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The Pearl River Estuary is the largest estuary in South China and plays a considerable role in the local fisheries economy, yet little is known about the current state of fish assemblage in this ecosystem. To quantify spatial‐seasonal variations, environmental influences, and trends over the past three decades of the fish assemblage in the Pearl River Estuary, we sampled 11 sites seasonally from December 2013 to September 2016. Throughout the study, 285 species from 88 families and 195 genera were collected. There were obvious spatial and seasonal variations of the fish assemblage in terms of the dominant species, species richness, and composition of ecological types. Mouth distance, NH4+ N, chlorophyll‐a, flow, DO, salinity and water transparency were the main variables influencing the spatial‐temporal dynamic of fishes within the estuarine systems. Compared with the record of 330 species in the 1980s, the number of fish species in the Pearl River Estuary has declined by 45 fish species. The Jaccard's similarity of fish composition between the historical investigation (the 1980's) and the present investigation (2013–2016) was 0.62, with 95 species undiscovered and 50 species increased in the present study compared to the 1980s, indicating the assemblage structure has obviously changed. However, in term of ecological guilds, there was no significant difference in the composition of all the selected ecological traits between these two periods. Anthropogenic activities including overfishing, introducing alien fish, dam construction and pollution were considered the main disturbance on fish composition over the past three decades. We conclude that there existed pronounced spatiotemporal changes of fish assemblages, which arises from the compounding effects of environmental factors and anthropogenic activities. These findings are beneficial to understanding and developing suitable conservation strategies for the management and protection of fish resources in the Pearl River Estuary. [ABSTRACT FROM AUTHOR]

This works studies the physiological characteristics (sperm motility characteristics) and biochemical characteristics (DNA damage, enzymes activities and fertilization ability) of fresh and freeze-thawed semen of sex-reversed female mandarin fish Siniperca chuatsi (n = 30) obtained with the application of 17α-methyl testosterone for sex reversal. The fresh sperm motility and fertilization rate of sex-reversed females were about 83% and 70% respectively which had no significant difference with normal males (p > 0.05). Except for the value of DNA damage, other values of sperm motility, related enzymes activities and fertilization rate of sex-reversed female sperm declined after a process of cryopreservation (p < 0.05). But the frozen sperm can still get nearly 60% of the fertilization rate. This study identified the physiological and biochemical characteristics of the fresh and cryopreserved sperm from sex-reversed female mandarin fish, and the sex-reversed female spermatozoa can be used for actual production. • The biological characteristics of the sperm from the sex-reversed females show similar physiological characteristics to male mandarin fish. • The sperm of the sex-reversed female mandarin fish can be successfully cryopreservation. • The biological function of frozen sperm from the sex-reversed females has been impaired, but it can still be used for artificial propagation. [ABSTRACT FROM AUTHOR]

All-female populations of mandarin fish (Siniperca chuatsi) provide economic advantages in production because of the superior growth of females relative to males. The first step to produce all-female populations was artificially induced sex reversal of female mandarin fish; beginning at 10 dph, fish (undifferentiated) were treated with dietary 17α-methyltestosterone (MT) at 50 mg/kg and 100 mg/kg dosages for 2 months. The MT treatments successfully produced all-male stocks (male rate 100%), as compared with the control group (51.11%). The survival rate of MT-treated and control groups was not significantly different. MT did not alter fish growth over the course of the experiment to 240 dph. MT treatment promoted the development of testes, and it initially inhibited gonadosomatic index (GSI) and the levels of serum steroid hormone (T and E2). Nevertheless, at the 180 dph and 240 dph, the GSI and serum steroid hormone (T and E 2) levels in MT treatment groups had no significant difference with control groups. The masculinization of mandarin fish was also demonstrated by the expression patterns of sex-specific genes, dmrt1, sox9, foxl2 and cyp19a1a ; the gonads of MT-treated fish exclusively expressed male-specific dmrt1 and sox9 with no expression of female-specific foxl2 and cyp19a1a. • 17α-methyltestosterone worked well to produce neomale mandarin fish. • The growth, GSI and serum steroid hormone (T and E2) levels of MT-treated and control groups had no significant difference at the 180 dph and 240 dph, but the development of testis was promoted by MT. • Sex-specific genes further confirmed our results that MT can successfully induce sex reversal mandarin fish. [ABSTRACT FROM AUTHOR]

The mandarin fish, Siniperca chuatsi , is a kind of ferocious carnivorous fish, which has highly economic value with the characteristic of rapid growth and delicious flesh. Large scale industrial breeding of mandarin fish has been realized widely in China. The triploid in mandarin fish S. chuatsi had been induced by hydrostatic pressure shock. The most effective condition of triploidy induction was initiation of pressure treatment 6 min after fertilization, duration of treatment 2 min and magnitude of pressure 450 kg/cm2 in which could result in 72% triploid fish. There were no significant differences of the survival of triploid rates among the three treatment groups, which include holding for 4 min, 6 min, and 8 min after fertilization. The efficiency of triploidization was confirmed by counting the number of chromosomes and was affirmed by DNA content determination using flow cytometry with blood cells of one-month old fingerlings. The chromosome count of induced triploids was 3n = 72 while diploid fish had 2n = 48. The flow cytometry shows that DNA content in experimental group was 1.5 times as the control group. In conclusion, this paper presents optimal conditions for triploidy induction in mandarin fish with hydrostatic pressure shock, which will contribute to promote the progress of breeding industry and enhance the production of mandarin fish in culture. • This is the first report which is about the induction of triploidy by hydrostatic pressure shock in mandarin fish. • Triploidy induction was initiation of pressure treatment 6 min after fertilization, duration of treatment 2 min and 450kg/cm2 • The chromosome counting of mandarin fish reveals that 2n = 48 and 3n = 72. [ABSTRACT FROM AUTHOR]