Gonad development and size at maturity of the male mud crab Scylla paramamosain (Forsskål, 1755) in a tropical mangrove swamp

The reproductive traits and size at sexual maturity of the male mud crab Scylla paramamosain were investigated in Pak Phanang mangrove swamps, Thailand. Samples were taken seven times from the local middlemen mud crab traders during June 2006 to January 2008. Gonad development was determined based on histological appearance that was classified into three stages: 1) Immature (Spermatogonia), 2) Maturing (Spermatocytes) and 3) Mature (Spermatids and Spermatozoa). Among the sample population, the highest 72% was under gonad development stage I, whereas mature stage III was only 12%. The size at first maturity was estimated by the external allometric growth and histological observation of gonad. The size at which 50% of individuals attain sexual maturity was estimated by the two mathematical models such as probit analysis and logistic curve. The mean size at first sexual maturity and 50% maturation of male S. paramamosain were 96 mm and 109 mm internal carapace width (ICW) which revealed that 88% individuals were immature. The present result suggested that the minimum legal size of male S. paramamosain capture should be >110 mm ICW

Coastal Marine Protected Areas in Japan and their Institutional Characteristics

A survey was conducted to create a comprehensive list of marine protected areas (MPAs) in Japan. There exist more than 1,000 fishery cooperatives in Japan, and many of them have established no-take zones for many years. Such zones are usually not reported to the government and, therefore, the complete picture of the MPAs in Japan has been largely unknown until now. Information on such local MPAs was collected through various sources, and a list of more than 1,000 MPAs was produced. Many of them take the style of self-imposed voluntary regulations. Nonetheless, it was suggested that free-riders of the conservation activities were uncommon. This is because agreements are usually made to maximize the benefit of the group of fishers and each member of the group monitors the compliance status of other members. The government has provided territorial use right for fishers, and this could have helped maintain such a selfgovernance framework

Econometric Analysis of the Factors Contributing to the Fish Price increase in Coastal Turfs in Japan: the Case of the income Pooling Fishery for Coastal Shrimp Sakuraebi (Sergia Lucens)

While right-based managements have often been encouraged as effective management tools, few studies presented an empirical analysis on the effects of those systems. This paper focuses on a special form of Territorial Use Rights Fisheries called an income pooling system, and examines the effects of the system empirically. Income pooling system is a unique Japanese fishery management system where fishermen harvest fish cooperatively, and divide the total income based on a certain rule, in many cases equal distribution. The increase of fish price through control on landing amount and improvement of quality of fish is regarded as the main effect of the system in earlier studies, so we estimated the magnitude of the impact of two factors on the price of fish with econometric method. The results show that the two factors in fact have significant effects for the price changes. Also, the effect of the improvement of quality for the price is not negligible compared to that of control on landing amount. These results suggest that to improve the income of fishermen, the policy encouraging fishermen to improve the quality of fish is effective. This study can be regarded as one of the first attempts to use economic analysis to evaluate the economic performance of fishery management system

Community-based shrimp stock enhancement for coastal socio-ecological restoration in the Philippines

