Microalgae is one of the most important components in the aquatic ecosystem, and they are increasingly used in food and medicine production for human consumption due to their rapid growth cycle and survival ability in the harsh environment. Now, the exploration of microalgae has been gradually deepening, mainly focused on the field of nutrition, medicine, and cosmetics. A great deal of studies has shown that microalgae have a variety of functions in regulating the body health and preventing disease, such as nitrogen fixation, antitumor, antivirus, antioxidation, anti‐inflammatory, and antithrombotic. Furthermore, microalgae can synthesize various high‐valued bioactive substances, such as proteins, lipids, polysaccharides, and pigments. In this paper, we have briefly reviewed the research progress of main bioactive components in microalgae, proteins, lipids, polysaccharides, pigments, and other nutrients included, as well as their present application situation. This paper can provide the guidance for research and development of industrial production of microalgae.

Carangidae are ecologically and economically important marine fish. The complete mitogenomes of three Carangidae species (Alectis indicus, Decapterus tabl, and Alepes djedaba) were sequenced, characterized, and compared with 29 other species of the family Carangidae in this study. The length of the three mitogenomes ranged from 16,530 to 16,610 bp, and the structures included 2 rRNA genes (12S rRNA and 16S rRNA), 1 control region (a non-coding region), 13 protein-coding genes, and 22 tRNA genes. Among the 22 tRNA genes, only tRNA-Ser (GCT) was not folded into a typical cloverleaf secondary structure and had no recognizable DHU stem. The full-length sequences and protein-coding genes (PCGs) of the mitogenomes of the three species all had obvious AT biases. The majority of the AT-skew and GC-skew values of the PCGs among the three species were negative, demonstrating bases T and C were more plentiful than A and G. Analyses of Ka/Ks and overall p-genetic distance demonstrated that ATP8 showed the highest evolutionary rate and COXI/COXII were the most conserved genes in the three species. The phylogenetic tree based on PCGs sequences of mitogenomes using maximum likelihood and Bayesian inference analyses showed that three clades were divided corresponding to the subfamilies Caranginae, Naucratinae, and Trachinotinae. The monophyly of each superfamily was generally well supported. The divergence time analyses showed that Carangidae evolved during three geological periods, the Cretaceous, Paleogene, and Neogene. A. indicus began to differentiate from other species about 27.20 million years ago (Mya) in the early Miocene, while D. tabl (21.25 Mya) and A. djedaba (14.67 Mya) differentiated in the middle Oligocene.

Using bottom-trawl survey data to examine fishery resources in the Beibu Gulf, South China Sea, changes in stock density, dominant species composition, mean trophic level, and the fishing-in-balance index were comprehensively analyzed. The results show that the stock density of fishery resources declined in the gulf from 1961 to 2017. The composition of dominant species in trawl surveys from Beibu Gulf changed greatly from 1961–1962 to 2016–2017 and showed a shift from bottom species to pelagic species and from high-trophic-level species to low-trophic-level species. Catches of low-trophic-level species increased, while the dominance of high-trophic-level species declined. The mean trophic level of fish from the gulf declined from 3.90 in 1961–1962 to 3.45 in 1998–1999 at a rate of 0.13 of a trophic level per decade and then began to increase to 3.65 in 2016–2017 at a rate of 0.12 of a trophic level per decade. The fishing-in-balance index dropped to –0.96 in 1998–1999 and then slightly increased. The results indicate that fisheries resources in the Beibu Gulf have been overfished. Therefore, we recommend reducing fishing pressure and strengthening the implementation of protection measures, such as summer fishing moratoriums, enhancement, and artificial reef construction.