both feeding andnon-feeding groups, and the critical swimming speed, body weight, body length andthe energy content of feeding groups were measured at 21 dph respectively.The results showed that the length, head length, length behind anus and headwidth of feeding groups measured at 7 dph significantly decreased from 17.03±0.15mm,3.20±0.05mm,9.63±0.12mm,3.06±0.05mm to 12.00±0.11mm,2.28±0.03mm, 6.76±0.10mm,2.60±0.05mm, respectively(p<0.05). The morphologyparameters showed significant variation among experiment treatments (p<0.05).The parameter measured at 21 dph showed that the body weight, energy contentand body length of larvae first fed at 5, 6 and 7 dph gradually approach those of larvaefirst fed at 4 dph. There is no significant difference of body length between larvae firstfed at 4 dph and 5 dph.The body length, weight and energy content specific growth rate had a tendencyto decrease with increased delayed first feeding time at 7 dph, but had an oppositionaltendency at 21 dph.At 7 dph, the relative critical swimming speed of larvae which was first fed at 6dph was higher than other groups, but no significant difference in absolute criticalswimming speed was found among different experimental groups except for larvaefirst fed at 7dph. Two weeks later, no significant difference was found among differentexperimental groups except for larvae first fed at 7dph in both the relative criticalswimming speed and the absolute critical swimming speed.The correlation between the relative fatness (R) and first feeding time delayed (d)could be expressed as: R=0.046 e-0.468d (n=15,r=0.788,P<0.01), and the correlationbetween the relative critical swimming speed and body length of the control groupcould be expressed as Ucrit =2.22L + 6.93 (n=75, r2=0.367, p<0.01)The results indicated that in Silurus meridionalis Chen, the negative growth ofbody mass did not prevent the development of southern catfish larvae. The bodylength was more inflexible compared with body energy content and more flexiblecompared with the swimming performance when facing the temporal patchiness offood availability during the early development stage.