Effect of stocking density on growth performance of juvenile Amur Sturgeon (Acipenser schrenckii)

Experiments were carried out with juvenile Amur sturgeon (Acipenser schrenckii Brandt) including two size classes [small sized (SS) and large sized (LS)] to study the effect of stocking density on the growth when reared in indoor tanks. In the first trial (SS), the juveniles (8.70 +/- 0.90 cm total length) were reared at five relatively high initial stocking densities (120, 240, 360, 480, and 600 individuals m(-3)), whereas in the second trial (LS), the larger-sized juveniles (17.31 +/- 2.05 cm total length) were reared at five relatively lower stocking densities (50, 100, 150, 200, and 250 individuals m(-3)). Thus, the density differences refer to numbers rather than biomass. Each experimental trial lasted for about 30 days. The results showed that under the same experimental conditions, the growth rate of the fish decreased with increasing stocking density. By contrast, the feed conversion rate increased gradually with increasing stocking density. There was no significant difference (P > 0.05) in the average survival rates of the fish in each group in both trials, except Group 5 in SSS (P < 0.05)

Global subterranean estuaries modify groundwater nutrient loading to the ocean

International audienceTerrestrial groundwater travels through subterranean estuaries before reaching the sea. Groundwater-derived nutrients drive coastal water quality, primary production, and eutrophication. We determined how dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved organic nitrogen (DON) are transformed within subterranean estuaries and estimated submarine groundwater discharge (SGD) nutrient loads compiling > 10,000 groundwater samples from 216 sites worldwide. Nutrients exhibited complex, non- conservative behavior in subterranean estuaries. Fresh groundwater DIN and DIP are usually produced, and DON is consumed during transport. Median total SGD (saline and fresh) fluxes globally were 5.4, 2.6, and 0.18 Tmol yr1 for DIN, DON, and DIP, respectively. Despite large natural variability, total SGD fluxes likely exceed global riverine nutrient export. Fresh SGD is a small source of new nutrients, but saline SGD is an important source of mostly recycled nutrients. Nutrients exported via SGD via subterranean estuaries are critical to coastal biogeochemistry and a significant nutrient source to the oceans