Larval Fish Assemblages and Distribution Patterns in the Zhongsha Atoll (Macclesfield Bank, South China Sea)

The remote coral reef in the deep sea is one of the most important nursery grounds for many marine fishes in the South China Sea. Diversity studies on larval fishes in this area are few, and the fish information on the coral reefs ecosystem is lacking. In this study, larval fishes were sampled during the summer of 2019 from the Zhongsha Atoll in the South China Sea and identified using DNA barcodes for the first time. Ninety-five larval fish species were recognized, belonging to 37 families and 12 orders based on morphological classification and DNA barcoding identification. The larval fish collected could be assigned to three categories as reef-associated, deep-sea, and pelagic. Most of the species were small fish with low commercial value but would play an essential role in the coral reef ecosystem. Some commercial fishes, including Auxis thazard, Euthynnus affinis, Sarda orientalis, Decapterus macarellus, Lutjanus viridis, and Centropyge vrolikii, were the dominant species higher than 2% total catch. The larval fish assemblage showed distinct spatial differences responding well with the geographical conditions. The most reef-associated fish occurred inside the Atoll, and the abyssal fish presented near the edge. In addition, larval fish spread over from the southwest to northeast may reflect the oceanography effect.

Seasonal and Spatial Distribution Patterns of Ichthyoplankton Along the West Coast of Sri Lanka

Fundamental understanding of fish resources has become a crucial need in Sri Lanka for the sustainable management of fish stocks. Knowledge of ichthyoplankton essential in identifying the spawning dynamics of fish is scarce in this region of the Indian Ocean. A survey was conducted in 2018 covering different monsoon seasons to monitor the abundance, distribution, and diversity of ichthyoplankton along the west coast of Sri Lanka. Samples collected using vertical and horizontal WP2 hauls showed a total of 4095 fish eggs, with identification possible only to 3 families: Clupeidae, Engraulidae, and Cynoglossidae and 465 larval fish belonging to 23 families. The most dominant families recorded were the Siganidae, Blenniidae, Clupeidae, Gobiidae, and Engraulidae, which highlight the importance of pelagic and demersal fish along the west coast. A significant temporal pattern in egg abundance was observed with the highest abundance in March (535 10 m-3) in vertical WP2 net hauls. Furthermore, significant differences in spatial patterns of larval abundance were seen in vertical and horizontal samples. High larval fish abundances were recorded in March and during September - November, with northern regions generally having the highest abundances (~36 larvae 10 m-3). The spawning coincides with the productive southwest monsoon period (May to September). The high diversity and abundance of eggs and larvae recorded in this study indicate that the west coast is likely an important spawning and nursery ground for demersal and pelagic fish.

Ichthyoplankton Species Composition and Assemblages From the Estuary to the Hukou Section of the Changjiang River

Estuary river–lake (ERL) complex is critical for the development of ichthyoplankton, which plays an essential role in the breeding, nursing, and recruitment of freshwater fish species. In this study, different ERL sections were selected to investigate the ichthyoplankton assemblage from the Changjiang River estuary to its Hukou section between May 2018 and August 2020. During the study period, fish larvae of 40, 35, 54, and 46 fish species were sampled in the Rugao (RG), Nanjing (NJ) (nearby estuary), Anqing (AQ), and Hukou (HK) (connected river–lake) sections in the Changjiang River, respectively. Results on ichthyoplankton surveys revealed fluctuating assemblage patterns in the different river sections; larval fish species composition presented ecological habitat-dependent characteristics, which supported the importance of ERL complex for ichthyoplankton development. Furthermore, the density of fish larvae was negatively correlated with water transparency but positively correlated with water temperature, the daily rate of water level increase, and runoff in the limitative range. A generalized additive model analysis indicated that the hydrological factors significantly affecting larval fish abundance are water temperature, transparency, the daily rate of water level increase, and runoff (p < 0.05). These results also indicated that river estuaries and river–lake connected complexes are essential for ichthyoplankton recruitment and migration. In combination with the historical record, ichthyoplankton assemblage’s patterns in the Changjiang River lower reaches were preliminarily elucidated, although additional works are needed such as assessing effects on their survival and recruitment.

