aquaculture

R. J. Slack-Smith has written and the FAO published a manual entitled Fishing with Traps and Pots. It describes the basic elements of fishing with traps and pots for small-scale fishermen. It presents the various types of traps and pots and their construcion and gives guidance on how to choose the appropriate gear, how to rig it, how to use it to improve the catch, how to select places to fish, soaking time and finally care of the catch. The document is also available (as a .pdf) for download.

From Chapter 1:

Fishing is one of the oldest ways by which people have fed themselves and their families. Except for gathering shellfish by hand and spearing fish, primitive trapping is probably the oldest form of fishing.

In early times, flowing water caused by tidal movement and changes in river and lake levels were probably used to trap fish behind rudimentary barriers, often made from sticks and stones. It is likely that early humans found that fish catches could be improved by driving fish into these barriers. They would have found that catches from these barriers decreased over time, as fish became accustomed to them, and would have had to move the traps to fresh areas where more fish could be caught. It would have been hard work to construct new traps, either by moving stones from the old trap or finding new ones. Primitive fishers probably tried making barriers from lighter, more readily available material such as tree branches, brush and vines. This led to the fishers inventing lighter, movable traps made from brush and nets made from vines which they could carry with them when they moved to new areas. They may even have tried bigger, more complicated corral-type fish traps in lakes, rivers and coastal waters.

Slightly off topic, but interesting never-the-less, this article describes how to construct a very simple low-cost compound microscope. The designers claim the microscope is one that just about anyone can build and will produce a magnification of about 75 times.

From the introduction: A One Dollar Compund Microscope:

Microscopes may be thought of as very intricate and mysterious instruments but in reality, they are not as complicated as one may think. Building this simple instrument is not only a fun project, it will help you understand how microscopes work. This microscope, which will cost you no more than about a dollar or so to build, is essentially identical to the expensive microscopes that professionals use. Through this project you will gain an appreciation for the need of using corrective optics to reduce the aberrations. Obviously, the performance of this simple microscope cannot be compared with those more expensive professional instruments, which will produce much clearer and brighter images. Nonetheless, it should compare well to the low-cost microscopes that are sold in the toy or hobby shops. It is our experience that so called “toy microscopes” are a real disaster because they commonly give little more than diffuse images or shadows, and can give a young person a bad impression about microscopes consequently causing them to loose interest in these instruments. However, an instrument of suitable quality has the potential of sparking a young person’s interest and opening up a world of discovery to them.

There is a variety of information relating to electric fishing in the Annex 1 – Water Analysis – Sampling of Fish with Electricity, arising from the progress report from the FAO’s European Inland Fisheries Advisory Commission 21st Session, held in Budapest, Hungary, 1-7 June 2000.

An examination of the use of electrofishing is presented at www.fisheriesmanagement.co.uk:

Introduction
One of the key tools available to fisheries management is that of electrofishing. Electrofishing is a reasonably simple concept to explain practically, but theoretically it can be rather confusing. Simply, a field of electricity is passed through the water that causes a muscle response reaction from the fish forcing them towards the netsman. A full explanation can be found later on this page. The main purposes for electrofishing are stock assessment, sampling/health surveys, tagging, catching spawners, anaesthetising or eliminating species

Application
Electrofishing is an effective tool for fishery scientists because most aquatic organisms become motionless when the body voltage exceeds a certain value from nose to tail. Early methods were only applied to freshwater streams and small pools; this was due to limited knowledge of fish reactions.

The inherent nature of the process allows shallow water to be fished successfully; also there are limits on the total area that can be worked. Taking these two principals into consideration the ideal waters would be small shallow rivers, commonly chalk streams, drained canals or full navigational pathways with a maximum depth of 2.5 metres; the width of the canal is the main restriction. Conversely, the littoral zones of lakes and reservoirs lend their self to efficient electrofishing especially if there are many bank side features such as overhanging bushes, trees or reed beds. The aforementioned site descriptions tend to be very difficult to seine net thus electrofishing is the ideal replacement. On occasions fish traps can work well as an alternative if instant results are not required. Electrofishing can be undertaken in many forms with the most common applications being classical wading, classical boat fishing, trawling and screening/guiding.

New Zealand Qualifications Authority has offers an assessment standard entitled: Explain the principles of electric fishing and operate electric fishing equipment developed in association with the Seafood Industry Training Organisation (SITO).

Filipino Agriculture Secretary, Luis Lorenzo, announced recently that a Filipino aquaculturist had developed a technology which enables live fish to be transported, alive, for several hours, without water. This would allow fish traders to bring in more fish and earn more profit.

Lorenzo said the technique, officially introduced on June 8, extends a fish’s survival without water by virtually putting it into a deep sleep or in “suspended animation” using certain procedures and some liquid solutions, and later allowing it to recover from unconsciousness and get back to life.

Lorenzo, citing a report from Bureau of Fisheries and Aquatic Resources director Malcolm Sarmiento Jr., said the new technology is a better alternative to conventional practices of putting fish in containers with water, a cumbersome and costly method.

“Let in be known in the fishing world that the Philippines has now developed a technology for waterless transport of live fish, a method that will revolutionize the way we normally handle fish after harvest,” he said.

In recent test to determine if the technique works, groupers (lapu lapu) delivered to the BFAR central office laboratory in Quezon City from Iloilo using the “waterless technology”. The fish were observed to regain consciousness after eight hours of travel, with the temperature in the storage box at 25 degrees C, Sarmiento said.

Groupers, Epinephelus spp ~ source: SEAFDEC/AQD – Technotips

Popularly known as “lapu-lapu” in some Philippine dialects are important marine fishes belonging to the Family Serranidae. Thick-set or stout bodies, slightly elongate with brown spots or blotches, characterize them. They also have very large mouths and normally protruding lower jaw. It is, however, difficult to differentiate one species from another due to the fish’s ability to change colors.