Japanese flounder

Japanese flounder image from http://www.lib.noaa.govFollowing on from information about the Southern Flounder; the culture of flounder in Japan and Korea is well documented.

Tetsuo Fujii and Masayuki Noguchi, from the Japan Sea National Fisheries Research Institute, have published a report entitled Interactions Between Released and Wild Japanese Flounder (Paralichthys olivaceus) on a Nursery Ground. The abstract:

The Japanese flounder, Paralichthys olivaceus, is one of the most important fishes in the coastal fisheries of Japan. But recently, overfishing has caused a reduction of the stock size. To enhance the stock, artificial seeds of Japanese flounder have been released. Interactions between released and wild flounder were examined to determine the success of the stocking program.

We performed experimental releases of artificial seeds in the shallow waters off Igarashi-Hama on the northwestern coast of Japan, from 1990 to 1992. The growth rate of wild flounder varied annually depending on the abundance of mysids that are the most important food for the flounder on the nursery ground. When mysids were less abundant, released flounder dispersed rapidly from the release site, ingested small amounts of food, and grew slowly compared with other years.

The feeding habits of released flounder differed from those of wild flounder when mysids were less abundant. Flounder released then ingested less food and also consumed gammarids which the wild flounder never ate. It was assumed that an abundance of mysids was more critical for released than for wild flounder. Further investigations on the carrying capacity of the nursery ground and improvement of the quality of artificial seeds are needed to enhance the stock size of Japanese flounder efficiently.

Nozomi Okada, Masaru Tanaka, and Masatomo Tagawa from the Division of Applied Biosciences, Graduate School of Agriculture,
Kyoto University, have published research entitled Bone development during metamorphosis of the Japanese flounder (Paralichthys olivaceus): differential responses to thyroid hormone. From the abstract:

The larvae of flatfish change their body structure during metamorphosis, including dramatic translocation of one of the eyes from one side of the body to the other. Such metamorphic processes are in general promoted by thyroid hormones (THs). This study focuses on the response of individual tissues to hormones, and morphological characteristics were examined in hormone-deficient larvae of the Japanese flounder (Paralichthys olivaceus).

Osamu Tominaga et al have published research entitled Daily Ration of Hatchery-Reared Japanese Flounder Paralichthys olivaceus as an Indicator of Release Place, Time and Fry Quality. In situ Direct Estimation and Possibility of New Methods by Stable Isotope. From the document:

Japanese flounder Paralichthys olivaceus is one of the most important target species of stock enhancement in Japan. The release size of hatchery-reared flounder is an important factor affecting survival after release. In order to improve the stocking effect of hatchery-reared juveniles, it is necessary to determine the optimum release place and time. Food availability for stocked juveniles is a key factor to evaluate the quality of release tactics. However, it is not easy to estimate the biomass of food organisms in the release area, because of the difficulty in quantitative sampling. Feeding intensity of released juveniles is affected by not only healthy condition of fish (vitality and nutritional status), but also physical, biological, and environmental conditions in the release area. Therefore, daily ration of fish after release becomes the useful tool to evaluate the release place, time and fry quality.

Aqua magazine (Chile) report some $45 million had been invested developing flounder farming in Chile using Japanese technology. The Japanese flounder had been introduced to Chile in 1997 via Hawaii.

Flounder offer some other interesting aspects from an aquaculture perspective. According to a summary of flounder information from the National Oceanic and Atmospheric Administration of the USA,

Flounder are naturally docile and not easily agitated. As a result, they subject themselves to little stress under farming conditions and, therefore, do better than more excitable species. They also like crowding together, though, as flatfish, they do not fully use the water column as do round fish such as large yellow croakers. In fact, stocking densities for flounder are usually expressed in terms of kilograms per square metre, rather than kilograms per cubic metre as they are for round fish. Optimum stocking density for flounder varies from 20 to 30 kg per square meter. This does not appear to stress them and, in this respect, they are similar to other farmed flatfish such as the European turbot and Atlantic halibut.

Flounders accept dry formulated feeds well and convert them efficiently, the feed conversion ratio (the weight of distributed feed per unit weight gain) being equal to 1:1 or a little more. This might be due to an intrinsic virtue of flounder metabolism and/or to a sedentary life style. If such excellent feeding efficiency could be achieved in large scale commercial systems, it would provide flounder farmers with a significant advantage from the economic point of view.

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