Net depth response of a depth-controllable (towed) gillnet for fish sampling

SUMMARY: Flume-tank experiments were performed to examine the depth response of a new type of depth-controlled gillnet. Variations of net depth were investigated as the warp was paid out and wound up for different changes of warp length, main sinker weights, and winch speeds. In most experiments, when the warp finished paying out, the net continued to descend and then ascended slightly to an equilibrium depth (overshoot phenomenon). The overshoot distance was nearly constant when the warp was wound up and increased linearly with increasing winch speed when the warp was paid out. An increase in winch speed reduced net settling time, which converged on a constant value for both paying out and winding up.     

Metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) by human cytochrome P450-dependent monooxygenase systems

Metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) by monooxygenase systems dependent on 12 forms of human cytochrome P450 (CYP) was examined with the recombinant yeast microsomes containing each of the human CYP. The metabolites of PCDDs were analyzed by HPLC and GC-MS. Remarkable metabolism by the multiple CYP forms was observed toward dibenzo-p-dioxin (DD) and mono-, di-, and trichloroDDs. The metabolism contained multiple reactions such as hydroxylation at an unsubstituted position, hydroxylation with migration of a chloride substituent, and hydroxylation with elimination of a chloride substituent. Although major CYPs in human liver such as CYP2C8, CYP2C9, and CYP3A4 showed no significant metabolism toward the PCDDs, CYP1A1 and CYP1A2 showed high catalytic activity toward DD and mono-, di-, and trichloroDDs. The kinetic parameters K(m)(app) and V(max) of the CYP1A1-dependent 8-hydroxylation activity of 2,3,7-trichloro-DD (2,3,7-triCDD) were estimated to be 0.30 microM and 51 (mol/min/mol of P450), respectively, suggesting that 2,3,7-triCDD was a good substrate for CYP1A1. However, none of the CYPs showed any detectable activity [<0.01 mol/min/mol of P450)] toward 2,3,7,8-tetraCDD. Substrate-induced absorption spectrum and inhibition studies indicated that CYP1A1 could bind 2,3,7,8-tetraCDD with considerably high affinity. It was strongly suggested that the long half-life (7.1 years) of 2,3,7,8-tetraCDD in humans was due to an extremely low activity of CYPs toward 2,3,7,8-tetraCDD in addition to its chemical stability.     

Trawling experiment in a circular water tank to assess the effects of towing speed,light intensity,and mesh shape on active escape of undersized fish

ABSTRACT:   To assess the effect of towing speed and light intensity on the active escape of undersized fish through diamond and square mesh panels, a trawling experiment was simulated in a circular water tank. Juveniles of Japanese dace Tribolodon hakonensis (13-cm length class) were used as experimental fish. They were forced to swim inside a closed framed net with either diamond or square mesh (65-mm mesh size) that was moved using a speed-controllable motor. A submersible infrared CCD camera was used to observe and record the behavior of fish inside the net when it passed in front of the camera. Results indicated significant effects of towing speeds and light intensities ( P  < 0.05) on the escape of fish through the diamond and square meshes. Increase in light intensity enhanced the ability of fish to escape at lower towing speeds. At higher towing speeds, few fish could escape under light conditions. A strong negative correlation was found between towing speed and the frequency of fish escape (diamond mesh R ² = 0.99, square mesh R ² = 0.96). There was no significant difference between the numbers of fish escaping through the diamond and square meshes. These results suggest that the square-mesh panel may not be effective in the trawl cod end under dark or very low light intensity at high towing speed.     

Deodorization of soybean proteins by enzymatic and physicochemical treatments

To utilize soy protein isolate (SPI) more widely, a convenient and effective method for deodorizing it is required. This paper reports a new deodorizing method using various types of solid adsorbents made of polystyrene, polymethacrylate, and zeolite, as well as charcoal. Treatment of the SPI solution with them decreased the hexanal content in the solution, whereas the content of linoleic acid was not much decreased. A brominated polystyrene adsorbent (SEPABEADS SP207) and a zeolite adsorbent (HSZ-360HUD) removed hexanal most effectively, although 30-40% of the total hexanal remained. A model experiment showed that their hexanal adsorption capacity was much higher than the hexanal content in the SPI solution and that an excess amount of hexanal added to the SPI solution was mostly removed by them. These results suggest that hexanal in the SPI solution can be classified into two types. Hexanal of type I may be free or bound weakly on the surface of proteins and is removable by the adsorbents, whereas hexanal of type II may be bound tightly inside proteins and is unremovable by the adsorbents. Despite the considerable amount of hexanal remaining in the SPI solution even in the most successful cases, the SPI solution was well deodorized as shown by the sensory test. Accordingly, type I hexanal may be closely related to the soybean odor. Removal of hexanal by the adsorbents was not much improved by alpha-chymotryptic digestion of SPI. Type II hexanal might be in similar states even in the chymotryptic digests.     

