| In this paper, osteological development, structure of retina and teethdevelopment were examined in eggs and from newly hatched to33days old larvae ofSiniperca chuatsi. The results are as follows:Osteological development of neurocranium, suspensorium, upper and lower jaws,opercular apparatus, hyoid arch, branchial arch, vertebral column, paired and unpairedfins and their supports of S.chuatsi, was described from newly hatched larvae to33.86mm SL post-flexion larvae. Newly hatched larvae had little osteological element.Parts of cranial elements were formed in4.8mm NL, including the trabecula cartilage,ethmoid plate cartilaginous, they constituted the contour of the neurocranium togetherwith membranaceum on the dorsal region. Most osteological elements of upper andlower jaws, suspensorium and pectoral supports developed in4.8mm NL or smallersamples, these were the earliest development and ossification bones in larvae.Followed by opercular, hyoid arch, branchial arch which assisted larvae to completethe feeding activity successfully developed in5.2mm NL. Cartilaginous neural archesand haemal arches and caudal supports were present in6.4mm NL. Finally, the mostof cranial elements and pelvic supports observed and notochord became flexion in9.5mm NL larvae.The upper and lower jaws, opercular and pectoral supports were completelyossified in11.22mm NL. Preopercular developed many inner spines on its edge andthen became serrations in post-flexion larvae. Elongation in anterior process ofpectoral supports was a specialization for pectoral fins movement. S.chuatsi hadbasisphenoid and absent orbitosphenoid. Hyoid arch supports seven pairs rays and had ceratohyal foramen. There were two rows small teeth on ceratobranchials, and a rowgill rakers were only present on the first ceratobranchial. Epibranchials, lowerpharyngeal bones and upper pharyngeal bones had dense teeth over its dorsal surface.The centrum became partly visible at11.22mm NL and completely ossified at17.84mm SL. Ossification of centrum proceeded in a posterior direction but urostyleossified at first. Phy, Hy1and Hy2fused at9.5mm NL and then developed asseparate pieces, it’s because S.chuatsi had adapted to bottom life. Addition andossification of the neural arches and spines and haemal arches and spines proceededfrom anterior to posterior. Each neural arches and spines and haemal arches andspines ossified from the base and the end. Three pre-dorsal support no spines. Theformation of dorsal supports proceeded both anteriorly and posteriorly andossification in posterior direction which were the same as anal supports. Most of thebones had been completed ossified in26.91mm SL. The same with the mostteleostean, pelvic fins supports were the last to start developing. S. chuatsi larvaepossessed a large mouth and sharp teeth, vomer teeth, palatine teeth and pharyngealteeth. Active feeding behavior was attributed to the early ossification of feedingapparatus and the majority of teeth. The ossification of vomer, parasphenoid, bones ofotic and occipital regions and pectoral fin supports provides the neurocranium withstrength during movement and protects the brain from the pressures such as weight oftrunk. At44days after hatching, S. chuatsi larvae were similar to adult, but still noscales appear. From the view of osteology, we think that they were still in post-flexionstage.Paraffin section and HE section were adopted to examine the structure of theretina and visual characteristics of S. chuatsi fertilized eggs and from newly hatchedto30days old larvae. The main results obtained are as follows:(1)At54h afterfertilization, lens and undifferentiated retina had formed. At80h after hatching, theretina differentiated into four layers, including outer nuclear layer, inner nuclear layer,inner plexiform layer and ganglion cell layer. At98h, pigment epithelium, rods andcones layer and optic nerve fibers layer were observed. At124h, outer plexiform layerformed and the retina was composed of ten layers. At4days after hatching, a couple of jaw teeth and pharyngeal teeth appeared; At5days and14days, Palatine teeth andvomer teeth appeared respectively; At15days, gill rakers grew but small. In one word,the quantity of the teeth increased with the growth of larvae, until nearly the same asthat of the adult.(2) The structure of the inner nuclear layer of S. chuatsi have only alayer of horizontal cells, bipolar cells and amacrine cells, which shows that the retinaof S. chuatsi is not sensitive to light.(3) The teeth appeared before the maturity of thedigestive system in the S. chuatsi larvae, which serves to improve the success rate incatching prey. It is a full reflection of the adaptation of individual growth to theenvironment in its evolutionary process.(4)The quantity of the ganglion celldecreased with the development of S. chuatsi. At29days, the structure of theganglion cell layer of S. chuatsi decreased to a layer of ganglion cell indicates thatS. chuatsi larvae had adapted to the dark environment. It is revealed that the changesof visual structure of S. chuatsi are adapted to the ecological shift from pelagic tobenthic habitats and to the changes of feeding methods.The characteristics of skeletal growth and vision development in early period:Before hatched, the S. chuatsi larvae retina began differentiation54hours afterfertilization. Ten layers of the retina had developed completely and the feeding organsbegan to develop in4.8mm NL. At the same time, S. chuatsi began to prey, whichmeans it had entered the period of mixed nutrition. Thirty-three days after hatched,the hypurals had separated, illustrating it moves faster. It coincided with the featurethat S.chuatsi had adapted to the black environment29days after hatched. Histologicalobservation of the oral cavity teeth judged to be in conformity with skeletondevelopment. Osteological development in S.chuatsi provides basis scientificevidence for the classification of the fish. |
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