Gao Tianxiang

Effects of temperature, pH and NaCl on protease activity in digestive tract of young turbot,Scophthalmus maximus

The protease activity in digestive tract of young turbotScophthalmus maximum was studied, and the optimal pH, temperature and NaCl concentration were determined for different portions of the fishs internal organs. The optimal activity in the fishs stomach was at pH of 2.2, while that in the intestinal extracts was within the alkaline range from 9.5 to 10.0. In hepatopancreas, the optimal pH was in low alkalinity at 8.5. The optimal reaction temperature was above 40°C in stomach, intestine and hepatopancreas. With increasing temperature, the pH value increased in stomach, while in the intestine, an opposite tendency was observed due to combined effect of pH and temperature. NaCl concentration showed inhibitory impact on protein digestion in hepatopancreas. The main protease for protein digestion in turbot seemed to be pepsin. Moreover, the maximum protease activity in different segments of intestine existed in the hindgut.

Histological study on the digestive system development ofTakifugu rubripes larvae and juvenile

The digestive tract ofTakifugu rubripes during early life stages was studied with light microscopy. At the beginning of hatching, the digestive tract is represented by a simple and undifferentiated straight tube and does not communicate with the exterior, as the mouth and anus are not open yet. At 2 d after hatching, a constriction between intestine and rectum that will become the intestino-rectal valve is visible. During the endogenous feeding phase, the yolk sac is resorbed and the digestive tract becomes functional and differentiated. The liver and pancreas also become apparent at this time. At onset of exogenous feeding (3 d after hatching), yolk sac resesves are not completely depleted, suggesting a period of mixed nutrition. The digestive tract differentiates fully into buccopharynx, esophagus, stomach, intestine and rectum. At 9 d after hatching, the yolk sac reserves are completely depleted. The most noticeable events occurring from 5 to 17 d after hatching are the transformation of the epithelia type, the differentiation of the pneumatic sac, the epithelial cell, gut convolution, mucosal fold increase, and the growth of liver and pancreas. From 18 to 27 d after hatching, the numbers of intestine folds and mucus cells increase progressively. From then on, morphological changes of digestive features are almost completed. At 27 d after hatching, the morphology and function of digestive system are similar to that of the adult.

Structure and Dynamics of Fisheries in Nigeria

The changes that have taken place in Nigerian fisheries are reviewed. Artisanal fishery has continued to dominate the fisheries, contributing over 85% of total fish production. The inland water and coastal seas are fully exploited and the increase in fishery production is not likely. Aquaculture potentials remain untapped as much as deep-sea fisheries. The combined potential of the fisheries resources-freshwater, marine and aquaculture can meet over 90% of the nation’s demand for fish. Opportunities for investments, therefore, exist in the various subsectors, especially in the areas of storage, processing and preservation for the capture fishery and fish seed multiplication for aquaculture.

A comparative study of Sepia esculenta and Sepiella maindroni on embryonic development and ability of salinity tolerance

Fertilized eggs of Sepia esculenta and Sepiella maindroni were collected from the wild and the embryonic development of S.esculenta was observed in laboratory.The morphological characters of fertilized eggs and newly hatched larvae between the two species were also compared.The effects of different seawater salinities of 20,25,30 (control),33,36 for S.esculenta and 15,20,25,30 (control),36 for S.maindroni on hatching rate were studied,respectively.Changes in egg fluid osmolality and egg Na+/K+-ATPase activity of S.esculenta and S.maindroni were also measured during the abrupt salinity changes of 192 h,respectively.Hatching rates of fertilized eggs at the same salinity and physiological adaptation to the abrupt salinity changes during 192 h were compared between S.esculenta and S.maindroni.The results showed that organ differentiation happened when embryo was 7-day-old,while organ formation occurred when embryo was 14-day-old for S.esculenta.The incubation period of S.esculenta fertilized egg ranged from 21 d to 22 d at 22-24 ℃ and salinity of 30.Hatching rates of S.esculenta and S.maindroni under control treatment were significantly higher than those under other salinity treatments (P0.01),indicating that salinity of 30 was the suitable hatching salinity for fertilized eggs of the two species.Fluid osmotic pressure of S.esculenta and S.maindroni fertilized egg changed as seawater salinity altered during the abrupt salinity change.The egg fluid osmotic pressure of S.esculenta was equal to the medium osmotic pressure,while the egg fluid osmotic pressure of S.maindroni was 60 mOsm/kg higher than those in the medium.Activities of Na+/K+-ATPase were not found in fertilized eggs of two species.These results indicate that fertilized eggs of two species have little ability in regulating osmotic pressure.However,fertilized egg of S.maindroni can accommodate salinity alteration better than S.esculenta.

