Comparative Mitogenome Analyses Uncover Mitogenome Features and Phylogenetic Implications of the Reef Fish Family Holocentridae (Holocentriformes).

To understand the molecular mechanisms and adaptive strategies of holocentrid fish, we sequenced the mitogenome of eight species within the family Holocentridae and compared them with six other holocentrid species. The mitogenomes were found to be 16,507-16,639 bp in length and to encode 37 typical mitochondrial genes, including 13 PCGs, two ribosomal RNAs, and 22 transfer RNA genes. Structurally, the gene arrangement, base composition, codon usage, tRNA size, and putative secondary structures were comparable between species. Of the 13 PCGs, nad6 was the most specific gene that exhibited negative AT-skews and positive GC-skews. Most of the genes begin with the standard codon ATG, except cox1, which begins with the codon GTG. By examining their phylogeny, Sargocentron and Neoniphon were verified to be closely related and to belong to the same subfamily Holocentrinae, while Myripristis and Ostichthys belong to the other subfamily Myripristinae. The subfamilies were clearly distinguished by high-confidence-supported clades, which provide evidence to explain the differences in morphology and feeding habits between the two subfamilies. Selection pressure analysis indicated that all PCGs were subject to purifying selection. Overall, our study provides valuable insight into the habiting behavior, evolution, and ecological roles of these important marine fish.

[Pollution by heavy metals in the petrochemical sewage waters of the sea area of Daya Bay and assessment on potential ecological risks].

This study aimed to gain a clear understanding on the status of pollution by heavy metals in the petrochemical sewage and the potential ecological risk caused by heavy metal pollution in the sea area of Daya Bay. The contents and spatial distributions of heavy metals including Zn, Pb, Cu, Cd, Cr, As and Hg in seawater, sediment and fishes collected from Daya Bay were analyzed. The comprehensive pollution index (CPI) and ecological risk indexes (ERIs) were used to evaluate the contaminated severity and potential ecological risks of heavy metals in seawater and sediment. The results showed that the contents of these heavy metals, except for those of Zn and Pb, in several stations set in Daya Bay from 2011 to 2012 were relatively low, which were lower than the quality standard of class I according to the China National Standard Criteria for Seawater Quality, suggesting that the seawater in Daya Bay has not been polluted yet by these heavy metals. The average CPI of heavy metals in seawater during flooding season (0.72) was higher than that during dry season (0.38) whereas the average CPI of heavy metals in sediment during dry season (7.77) was higher than that during flooding season (5.70). Hg was found to be the primary contaminating heavy metal in sediment during dry season, which was followed by As and Zn whereas during flooding season, Hg was the primary contaminating metal in sediment, followed by Zn and Cu. The contents of these 7 heavy metals in fishes collected from the surveyed areas were lower than those of the standard requirements. A correlation analysis indicated that there were significant differences in the correlations between the midst of the heavy metals in sea water and the different periods. The ERIs of heavy metals in sediment during dry season (129.20) was higher than that during flooding season (102.86), and 25% of the sampling sites among all stations were under the risk of high-level alarm. The potential ERIs of heavy metals in sediment in offshore waters were higher than those of inshore waters, and were higher in the bay-mouth than in the bay-head. However, the distributions of potential ERIs showed reversed trend during dry season. The comprehensive assessment results showed that Hg was the primary heavy metal with a high ecological risk whereas the potential ERIs for the other six heavy metals in the petrochemical sewage waters in Daya Bay were relatively low.

Dietary values of astaxanthin and canthaxanthin in Penaeus monodon in the presence and absence of cholesterol supplementation: effect on growth, nutrient digestibility and tissue carotenoid composition.

