Benjamin Daly

Total Lipids, Lipid Classes, and Fatty Acids of Newly Settled Red King Crab (Paralithodes camtschaticus): Comparison of hatchery-cultured and wild crabs

ABSTRACT Little is known about the nutrition or lipid metabolism of cold-water crabs, particularly in the North Pacific. We undertook a 2-part study to understand more completely the energetics and nutritional requirements of juvenile red king crab (RKC; Paralithodes camtschaticus). First, we investigated changes in proximate composition, total lipids (TLs), lipid classes, and fatty acids (FAs) throughout a molt cycle (C4–C5). Trends in lipid parameters were described by a 3-part piecewise linear regression with 3 distinct stages: (1) a postmolt phase (∼0–7 days), (2) an intramolt stage (∼7–24 days), and (3) a premolt stage (∼24–33 days). Significant intramolt differences in TLs indicated that caution should be taken when comparing crabs of unknown molt stage in future aquaculture and ecological experiments. However, little variability was found in the proportional FA composition of crabs, indicating that the intramolt stage has little effect on the interpretation of FA biomarkers. During a second investigation, we examined differences in lipid classes and FAs from cultured and wild RKC. We found significantly higher proportions of the essential fatty acids (EFAs) 20:5n-3 (EPA) and 20:4n-6 (AA) in wild crabs compared with cultured animals at the same stage. Furthermore, higher proportions of bacterial markers and lower proportions of Zooplankton FA markers were found in wild than in hatchery-reared crabs. Here, we provide the first baseline data for future dietary studies on juvenile cold-water crabs. We suggest that an initial EFA ratio for DHA:EPA:AA of 5:8:1 could be used as a starting point for controlled dietary studies on the effect of EFAs on juvenile growth, molt success, and survival.

Morphometrics, Fecundity, and Hatch Timing of Blue King Crabs (Paralithodes Platypus) from the Bering Strait, Alaska, USA

Abstract The Bering Strait marks the northern species boundary for blue king crabs (Paralithodes platypus), but the life history of the population at this latitude has never been described in scientific literature. Blue king crabs were collected in shallow (10-23 m) waters near King Island (n: males  =  199; females  =  260) in July of 2005 and from near Little Diomede Island (n: males  =  40; females  =  19) in April of 2007 for morphometric, fecundity and hatch timing information. Crabs from Little Diomede and King Islands showed no significant difference in male carapace length (CL) by location and were smaller than blue king crabs from more southern parts of the state (mean CL ± SE: 108.45 ± 0.70 mm). Females from King Island (mean CL ± SE: 99.47 ± 0.52 mm) were significantly larger than female crabs collected from Little Diomede Island (mean CL ± SE: 93.11 ± 2.96 mm) and male crabs (mean CL ± SE: King  =  107.98 ± 0.73; Diomede  =  110.13 ± 2.24) were significantly larger than female crabs at both locations. Weight of female crabs (mean ± SE: 810.0 ± 61.9 g) increased with CL according to a non-linear function; Crab weight  =  0.00165*(CL)2.8995 (r2  =  0.86). Fecundity estimates based egg counts (mean ± SE: 62,955.6 ± 4981.2) were slightly higher than visual estimates of hatched larvae (mean ± SE: 56,570 ± 6690). Timing of larval release differed significantly between female crabs held in the laboratory for 1 and 13 months. Crabs held for 1 month began hatching in mid-May 2008 with more larvae released per day and over a shorter duration (12 d). Crabs held for 13 month released fewer larvae per day over a longer duration (20 d) starting in mid-February 2009. Long-term laboratory holding may impact hatch timing due to differences in ambient temperature and perhaps other suppressed seasonal effects of the artificial environment.