Distribution and habitat conditions of walleye pollock Theragra chalcogramma at southern Kuril Islands

Data on spatial distribution and habitat conditions are presented for walleye pollock Theragra chalcogramma at southern Kuril Islands in spawning season (spring 2015) and feeding season (summer 2016). In spring, walleye pollock are distributed over the entire shelf and continental slope down to 900 m depth and occupy the upper layer on the shelf and intermediate layer at the slope with water temperature 0.1–1.5 o C. In summer, they aggregate at the depth of 200–270 m beyond the shelf in the intermediate water at the Pacific slope of Iturup Island, under the temperature of 1.3–2.9 o C. Both spatial and bathymetric migrations of pollock are minimal at the Pacific side of Iturup, but they migrate for spawning westward and southwestward to the Okhotsk Sea and slope of Small Kuril Ridge where concentrate at the benthic front between the tidal mixing zone and the Intermediate water. Seasonal redistribution of walleye pollock is accompanied with changes of size-age structure in the main aggregations.

Some of test results of the “Aldofix” in fixing the phytoplankton on the example of eggs of walleye pollock Theragra chalcogramma

Data about new conservant “Aldofix” to fix ichthyoplankton are demonstrated. Series of experiments on the conservation of ichthyoplankton and eggs of walleye pollock were carried out with the use of “Aldofix” and its modernized solutions. External view, including color of the eggs, as a result of fixing in different solutions was described, and difference in the egg diameter was noted in case of fixing in formalin and “Aldofix”. It is concluded, that “Aldofix” (example № 1) was the most convinient fixing solution to preserve ichthyoplankton.

Influence of the Technological Cycle «Fixing» on the Quality Characteristics of Pollock Fillets (Theragra Chalcogramma)

Pollock (Theragra chalcogramma) remains one of the main fishing objects in the far Eastern region. The most popular product on both the domestic and international markets is fillet, when it is frozen it can be used to produce a wide range of finished products. The main technology for obtaining iced fillet consists of its production in a fixed or loose form. A man conducts the operation «fixed fillet» immediately after filleting fresh fish by irrigation or immersion in a cold 10 % solution of table salt. The research purpose was to determine changes in the quality characteristics of fixed and unfixed Pollock fillets during cold storage. The research object was refrigerated fixed and unfixed fillet of Pollock stored at a temperature below minus 18 degrees for up to 26 weeks. During storage the authors run organoleptic assessment on refrigerated, defrosted fillets after the cooking test. The results are the following: after 6 weeks of storage the organoleptic quality indicators are quite stable for all types of fillets; after 14 weeks there is a 40 % decrease in the overall score for the fixed fillet; moreover, there are the main changes in the samples after cooking for the most significant organoleptic indicators: color, taste, smell, consistency. After 14 weeks of storage the quality indicators of loose fillets remained almost unchanged. By the 14th week of storage the freshness value coefficient of the fixed fillet increases almost 3 times (from 14.8 to 40.0), i.e. a man can consume the fish only after mandatory cooking. The study identified that the operation of fixing fillet preserved the fillet block integrity, giving greater mechanical strength to the fillets, reducing the tissue juice loss, but it is inferior in organoleptic parameters to the loose fillet during storage reducing its shelf life. According to the experiment results, the researchers recommend a storage period for fixed frozen fillet of Pollock – up to 5 months, for loose fillet – up to 7 months without considering packaging materials.