The reality of declining quality of coastal areas has been evident for many developing countries, especially in Southeast Asia. In the Philippines, rural coastal zones and estuaries are now being characterized by declining wild fisheries resources and degrading environment. This paper presents, as an example, the typical rural coastal towns of New Washington and Batan in Aklan province, Philippines and showcases how the concept of shrimp stock enhancement can provide incentives to restore the environment and provide sustainable fishing livelihood in the area. The New Washington-Batan Estuary in northeast Panay Island, Philippines was a productive fishing ground that has been in a state of degenerating brackishwater fisheries and estuarine environment. Average daily catch composed of various species decreased from 24 kg in 1970s to 0.7 kg at present. Shrimp fisheries, the most important livelihood, declined in quality and quantity. The highly-priced and once very abundant tiger shrimp Penaeus monodon was replaced with smaller-sized and lower-priced species like the Metapenaeus ensis. These can be attributed to the conversion of 76% of mangroves to culture ponds in the past 50 years and more than 400% increase in fishing gears since the 1990s. The need to reduce fishing structures and rehabilitate mangroves is evident. However, these drastic changes directly affect fishers livelihood. This paper explores the prospects of P. monodon stock enhancement as positive reinforcement for the estuary s rehabilitation. Number of gears per fisher may have to be reduced but shrimp catches will be relatively high-priced. Simulations with additional tiger shrimp caught due to stock enhancement show that fishers can increase income by more than 4 times from their current PhP 34 gear-1 day-1. Campaigns on the importance of mangrove especially as shrimp habitat can encourage local communities to reforest the estuary especially in abandoned ponds. With effective management, law enforcement, and sustained support from different sectors, shrimp stock enhancement can be a positive strategy in estuarine rehabilitation and livelihood sustainability in the New Washington-Batan Estuary

Introduction for Fisheries and Aquatic Biology

Chapter I. Aquatic Environment. Ken FURUYA and Ichiro YASUDA : chapter_1.pdfChapter II. Biology and Ecology of Aqua-Shere. Toyoji KANEKO, Katsumi TSUKAMOTO, Atsushi TSUDA, Yuzuru SUZUKI and Katsufumi SATOH : chapter_2.pdfChapter III. Aquatic Resource and Production. Ichiro AOKI, Kazuo OGAWA, Taku YAMAKAWA and Tomoyoshi YOSHINAGA : chapter_3.pdfChapter IV. Chemistry of Aquatic Organism and Their Utilization. Hiroki ABE, Shugo WATABE, Yoshihiro OCHIAI, Shigeru OKADA, Naoko YOSHIKAWA, Yoshiharu KINOSHITA, Gen KANEKO and Shigeki MATSUNAGA : chapter_4.pdfChapter V. Relation between Aqua-Shere and Human Life. Hisashi KUROKURA, Hirohide MATSUSHIMA, Shingo KUROHAGI, Haruko YAMASHITA, Akinori HINO, Kazumasa IKUTA, Satoquo SEINO, Masahiko ARIJI, Ken FURUYA, Junichiro OKAMOTO and Nobuyuki YAGI : chapter_5.pdfPart of "Introduction for Fisheries and Aquatic Biology

シオミズツボワムシの胚発生過程

筆者らはシオミズツボワムシ諸株の増殖と保存に関する一連の研究を行っているが、その中で胚発生の発生段階の明確な記載の必要が生じたことから、その胚発生の経過について詳細な観察を行った。歴代培養したいわゆる長崎株の単性生殖雌卵からの孵化個体を供試材料とし、水温25℃、塩分25‰、明暗各12時間の条件下で、海産クロレラを餌料として個別飼育を行い、それらの産出した単性生殖雌卵(親個体に懸着)の胚発生過程を顕微鏡下で連続的に観察した結果、1)産出された卵の孵化までに要する時間は、約20時間で一定していた。2)胚の発生段階は、卵の外部から識別される形態的特徴にしたがって19期に分けられた。3)産出時から各期に至るまでの経過時間、ならびに各期の形態的特徴を図示・記載すると共に、顕徴鏡写真により示した。Since the euryhaline rotifer Brachionus plicatilis is widely used as a food organisim in aquaculture, a lot of information concerning the biology of this species has been accumulated, but no information is available on the developmental stages of the amictic eggs. In the present work, some observations were made on the development of the parthenogenetic or amictic eggs of B. plicatilis reared under a constant environmental conditions (temperature: 25°C, salinity: 25%, photoperiod: 12D-12L, food: Chlorella sp.). The average time for development is ca. 20h. Based on the morphological characteristics of embryos, the process of the development is classified into 19 stages, each of which is pictured, figured and described. The pattern of early cleavage in B. plicatilis is similar to the previous descriptions in other rotifers