Organ Development, Nutrition Metabolism And Energy Budget During The Early Development Of Odontobutis Potamophila (Gǖnther)

The Odontobutis potamophila (Günther) belongs to Perciformes, Odontobutidae. It is an important freshwater commercial fish in china. So far, some researches had been carried on in Odontobutis potamophila (Günther), especially in the embryonic, larval and juvenile development as well as the feeding of larva, juvenile and fry. The present paper, more studies on organ development, nutrition metabolism and energy budget during the early development of Odontobutis potamophila (Günther) were carried on. The main results are concluded as follows:1. Visual organ development and its relationship with feeding of Odontobutis potamophila (Günther)The visual organ development of Odontobutis potamophila (Günther) was examined with microscopy, the relation between visual development and feeding was also studied. The main results are listed as follows. The optic vesicle was of neuroectodermal origin. At the heart-beating stage, the optic vesicle folded and formed the optic cup. Soon afterwards, optic cup induced the overlying surface ectoderm to form the lens, and it proliferated into the retina. During the development, the lens diameter increased, and the lens gradually developed to be perfect. At the eye pigmentation stage, the retina differentiated into six layers. Outer nuclear layer, inner nuclear layer and ganglion cell layer were observed. At the prehatching stage, the retina was composed of ten layers. One day after the hatching, the retina had become functional and larvae gradually began to feed. The thickness of the retina increased and the structure developed to be perfect with the development. The structural and visual characters of the retina indicated that Odontobutis potamophila (Günther) was diurnal species with good vision. 2. Ontogeny of the digestive system and variations in digestive enzymes activities during early development of Odontobutis potamophila (Günther)Ontogeny of the digestive tract and accessory glands in Odontobutis potamophila (Günther) was morphologically and histologically examined using light microscopy during the early development. Activities of digestive enzymes were also analyzed during the embryonic and larval development of Odontobutis potamophila (Günther). The main results are listed as follows. At the blood circulation stage, the digestive tract appeared and it was a simple undifferentiated tube. At the swim bladder formation stage, the mouth opened and the esophagus was present, the digestive tract began to curve and the liver was obvious. At the prehatching stage, jaw teeth, goblet cells and taste buds appeared, the stomach was differentiated. Longitudinal folds of the stomach epithelium could be seen, which gradually became more and more prominent. The intestinal convolution and the pancreas also appeared. The digestive tract was distinctively divided into buccopharyngeal cavity, esophagus, stomach, anterior intestine and posterior intestine at 1-2 days after hatching (DAH) coinciding with the time of first feeding. The stomach was divided into cardiac, fundic and pyloric regions. The gall bladder was obvious. Gastric glands distributed in fundic regions at 5-8 DAH. At this stage, supranuclear vacuoles occurred in the anterior intestine and eosinophilic granules occurred in the posterior intestine. The volume of the liver increased. Zymogen granules were seen in the exocrine pancreas and the langerhans was obvious. From 21 DAH to 33 DAH, the digestive system developed to be perfect. Important variations in activities of main digestive enzymes were observed during the embryonic and larval development. It was suggested that the activities of the digestive enzyme were associated with morphological changes of the digestive system during the embryonic and larval development.3. The development of the hatching gland and the secretion of hatching enzymein Odontobutis potamophila (Günther)The development of the hatching gland and the secretion of hatching enzyme in Odontobutis potamophila (Günther) were examined with microscopy and scanning electron microscopy (SEM). The hatching gland with monolayered cells originates from the ectoderm. The hatching gland (HG) appeared first at the stage of lens formation. The hatching gland cells (HGCs) were located in the ventral part of the head and in the joint region between the head and the yolk sac. The HG with monolayered cells was still distributed on the outer surface of embryonic body and yolk sac, the number and the volume of HGCs increased significantly, HGCs spread more widely with the development of the embryo. When the embryo reached the eye pigmentation stage, the number of HGCs reached about 900—1 200. HGCs were located in the lateral parts and the ventral part of the head, the joint region between the head and the yolk sac, the anterior part and the ventral part of the yolk sac. The HGCs in Odontobutis potamophila (Günther) were oval, the short diameter was 5—8 μm and the long diameter was 7—12 μm. HGCs were darkish pink when stained with eosin. The hatching enzyme was formed in the HGCs at the stage of lens formation and accumulated until the prehatching stage. When the embryo reached the prehatching stage, the hatching enzyme granules were secreted into the perivitelline space from the top of HGCs. Secretory granules were spherical and 0.5—1.0μm in diameter. The hatching enzyme was dissolved in the perivitelline fluid, where it gained access to the egg envelope and digested the inner layer of the egg envelope. The outer layer remained like a fragile