The full-length Δ6FAD cDNA of mirror carp (Cyprinus carpio) was cloned by reverse transcript PCR (RT-PCR) and rapid amplification of cDNA ends (RACE) to study the regulatory role of Δ6 fatty acid desaturase in the biosynthesis of highly unsaturated fatty acid (HUFA). The cDNA for Δ6FAD gene was 1 446bp in full length including an ORF of 1 332 bp encoding a peptide with 444 amino acids (accession no.KJ576791). The protein sequence contained all the characteristics of microsomal fatty acid desaturases, including 3 histidine boxes, 2 transmembrane regions，and a cytochrome b5 domain．The protein sequence was characterized by microsomal fatty acid elongases and sharing 69% ~92.0% sequence identity with the Δ6 desaturase gene in other fish. The phylogenetic tree showed that it clustered closely into freshwater fishes. The expression of the enzyme gene in different tissues of mirror carp was detected by real-time quantity PCR (RT-qPCR), the maximum in the heptopancreas, followed by muscle, and the minimum in blood. There was higher expression level of Δ6FAD in liver than in other tissues, Indicating that heptopancreas is the main tissue of HUFA biosynthetic mechanism, with the minimal expression level of Δ6FAD in blood. The findings will be helpful for clarifying the HUFA biosynthetic mechanism in mirror carp and for the development of method in enhancing such ability.

In this paper, thirty-two microsatellite markers were used to analyze DNA differences among of Amur sturgeon (Acipenser schrenckii), Kaluga (Huso dauricus) and their hybrids [H. dauricus (♀)×A. schrenckii (♂)]，in which 28 were amplified in the three species, and one was merely amplified in Amur sturgeon, and three were not be applied well in Kaluga. Results showed that there were five markers which were effectively identified in the three populations, among which the amplification products of HLJSX350 was 227 bp in Amur sturgeon, 209 bp in Kaluga, and a mixed band of 209 bp and 227 bp in their hybrids. In addition, the specific loci from a part of Amur sturgeon and Kaluga were distinguished effectively in the amplification products of HLJSX226, HLJSX329, HLJSX332, and HLJSX351. Therefore, combining part of those loci can effectively be used to identify those three species of sturgeons. These co-dominant markers provide a powerful tool to identify the sturgeons and conserved species.

Nile tilapia Oreochromis niloticus juveniles with body weight of (9.81±0.42) g were reared in 20 150L recirculating tanks at a rate of 15 individuals per tank and fed isonitrogenous and isolipid diets containing amylose-amylopectin ratios of 0.10 (diet 1), 0.24 (diet 2), 0.47 (diet 3), 0.76 (diet 4) and 0.98 (diet 5) at water temperature of 27.5~32℃ with four replicates over a 6-week period to evaluate the responses of growth and intestinal microbial fermentation to starch type. It was found that the fish fed diet 2 exhibited the maximal weight gain and feed efficiency, significantly higher than the fish fed diets 4 and diet 5 did, and the minimal performance in the fish fed diet 5. The number of intestinal bacteria Escherichia coli and Lactobacillus spp. was shown to be elevated as the dietary amylose-amylopectin ratio was increased. There was significantly higher digesta acetate concentration in the fish fed diet 5 than that in the fish in the other groups, and there was significantly higher digesta propionate value in the fish fed diet 3 that those in the fish fed diets 1, 4 and 5. However, no digesta butyrate was detected in digesta of the fish fed various diets. The fact that there was inconsistent relationship between growth and bacterial fermentation in the fish fed various dietary amylose-amylopectin ratios leads to further investigation to better understanding of starch metabolism associated with nutrient utilization in the fish.

The individual fecundity was studied in minnow Phoxinus lagowskii Dybowskii collected in Suifen River in Heilong River Valley, and the relationship between the individual fecundity and the biological indices were evaluated to understand the reproductive biology of the minnow. The results showed that the minnow had average absolute fecundity of 6738.50 eggs/fish, range from 1636.67 eggs/fish to 11623.33 eggs/fish，heavily distributed in the range of 5000~9000 eggs/fish. And the average relative fecundity of 74.39 eggs/g body weight, range from 37.03 to 95.35 eggs/g, and heavily distributed in 50~90 eggs/g. The individual relative fecundity in body length was ranged from 109.30 to 571.62 (average 360.08) eggs/cm, mainly in 250~450 eggs/cm. The absolute fecundity and relative fecundity in body length were found to be very significantly increased with the increase in body length, body weight, maturity coefficient, and condition factor (P<0.01). There was no significant relationship of the relative fecundity in body weight with body weight and condition factor (P>0.05), but with significant relationship of the relative fecundity in body weight with body length (P<0.05) and with very significant relationship of the relative fecundity in body weight with maturity coefficient (P<0.01).

Juvenile skin carp Hemibarbus labeo with body weight of 148.03±0.28g was reared in net cages of each 6 m×12 m×3.5 m disposed in a reservoir at a rate of 1500 individuals per cage and fed 5 iso-protein and lipid diet containing various carbohydrate levels (25.3%, 29.2%, 33.3%, 37.1%, and 41.6%) with triplication at water temperature of 21.6℃ for 60 days. It was found that survival was not significantly affected by the dietary carbohydrate levels (P>0.05). However, the daily weight gain and specific growth rate were shown to increase first and then to decrease as the dietary carbohydrate level was increased, significantly lower final body weight of the fish in the 41.6% dietary carbohydrate group that that in 29.2%, 33.3% and 37.1% dietary carbohydrate groups (P<0.05), without significant difference between 41.6% dietary carbohydrate group and 25. 3% dietary carbohydrate group (P>0.05). There were no significant differences in feed conversion rate and protein efficiency in 33.3%, 37.1%, and 41.6% dietary carbohydrate groups (P>0.05), but significant differences between 25.3% dietary carbohydrate group and 29.2% dietary carbohydrate group, indicating that dietary carbohydrate level of 33.3%~37.1% is the optimal for growth and feed utilization of skin carp juveniles.