Nariharu Yamashita

Color vision, spectral sensitivity, accommodation, and visual acuity in juvenile masu salmon Oncorhynchus masou masou

Color vision, spectral sensitivity, accommodation, and visual acuity were examined in juvenile masu salmon Oncorhynchus masou masou to obtain fundamental information about the visual system. Two types of S-potentials were recorded from 415 horizontal cells in isolated retinas from 34 cultured freshwater masu salmon (114–219 mm standard length, SL). Although horizontal cells recording S-potentials were not identified, the horizontal cells were confirmed because their responses were maintained while the stimulus remained. The variety of chromaticity (C)-type S-potentials indicated well-developed color vision. The analysis of the luminosity (L)-type S-potentials response to ultraviolet light. The direction and extent of lens movement induced by electrical stimulation was measured in 12 cultured masu salmon (99.0–142.5 mm SL). The results indicated that the visual axis was upward and forward, and that the range of accommodation was from 0.79×SL in front of the eye to infinity. In histological analysis of the retinas of five wild smolts (100–118 mm SL), the maximum cone densities (276–345 cones/0.01 mm2) were detected in the ventral to temporal regions. The visual acuities assessed by histological methods were 0.069–0.075.

Drilling position of the ear affects growth and mortality of scallop (Patinopecten yessoensis, Jay) in ear-hanging culture

We evaluated the effect of where the hole is drilled in the shell when using the ear-hanging or Nimai-ake method in scallop aquaculture. We examined its influence on growth and mortality during 8-month growth trials on the scallop Patinopecten yessoensis at Shikabe, Japan. Our observations showed: (1) no differences in growth and mortality between drilling the hole in the posterior compared to the anterior ear; (2) that drilling at positions next to the ligament causes increased mortality; (3) that the lowest increase in shell height and total weight is obtained when the hole is drilled next to the ligament on the anterior ear; and (4) that growth is greatest when the hole is drilled near the corners of the ears (either on the anterior or posterior ears).

Estimation of the Loading and the Center of Gravity Height Using the Physical Properties of Laminaria japonica.

The estimation of the loading and the center of gravity height on a small working vessel was perfomed using the physical properties of kelp (Laminaria japonica ARESCHOUG). According to the results of the relative sensitivity analysis for each parameter, the loading and the center of gravity height can be described by the local height and area of a cargo by using the physical properties of kelp parametrically. To determine the loading at a kelp cultivating site, the initial bulk density of kelp and the area and maximum height of the cargo have to be considered. To estimate the center of gravity height, the maximum height of the cargo has to be considered.

The Relationship between the Compressive Stress and the Bulk Density of Laminaria japonica.

Simple field measurements of the physical properties of kelp (Laminaria japonica ARESCHOUG) have revealed the relationship between its bulk density and compressive stress, and this knowledge can then be used to determine the maximum load and the location of the center of gravity on a small vessel for kelp cultivation. According to the results, the relaxation and pressure gradient to the bulk density can be separated by measurement 2 minutes after loading. This moment defines the setting time as the variation in the bulk density comes within 1%, according to the hysteresis acting reciprocally on the load. The compressibility factor shows a steady value (0.464) regardless of the sampling area, against the initial bulk density which shows a wide distribution. Therefore, it may well be that this parameter consists of one of the characteristic physical properties of kelp.

Studies on the mechanization of longline gear-IV. Positioning control of a bating machine using a digital servo controller.

This paper introduces a servo mechanism as a baiting machine controller. It is designed for improving performance during high speed shooting. This controller is intended to have quick and accurate responses with regard to position reference, as well as having small speed fluctuations resulting from torque disturbance. For the control algorithm, feedback and feedforward control is applied. The feedback control law consists of proportional plus integral feedback. In order to suppress speed fluctuations, feedforward control is introduced based on observer theory which estimates torque disturbance. This disturbance is mainly due to the cutting of bait. In this paper, we have examined two kinds of servo systems, one is the proportional plus integral feedback (PI) system, and the other adds this feedback to the feedforward (PI+FF) system. The baiting machine control system is realized by a micro-computer. Numerical and experimental results of the two systems indicate that the PI+FF control system exhibits smaller speed fluctuations and faster setting times than those obtained with PI control system alone.