Assemblage Structure of Larval Fishes in Epipelagic and Mesopelagic Waters of the Northern Gulf of Mexico

The early life stages of fishes play a critical role in pelagic food webs and oceanic carbon cycling, yet little is known about the taxonomic composition and distribution of larval fishes in the northern Gulf of Mexico (GOM) below the epipelagic (<200 m). Here, we provide the first large-scale characterization of larval fish assemblages in the GOM across epipelagic, mesopelagic, and bathypelagic regions (0–1,500 m), using samples collected during the Natural Resource Damage Assessment conducted following the Deepwater Horizon oil spill (DWHOS). These data contain > 130,000 ichthyoplankton specimens from depth-discrete plankton samples collected across 48 stations in the GOM during six cruises conducted in 2010 and 2011. We examined indices of abundance and diversity, and used a multivariate regression tree approach to model the relationship between larval fish assemblages and environmental conditions. The total abundance of larval fish followed a generally decreasing trend with increasing depth, and family-level richness and diversity were significantly higher in the epipelagic than mesopelagic and bathypelagic regions. Fourteen distinct assemblage groups were identified within the epipelagic, with depth, surface salinity, and season contributing to the major branches separating groups. Within the mesopelagic, seven distinct assemblage groups were identified and were largely explained by variation in depth, season, and surface temperature. Bathypelagic assemblages were poorly described by environmental conditions. The most common epipelagic assemblage groups were widely distributed across the GOM, as were all mesopelagic assemblage groups, suggesting limited horizontal structuring of GOM larval fishes. Of the mesopelagic-associated fish taxa, four dominant families (Myctophidae, Gonostomatidae, Sternoptychidae, Phosichthyidae) comprised the majority of the catch in both the epipelagic (63%) and combined mesopelagic and bathypelagic (97%) regions. Dufrêne-Legendre indicator analysis confirmed that these dominant families were characteristic of epipelagic and mesopelagic assemblages; the larvae of less common mesopelagic-associated families largely identified with epipelagic assemblage groups. A lack of baseline data about the distribution patterns of early life stages of mesopelagic fishes in the GOM was apparent following the DWHOS, and these findings provide a valuable reference point in the face of future ecosystem stressors.

Species identification of larval fish in Hawaiian waters using DNA barcoding

Background: Correct identification of fish larvae is notably difficult, given that the morphological features at this stage of development are often poorly defined. However, obtaining such taxonomic information is of considerable importance from the perspectives of fisheries management and conservation. Results: In this study, we collected a total of 95 specimens of larval fish from Hawaiian waters, which we sought to identify using DNA barcoding based on mitochondrial DNA cytochrome oxidase subunit I sequences. Among these, 40 and 52 samples were accordingly identified to the species and genus levels, respectively. The determined average Kimura-2-parameter distances within species, genera, families, and orders were 0.72%, 25.99%, 26.30%, and 27.50%, respectively, and the mean interspecific distance was found to be 36-fold higher than the mean intraspecific distance. Conclusions: The results of this study provide convincing evidence that DNA barcoding can serve as an effective tool for the accurate species identification of larval fish in Hawaiian waters, and could thereby make a valuable contribution to species diversity surveys. The findings of this study can make a valuable contribution to our knowledge of the diversity and dispersal of larval fish in Hawaiian waters.

Larval Fish Community in the Northwestern Iberian Upwelling System during the Summer Period

The Galician shelf (northwestern Iberian Peninsula) is a highly dynamic area with an important multi-species fisheries industry that exploits resources from several habitats, characterized by being not only highly diverse, rich, and productive but also seasonally and interannually variable. Early life stages of different species are distributed throughout the year, with fluctuating abundances and community composition. Likewise, the influence of environmental factors and processes on larval production and survival remains unknown. Sampling was carried out in July 2012, and all the larvae obtained were identified to establish the specific composition of the community in a summer upwelling scenario. The results show no zonation in the species distribution, a consequence of the mixing effects of the upwelling and eddies, with high diversity but low abundance, which render in a slight predominance of a few species. Due to the dependence of planktonic populations on upwelling events, which was not highly pronounced in 2012, we cannot conclude that this was a typical conformation of the Galician summer larval fish community, but it is a first approach to comprehend the community composition.