Isozyme analysis on the populations ofRuditapes philippinarum

Horizontal starch gel electrophoresis was used to investigate the genetic structure of six populations ofRuditapes philippinarum in the coast of China. Seven enzymes revealed eleven putative loci, and seven of them were polymorphic,PGM*, MDH-1*,MDH-3*,LAP-1*,LAP-2*,MPI-1* andMPI-2*. The proportions of polymorphic loci ofR. philippinarum populations varied from 0.454 5 to 0.636 4. The values of observed and expected heterozygosities were from 0.039 4 to 0.154 5 and from 0.1111 to 0.2385, respectively. Neis genetic distance varied from 0.003 3 to 0.025 3 with an average of 0.013 5. It is suggested that the genetic diversity ofR. philippinarum was high.

Comparative analysis of the mitochondrial control region between the cultured and wild populations of Chinese shrimp (Fenneropenaeus chinensis).

In present study,genetic differentiation of the Chinese shrimp Fenneropenaeus chinensis between cultured( 21 individuals) and wild populations( 14 individuals,sequences were downloaded from the GenBank) was investigated using the sequence of mitochondrial control region ( CR ) .Four individuals of the F.merguiensis were chosen as the outgroup during the phylogenetic analysis in this study.Sequences were edited and aligned using DNA Star software and refined manually.Genetic diversity indices such as number of haplotypes,polymorphic sites,transitions,transversions,and indels were obtained using the program ARLEQUIN( Ver.3.0) .Haplotype diversity( h) and nucleotide diversity( л) were calculated with DNASP 4.0.The nucleotide compositions and the average distances between populations and within population were calculated with MEGA 4.0.The Network software was used to draw the minimum spanning tree based on the haplotype data.The results were as follows:the A + T content was higher than the G + C content in both the populations,but the G + C content was a little lower in the cultured population.The results indicated genetic divergence existed between the 2 populations based on the 563 bp sequences.The gene diversity of the wild population( 0.967 2) was a little higher than the cultured population( 0.938 0) .There was no shared haplotype between the 2 populations.The ratio of transitions/transversions of the wild populations and nucleotide diversity were 3.5 and 0.010 6 respectively while they were 4.0 and 0.009 4 for the cultured population.The nucleotide diversity of the wild population was a little higher than cultured population.The K-2P distance was 0.010 8 between the 2 populations,0.010 7 in the wild population and 0.009 5 in the cultured population.Both the NJ phylogenetic tree and the haplotype minimum spanning tree showed no significant genealogical structure.The exact test of population differentiation showed that the 2 populations were significantly different ( P=0.000 9) .The FST value between the populations was 0.069 8( P=0.00) ,which indicated that the difference between 2 populations was significant.This may indicate that some alleles were lost during the aquaculture.

Development of retinal structure and visual acuity in Japanese flounder (Paralichthys olivaceus)

The retinal structure and visual acuity in Japanese flounderParalichthys olivaceus at different stages of development were examined by light microscopy. The resolving power of the retina, the visual axis and the best visual field were estimated based on the distribution of cone cells in the retina. The visual system of the larvae appears poorly developed at hatching. The larvae with total length (TL) of less than 10 mm, have single cones only and the eyes were well pigmented. At 10–11 mm TL, most single cones fused to form double cones, with the single and double cones forming a mosaic pattern. From larvae to early juvenile the retina stretches, the cones increase in diameter and rods increase in number. Based on the highest density of the cones in the ventro-temporal region, the visual axis was orientated upforward. The resolving power of the retina in 40–530 mm TL Japanese flounder was found to range from 25.1 to 11.5 min. The results indicated continual improvements in the visual system of the growing fish towards higher resolving power, visual acuity and sensitivity.