Soft Flesh in Sablefish, Anoplopoma fimbria, of Southeastern Alaska: Relationships with Depth, Season, and Biochemistry

The condition of soft-textured flesh in commercially harvested sablefish, Anoplopoma fimbria, from southeastern Alaska was investigated by National Marine Fisheries Service (NMFS) scientists from the Alaska Fisheries Science Center’s Auke Bay Laboratories (ABL) in Alaska and the Northwest Fisheries Science Center in Seattle, Wash. Sablefish were sampled by longline, pot, and trawl at five sites around Chichagof Island at depths of 259–988 m in the summer of 1985 and at depths of 259–913 m in the winter of 1986. At the time of capture and data collection, sablefish were categorized as being “firm” or “soft” by visual and tactile examination, individually weighed, measured for length, and sexed. Subsamples of the fish were analyzed and linear regressions and analyses of variance were performed on both the summer (n = 242) and winter (n = 439) data for combinations of chemical and physical analyses, depth of capture, weight vs. length, flesh condition, gonad condition, and sex. We successfully identified and selected sablefish with firm- and soft-textured flesh by tactile and visual methods. Abundance of firm fish in catches varied by season: 67% in winter and 40% in summer. Winter catches may give a higher yield than summer catches. Abundance of firm fish catches also varied with depth. Firm fish were routinely found shallower than soft fish. The highest percentage of firm fish were found at depths less than 365 m in summer and at 365–730 m in winter, whereas soft fish were usually more abundant at depths greater than 731 m. Catches of firm fish declined with increasing depth. More than 80% of the fish caught during winter at depths between 365 and 730 m had firm flesh, but this declined to 48% at these depths in summer. Longlines and pots caught similar proportions of firm and soft fish with both gears catching more firm than soft fish. Trawls caught a higher proportion of soft fish compared to longlines and pots in winter. Chemical composition of “firm” and “soft” fish differed. On average “soft” fish had 14% less protein, 12% more lipid, and 3% less ash than firm fish. Cooked yields from sablefish with soft-textured flesh were 31% less than cooked yields from firm fish. Sablefish flesh quality (firmness) related significantly to the biochemistry of white muscle with respect to 11 variables. Summer fish of all flesh conditions averaged 6% heavier than winter fish. Regulating depth of fishing could increase the yield from catches, but the feasibility and benefits from this action will require further evaluation and study. Results of this study provide a basis for reducing the harvest of sablefish with soft flesh and may stimulate further research into the cause and effect relationship of the sablefish soft-flesh phenomenon.

Feasibility of bi-culture of mud crab (Scylla serrata) and shrimp (Penaeus monodon)

A study on the feasibility of bi-culture of mud crab (Scylla serrata) and shrimp (Penaeus monodon) in brackishwater earthen ponds (0.1 ha each) was carried out for a period of five months (March-August). Nursed shrimp juvenile (ABL:· 3.36±0.23 em and ABW: 0.26±0.04 g) and crab juvenile (ACL: 2.61±0.22 cm, ACW: 4.63±0.11 cm and ABW: 43±2.64 g) were stocked following the experimental design of shrimp 2/m2 (Treatment-1), shrimp 2/m2 and mud crab l/m2 (Treatment-2) and shrimp 2/m2 and mud crab 0.5/m2 (Treatment-3). Crabs were fed with chopped trash tilapia @ 10~5%, while shrimp were fed with Saudi-Bangla shrimp feed @ 3~5% of biomass twice daily. Significantly (p<0.05) higher specific growth rate (SGR) of shrimp and mud crab was 1.86% (g/day) in T2 and 0.83% (g/day) in T3, respectively. The survival of shrimp and mud crab also varied significantly (p<0.05) with a higher mean value of74.63% in Tl and 51.04% in T3, respectively. The production of shrimp (424.09 kg/ha) was significantly (p<0.05) higher in Tl and that of mud crab (568.80 kg/ha) in T2. Significantly (p<0.05) highest total production of 871.29 kg!ha was in T2 followed by 708.52 kg/ha in T3 and 424.09 kg/ha in Tl. The results indicate that mud crab can be cultured at a stocking rate of 1/m2 together with shrimp at 2/m2 •

Effects of stocking density on growth and survival of Mystus gulio in nursery ponds

A study on the effect of stocking density on growth and survival of nona tengra (Mystus gulio) was carried out in brackishwater earthen nursery ponds (2 decimal each) for a period of 42 days. Five-day old captive bred tengra post-larvae (ABL: 4.53±0.83 mm and ABW:3.33 mg) were stocked at four different densities of 200/m² (Treatment-1), 250/m² (Treatment-2), 350/m² (Treatment-3) and 450/m² (Treatment-4). Fries were fed twice a day with a mixture of fine rice bran, mustard oil cake and fishmeal at the ratio of 2:1:1. The specific growth rate (SGR) of larvae did not vary significantly (p>0.05) between T1 (5.096% mg/day) and T2 (5.08% mg/day), but it was found significantly (p<0.05) higher from T3 (4.98% mg/day) and T4 (4.91% mg/day), respectively. The final survival rates of 89.25±5.41% in T1 and 88.72±6.09% in T2 were found similar (p>0.05), but significantly higher (p<0.05) than those of, 76.20±4.77% in T3 and 70.34±5.71% in T4. The results indicate that 5-day old hatchery bred nona tengra post-larvae can be nursed in earthen pond at a stocking density of 200-250/m².