Effects of diet, stocking density, and substrate on survival and growth of hatchery-cultured red king crab (Paralithodes camtschaticus) juveniles in Alaska, USA

Juvenile red king crab (Paralithodes camtschaticus) mass rearing was conducted in Seward, Alaska, USA in a king crab stock enhancement feasibility study. Hatchery-raised juveniles were cultured from larvae of 12 ovigerous females collected from Bristol Bay, Alaska, USA. Juvenile instars were cultured in nursery grow-out containers in two phases: (1) C1–C3 juveniles and (2) C3–C6 juveniles. Experiments lasted for 42 and 44 days, respectively, and tested the suitability of various diets, stocking densities and substrates in terms of survival rate and growth. The first experiment (C1–C3) compared fully-factorial treatments of three diets (Cyclop-eeze®, enriched Artemia nauplii, or Zeigler™ shrimp feed), three stocking densities (500 m− 2, 1000 m− 2, or 2000 m− 2), and two substrates (none or a combination of artificial seaweed, gillnet, and mechanical biofilter medium). The second experiment (C3–C6) used a mixed diet and compared fully-factorial treatments of two stocking densities of 800 m− 2 and 1600 m− 2 and two substrates (as above). No one food produced the highest survival and growth to C3. Cyclop-eeze® yielded highest survival (62.7%) with low growth (wet weight 8.63 mg and CW 2.04 mm). Crabs on shrimp nursery feed had the highest wet weight (10.0 mg) and CW (2.14 mm) but with low survival (44.5%). The highest stocking density resulted in a decrease in survival in both experiments. Lower stocking densities of 500 m− 2 and 800 m− 2 had relatively high survival of 58.7% and 48.7%, respectively, while the 1600 m− 2 and 2000 m− 2 densities had survival of 30.5% and 44.7%, respectively. Growth appeared to be inhibited at the highest density (2000 m− 2) in the C1 to C3 stages, as crabs at this density were smaller and weighed less than at the 500 m− 2 or 1000 m− 2 density. Complex artificial substrate increased survival and reduced growth in both experiments, likely due to reduced cannibalism and increased time spent foraging. Among substrate treatments, highest abundances of crabs were observed on artificial seaweed, which may more closely resemble preferred natural substrate. These results suggest that culturing red king crab juveniles at low to intermediate stocking densities with a mixed diet in the presence of artificial substrate provides good survival. Intermediate densities may provide for greater production without great loss in survival.