veil that was then broken by the embryo. HGCs disappeared from epidermis about 2 days after hatching.4. Changes in the protein content and amino acid pool during embryonic and larval development of Odontobutis potamophila (Günther)The content of protein as well as the composition and content of amino acids were measured and analyzed during the embryonic and larval development of Odontobutis potamophila (Günther). The results indicated that the content of total proteins and total amino acids were all decreased with the embryonic and larval development. Overall, the changes in the total essential amino acids (TEAA) and the total non-essential amino acids (TNEAA) reflected that of the total amino acid pool. Qualitatively, the predominant amino acids were leucine, lysine, glutamic acid and aspartic acid during the embryonic and larval development. In contrast, the free amino acids (FAA) pool increased with development, the changes being reflected in both the free essential amino acids (FEAA) and the free non-essential amino acids (FNEAA). Throughout development, the FAA accounted for only a small proportion (0.16% in fertilised eggs) of the total amino acid pool. Because the egg protein and the total amino acid contents declined with development, it was concluded that the rate of breakdown of yolk protein was higher than the anabolic and catabolic processes during embryogenesis. Data also suggested that FAA was an unlikely primary energy substrate during embryogenesis in freshwater fish.5. Variation in the lipid content and fatty acid composition during embryonicand larval development of Odontobutis potamophila (Günther)The content of lipid and the composition of fatty acid were measured and analyzed during the embryonic and larval development of Odontobutis potamophila (Günther). The results indicated that the content of total lipid decreased during the embryonic and larval development. Saturated fatty acids (SFA) also decreased with development. Monounsaturated fatty acids (MUFA) remained stable during embryonic development, which decreased significantly during larval development. Polyunsaturated fatty acids (PUFA) increased significantly with development. The fatty acids that occurred in the highest abundance in all developmental stages, in order, were C16:0, C18:ln-9, C18:0, C16:l, C22:6n-3 (DHA) and C20:5n-3 (EPA). The ratios of DHA/EPA and AA/EPA in fertilized eggs were approximately 1:1 and 1:2, respectively, and remained almost unchanged during embryonic development, and both which was approximately 2:1 during larval development. Overall, there was a tendency to consume saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA), and conserve n-3 and n-6 series highly unsaturated fatty acids (HUFA). Saturated fatty acids (SFA) were utilized as energy substrates during embryonic development, and monounsaturated fatty acids (MUFA) were utilized as energy substrates during larval development, C18:3n-3 (linolenic acid) and C18:2n-6 (linoleic acid) were utilized to synthesize DHA, EPA and AA.6. Effect of salinity on the energy budget during embryonic and larval development of Odontobutis potamophila (Günther)In freshwater and the salinities were 1.00, 2.00, 3.00 and 4.00, respectively, oxygen consumption rate and NH3-N excretion rate were measured during embryonic and larval development of Odontobutis potamophila (Günther). The energy conversion during embryonic and larval development of Odontobutis potamophila (Günther) was studied at different salinities. The main results showed that the effects of salinity on oxygen consumption rate and NH3-N excretion rate were significant in different development stages, the oxygen consumption rate at 1.00 salinity was the minimum, the NH3-N excretion rate increased gradually with increasing salinities. The effects of salinity on energy budget during embryonic and larval development of Odontobutis potamophila (Günther) were also significant. The pattern of energy allocation at 1.00 salinity was the best pattern, the proportion of food energy allocated metabolism (R/C) was the minimum (35.06%), and the proportion of food energy allocated growth (G/C) was the maximum (58.55%). At 1.00 salinity, the mean equation of energy budget was 100C=6.40U+35.06R+58.55G.7. Effect of salinity on the biochemical composition and energy budget in starved juvenile Odontobutis potamophila (Günther)In freshwater and the salinities were 1.00, 2.00, 3.00, 4.00, and 5.00, respectively, the biochemical composition and NH3-N excretion rate in starved juvenile Odontobutis potamophila (Günther) were measured and analyzed. The energy conversion during starvation was studied at different salinities. The main results showed that the effects of salinity on biochemical composition and NH3-N excretion rate in starved juvenile Odontobutis potamophila (Günther) were significant, the loss of dry weight at 2.00 salinity was the minimum, and the protein and lipid consumptions were also the minimum. The NH3-N excretion rate increased gradually with increasing salinities. The effects of salinity on energy budget in starved juvenile Odontobutis potamophila (Günther) were significant, too. The pattern of energy allocation at 2.00 salinity was the best pattern, the growth energy loss of starved juvenile fish was the minimum, it was 13.295J, and the proportion of growth energy allocated metabolism was the minimum, it wasll.940J. At different salinities, the equations of energy budget are listed as follows.freshwater 7.51U+92.49R-100G=01.00 9.80U+90.20R-100G=02.00 10.23U+89.77R-100G=03.00 8.66U+91.34R-100G=04.00 10.16U+89.84R-100G=05.00 7.85U+92.15R-100G=0...