Penaeus monodon (mean initial wet weight 1·19 (SE 0·01) g) were fed seven diets in triplicate: a control diet (D1) without carotenoids; three diets formulated to supply 0·1 % astaxanthin alone (D2), 0·2 % astaxanthin alone (D3), and a combination of 0·1 % astaxanthin and 1 % cholesterol (D4); three diets with 0·07 % canthaxanthin alone (D5), 0·13 % canthaxanthin alone (D6), and a combination of 0·07 % canthaxanthin and 1 % cholesterol (D7). Weight gain (WG, %), specific growth rate (SGR, %/d) and survival were chosen as parameters of shrimp growth performance. Total antioxidant status (TAS), superoxide dismutase (SOD), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were chosen as indices of shrimp plasma antioxidant capacity. Meanwhile, digestibility, retention efficiency and tissue carotenoids were also investigated to determine the additive effect of cholesterol on the efficiency of astaxanthin and canthaxanthin. After 74 d rearing, WG and SGR of shrimp fed D2-D4 and D7 were higher than those of shrimp fed D1 (P < 0·05). Shrimp fed D4 had the highest survival. The apparent digestibility coefficients (ADC) of astaxanthin in D2-D4 were higher than those of canthaxanthin in D5-D7 (P < 0·05). Although ADC of astaxanthin were quite high (>98 %) in D2-D4 and no differences were found among them (P>0·05), the carotenoid retention efficiencies in the whole body, muscle and shell (D2-D3 treatments) were considerably low; however, cholesterol supplementation significantly improved the carotenoid retention efficiencies in the whole body, muscle and shell (D4 treatment). Accordingly, the addition of cholesterol also significantly enhanced the carotenoid contents of tissues. Shrimp fed supplemented carotenoid diets (D2-D7) had higher TAS and lower SOD, ALT and AST than shrimp fed D1 (P < 0·05). A low dissolved oxygen stress test was conducted for 7 d after the rearing trial and shrimp survival was also compared among the treatments. The survival of shrimp fed the diets supplemented with astaxanthin or canthaxanthin was higher than that of shrimp fed D1 during the stress test (P < 0·05). In conclusion, all data suggested that astaxanthin was better than canthaxanthin as the dietary carotenoid source in the commercial diet of P. monodon, and the supplement of cholesterol could positively enhance the efficiency of astaxanthin and canthaxanthin.

[Variations of fish species diversity, faunal assemblage, and abundances in Daya Bay in 1980-2007].

Based on the 2004-2005 otter trawl survey data and the 1980-2007 relevant historical records, this paper analyzed the variations of fish species composition, faunal assemblage, diversity indices, dominant species, and abundance in Daya Bay. In the 2004-2005 trawl survey, a total of 107 fish species were recorded, belonging to 50 families and 13 orders, among which, meso-demersal fish were predominant, with 48 species recorded, and followed by pelagic and demersal fishes, with 37 and 21 species, respectively. The fishes in the Bay belonged to tropical and subtropical fauna, with the dominance of warm water fishes (97 species) and warm-temperate water fishes (10 species). The diversity index was the highest in summer (3.82), followed by in winter (3.37) and autumn (3.00), and the lowest in spring (2.40). The seasonal variation of Pielou evenness index mimicked that of diversity index. In 1980-2007, the characteristics of fish community in the Bay changed obviously. The species number reduced from 157 species in the 1980s to 110 species in the 1990s and to 107 species in 2004-2005, and the dominant species shifted from the high-value fishes such as hairtail and pomfret in the 1980s to low-value fishes such as sardine fish, anchovy, and juvenile porgy. A non-linear regression model composed of inter-annual trend and seasonal cycle was used to simulate the changes of fish stock density in 1980-1999 and 1990-2007, and the results indicated that in the two periods, the fish stock density in the Bay all showed a decreasing trend, but the decrement was larger in 1990-2007 than in 1980-1999. The seasonal variation of the stock density in 1980-1999 was relatively small, with an amplitude being 0.099, while that in 1990-2007 was relatively larger, with the amplitude being 0.420, illustrating that the fish abundance in the Bay had a larger seasonal fluctuation in 1990-2007.

[Variation characteristics of macrobenthos productivity in Daya Bay of South China Sea].

Based on the 7 cruises survey data collected from 63 research stations in the Daya Bay of South China Sea in January and July 1988 and in March, May, September and December 2004, the variation characteristics of the abundance, biomass, productivity, and P/B value of macrobenthos in the two years were analyzed by using Brey's empirical formula. The results showed that in 2004, the mean productivity and P/B value of macrobenthos in study area were 10.22 g AFDM x m(-2) x a(-1) and 0.85 x a(-1), respectively, being at the medium-high level among the sea areas in China and higher than those in 1988 (7.25 g AFDM x m(-2) x a(-1) and 0.76 x a(-1), respectively), which corroborated the conclusion that the high output system of Daya Bay relied on the fast turnover to maintain its high productivity. The variation characteristics of the productivity and P/B value varied among the four main groups of macrobenthos, and the horizontal distribution of macrobenthos productivity also had a greater variation. The regional differences of the productivity and P/B value were closed related to human activities, and the areas in which the productivity varied significantly were intensively affected by human activities.