We investigated whether the feeding preferences of flatfish （Paralichthys olivaceus）, which is reported to have a high color discrimination ability, depended more on the feed color or the contrast between the background and target feed colors, or whether other factors were involved. We evaluated the feeding preference by using various colored lures against different background colors. The results revealed that the flatfish were most likely to feed on black lures regardless of the background color; the black lures had the highest contrast ratio against any background color other than black. The feeding preference was especially low for transparent lures and those with the same color as the background. Although it is highly likely that the flatfish selected and fed on the lures with a high contrast ratio against the background, they did not necessarily do so as they rather preferred feed of specific colors. The feeding preference for transparent, yellow, and white lures was low regardless of the background color. This finding suggests that flatfish may have a behavioral norm that causes them to consider bright-colored objects as dangers.

for each condition, with Iop, ₂ ＜ 1 indicating excessive secondary nucleation and Iop, ₂ ＞ 1 indicating excessive agglomeration. These results indicated that the parameters for growth and secondary nucleation were effectively estimated when Iop, ₂ is ＜1, and the agglomeration parameters were best estimated when Iop, ₂ is ＞1. PBM analyses across all conditions resulted in an overall error of 11 ％. Notably, smaller errors were observed when Iop, ₂ is >1 (agglomeration-dominant condition）, characterized by unimodal particle size distributions.

Malic acid was added to saltwater to evaluate the taste enhancement effects of the interaction between salt and organic acids. At salt concentrations of 0.234 ％ and 0.584 ％, the taste enhancement effects of adding malic acid were observed at the recognition threshold. However, at salt concentrations of 0.8 ％ and 1.5 ％, no taste enhancement effect of adding malic acid was observed at the recognition threshold. The taste enhancement effect was eventually observed when 0.002 ％ and 0.003 ％ malic acid were added to 0.8 ％ and 1.5 ％ saltwater, respectively. At these concentrations, a slight sour taste was noted when placed in the mouth. A strong salty taste was perceived as the dominant taste. The taste was recognized more strongly after adding more malic acid. A strongly sour taste was perceived as unpleasant, underscoring the importance of taste balance.