...они пропускают в обе стороны...

Kordon ® Breathing Bags™ represent a new approach to the problems of shipping live fishes and other aquatic animals and aquatic plants, including over long distances or for extended time periods. The product development staff at Kordon, teamed with plastics chemical engineers, have taken a technology first developed in space/military research and refined it to produce the bags being offered today.

The Breathing Bags allow the transfer of simple and complex gas molecules through the plastic wall of the bag -- carbon dioxide and oxygen in particular, as well as other gases - providing a true "breathing" bag in place of a "barrier" bag as is used in plastic polyethylene bags. As long as there is a breathable atmosphere outside the Breathing Bag, the animals inside will not run out of oxygen.

Carbon dioxide exits the bags at 4 times the rate oxygen enters the bags, thereby constantly purging the water of toxic carbon dioxide, and allowing oxygen to replace it in the water. Kordon has shipped around the world millions of bags (termed "Sachets") of living foods (tubifex worms, brine shrimp, daphnia, glass worms, etc.) for aquarium fishes using the Breathing Bag technology, and hundreds of thousands of Breathing Bags have been used successfully to ship fishes, coral reef animals, and aquatic plants.

По-моему это развод, лажа и глупость, ибо противу всяких законов физики.
Не бывает такого, невозможно!

...попробуй такой штукой поймай... рыба будет шарахаться, а во-вторых - если начнет трепыхаться - просто вылетит из такого "сачка"...

Т.н. «дышащие» мешки для перевозки рыб, водных беспозвоночных и водных растений Kordon Breathing Bags

позволяют обойтись без кислородных балонов и уменьшить объём груза, одновременно повышая сохранность перевозимых гидробионтов.
Краткая инструкция по использованию таких пакетов:
После добавления воды и рыбы, опечатать мешок, оставив как можно меньше воздушного пространства.
За исключением тех немногих видов рыб, которые не переносят отсутствия доступа к воздушному пространству на поверхности воды.
Каждый пакет должен быть отделён от других бумажной перегородкой. Т.к. в противном случае в пакет будет поступать меньше кислорода из окружающей среды.

Я хочу такого типа — он удобнее

по крайней мере, похоже, что из него можно курить аквариумную траву!

Он из чего сделан?

A unique way to capture smaller fishes without damage or snagging their fins in a net. Especially useful for catfishes, loaches, and other spiny rays.

The Fish Catcher is made of non-toxic blow molded plastic similar to many plastic bottles. Fish Catchers are molded clear with either a slight green or blue cast. All edges are finished smooth to protect the fish. The overall length is approximately 16.5 inches and has a bowl diameter of 4 inches. The Fish Catcher is designed with round smooth sides so that the fish will not be snagged or scraped as they would be when using a typical net. Its shape allows easy capture and removal while holding the fish in the Catcher's bowl of water. Practice will help in learning this proven method of fish catching that was first done centuries ago in Europe using catchers made of blown glass. With a little experience, fish can be caught quickly and harmlessly.

While the Kordon Fish Catcher can be used alone, a rod, dipnet or a paddle (like a plastic fly swatter) can be used to herd the fish into the Catcher. With some fish this greatly simplifies the catching operation. Approach fishes slowly and gently guide them into the bowl of the Fish Catcher. Once there, raise the fish in the bowl to the surface of the water and transfer them to a holding container that has water from the same source as the fish. Because the fish are never removed from water, trauma is reduced.