Coagulation of soy protein isolates induced by subtilisin Carlsberg

The coagulation of soy protein isolates (SPI) induced by subtilisin Carlsberg was studied. The proteins were digested to fragments of 16 kDa or less in the early stage of the reaction, followed by coagulation. The time-course of the coagulation measured by turbidity was separated into three phases. The turbidity decreased from the initial level observed at time zero to the minimum level (OD1) at time T1 (15-20 min) in the first phase. Then, it increased drastically to reach the maximum (OD2) at time T2 (60-70 min) in the second phase, which was followed by a slight decrease in the third phase. The coagulation was terminated at T2, where 30-35% of the weight of the SPI proteins was in coagula. Proteins in the coagula were degraded slowly in the prolonged incubation, and the protein content in the coagula was finally 15-20% of the weight. The time-course of the turbidity agreed well with that of the weight of the precipitates formed, indicating that the turbidity reflects the progress of the coagulation. The turbidity change (OD1 to OD2) from the start to the end of the coagulation increased proportionally to the SPI concentration (4.9-11 mg/mL), although the time (T1 to T2) needed for the coagulation was independent of the concentration. The growth of the coagula is promoted by increasing the SPI concentration and is rate-limiting in the coagulation.     

Sampling performance and operational quality of a frame trawl used to catch juvenile fish

SUMMARY: A sampling trawl with a rigid mouth; that is, the frame trawl, was designed so as to catch the large larval and juvenile fish more efficiently. The net consisted of four 13 m panels (nylon multifilament and twine diameter φ 0.75 mm, mesh size 8 mm). The frame of the net's mouth was composed of four stainless steel pipes (length 4 m, diameter φ 76 mm, thickness 5 mm). Several operations were conducted to investigate the capability of catching juveniles. A lot of Sardinops melanostictus juveniles, which are generally difficult to catch, were caught during every operation. Underwater observations proved that juveniles could not elude the capture. The frame trawl requires no special handling and is possible to operate in a rough sea.     

Effect of towing speed and net mouth size on catch efficiency in framed midwater trawls

ABSTRACT:   To investigate fish density using rigid-mouth, towed net gear, such as a framed midwater trawl (FMT), it is necessary to know the catch efficiency. The catch efficiency with an FMT is described as the rate of fish entering the net (entering rate) versus the rate of fish retention, i.e. the mesh selectivity. This study investigated the change in the catch efficiency under several towing conditions using three types of FMT of different net mouth areas (4.0, 12.3, and 16.0 m²) with the same mesh size. The catch efficiency of the FMT was evaluated by comparing catch per unit effort obtained from each towing condition. The catch efficiency of FMT varied with towing speed and net mouth area. Particularly, the effect of net mouth area on the catch efficiency was greater than that of towing speed. Additionally, under the same towing condition, the catch efficiency for large length fish was lower than that for small length fish.     

Importance of the Shatsky Rise Area in the Kuroshio Extension as an offshore nursery ground for Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus)

Recent findings suggest that recruitment of Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus) depends on survival during not only the first feeding larval stage in the Japanese coastal waters and the Kuroshio front but also during the post‐larval and juvenile stages in the Kuroshio Extension. Spatial distributions of juvenile anchovy and sardine around the Shatsky Rise area in the Kuroshio Extension region and the Kuroshio–Oyashio transition region are described, based on a field survey in the late spring using a newly developed mid‐water trawl for sampling juveniles. All stages of anchovy from post‐larvae to juveniles were obtained in the northern Shatsky Rise area. The Kuroshio Extension bifurcates west of the Shatsky Rise area and eddies are generated, leading to higher chlorophyll concentrations than in the surrounding regions in April and May. When Japanese anchovy and sardine spawn near the Kuroshio front or the coastal waters south‐east of Japan, their larvae are transported by the Kuroshio Extension and are retained in the Shatsky Rise area, which forms an important offshore nursery ground, especially during periods of high stock abundance.