Jan 13 2014

Hammerhead shark (Introduction – biology – threats) – Video

Source:www.fishconsult.org

Video credit: Hani Elmalky (USA)  – Review: Abdel Rahman El Gamal

This video was taken in the Monterey Bay Aquarium during June 2012 showing the hammerhead shark cruising amongst a large population of Pacific sardines and other fish species.  The review focuses on the leading species in this exhibition which is the hammerhead shark.

Introduction: The hammerhead sharks belong to the genus Sphyrna in the family Sphyrnidae. The small and medium size species are known to form schools of more than 100 during the day while they become solitary in the evening. The average life span in the wild is 20 to 30 years and depending on the species, their size can reach up to 6 m in length and about 450 kg in weight. Because the liver of a Hammerhead shark is rich with oil which has a lower density than water, the fish tend to float in the water rather than swim.

Hammerheads are found worldwide in warm tropical and subtropical waters along coastlines and continental shelves. Most hammerhead species are considered harmless to humans.

Description: The shape of the head is a distinct feature of hammerhead sharks. Their name is based on the lateral projections on both sides of their heads giving them a hammer-like shape. The shape of the head helps them make sharper turns without losing stability than other sharks.

The eyes being located on the sides of the shark’s distinctive hammer would allow better stereoscopic (360-degree) vision. Also, the broad sharp of the head provides a larger sensor area which would enable the shark’s sensing organs, to scan the ocean and detect the electrical fields created by prey animals even if buried under the sand in the sea bottom.

Reproduction behavior: The hammerheads reproduce once a year. They exhibit a viviparous mode of reproduction with females giving birth to live young. The fertilization is internal in which the male transfers its sperm inside the female’s body and so the embryos are nourished from their mother through a yolk sac placenta until baby sharks about 12-15 baby sharks are born after a gestation period of 10-12 months. Newly born sharks develop on their own with no parental care of any sort.

Feeding behavior: Hammerhead sharks are carnivores and are known to eat a large range of items including fish, squid, octopus, crustaceans, and other hammerhead sharks. The hammerhead shark uses its unique head to pin down stingrays; their favorite prey.

Hammerheads are characterized by the slow pass of their food through the intestines as reflected in their low feed frequency which explains their slow growth rate.

Threats: Commercial fisheries catch hammerheads is done for their fins (for fin soup), oil (for vitamin), meat, skin (for leather), and offal (for fish meal). Also, hammerheads are caught accidentally by longlining crews fishing for swordfish and tuna. The schooling pattern of hammerheads make them easy target for fishermen.  

References: National Geographic, Fast facts, Aquatic Community, Wikipedia

 

 

Permanent link to this article: https://fishconsult.org/?p=10250

Jan 13 2014

Common fish culture system in Benin

Credit: Ismael Radwan (Egypt)

The photo shows a typical fish pond in Benin whereas  such dug ponds of 200-300 m2 are filled by seepage while pumping is used to drain the pond. Usually the farm size ranges from 2-3 acres. The overall productivity usually does not exceed 2 tons/hectar of tilapia whether in monoculture system or in polyculture with African catfish.

 Benin- common fish farming system

 

Permanent link to this article: https://fishconsult.org/?p=10246

Jan 13 2014

Locally manufacturing of fish feed in Benin

Credit: Ismael Radwan (Egypt)

The advanced feed manufacturing practices is not available in Benin at the moment. Instead and as shown in the photo, locally available materially are mixed for the production of fish feed. Local feed ingredients include cassava, local fish meal, rice bran, wheat bran, and corn.

Benin - locally manufactoring of fish feed

 

 

Permanent link to this article: https://fishconsult.org/?p=10241

Jan 10 2014

Production of Nile tilapia and African catfish fingerlings at Richard-Toll station, Saint Louis, Senegal

Credit: Lo Oumy Seck (Senegal)

This earthen pond belongs is a hatchery which in turn belongs to Richard-Toll station (Saint Louis) in the north of Senegal.  The station produces about 100,000 of 2-g fingerlings of Nile tilapia (Oreochromis niloticus) every year. Moreover, fingerlings of African catfish, Clarias gariepinus are also produced.  While fry feeds mainly on natural food, commercial feed is secured for fish juveniles from outside sources. It is believed that the number of fingerlings produced in Senegal is sufficient to meet the requirements of fish farms at least in the present.

 Production of tilapia and catfish fingerlings in Senegal (01) Production of tilapia and catfish fingerlings in Senegal (02)

 

 

Permanent link to this article: https://fishconsult.org/?p=10234

Jan 10 2014

Cage farming of Nile tilapia, Oreochromis niloticus in Senegal

 Credit: Lo Oumy Seck (Senegal)

The photo shows a unit of cage farming in Senegal River. Cage aquaculture was first practiced at experimental level in Senegal in 1984. However, for variety of reasons, the outcomes during the early practices were not satisfactory. From the year 2000 onward, the practice witnesses some improvements as represented in cage structure as well as in the cage management. Such improvements led to higher productivity compared to earlier practices although still considered lower than expected.  Nile tilapia, Oreochromis niloticus is the species currently farmed in cages in Senegal whereas small-scale operations adopted cage culture of tilapia. It is believed that the number of operated cages is on the rise.

Cage farming in Senegal

 

 

Permanent link to this article: https://fishconsult.org/?p=10231

Jan 10 2014

Condition factor – Fulton condition factor

This 4-slide information bite addresses the background information on the condition factor that is also called Fulton condition factor. The bite introduced the environmental and biological factors which influence the K factor supported by some examples. The bite ended by an example of the K factor values for trout and salmon that correspond with different conditions of fish. The conclusion included issues to consider when developing a condition factor for a given fish species is intended.

http://fishconsult.org/wp-content/uploads/2014/01/Condition-factor.pdf

Permanent link to this article: https://fishconsult.org/?p=10222

Jan 07 2014

Stray animals on fish farms

Credit for the bubbies’ photo: Water use mission in Egypt (Hans van Zon – the Netherlands)

Credit for the nursing cat photo: friends who participated in Fish Culture Development during 2009

Bubbies on fish farm Kitten on a fish farm

In open fish farms, some wild animals may visit and/or stay on the farm especially when the farm provides favorable and safe stay including sheltering and food. Common wild animals of concern are dogs and cats. The photos show how bubbies and kittens are staying peacefully on fish farming facilities.

While wild dogs could serve in guarding, there are some concerns about possible transmitted diseases especially rabies.  Based on field observations, it may be of interest to know that, scaring the stray dogs to leave the farm premises was temporarily possible while the matter seems more difficult with the dogs that were born on the farm as if they stick to their place of birth with no other home.

 

 

Permanent link to this article: https://fishconsult.org/?p=10216

Jan 06 2014

Historic information: Ship ballasting from the past till now

During 1800s and before, rock ballasting was used to maintain the balance of wooden ships. During those old days, there were ballasting and de-ballasting stations in which rocks were loaded or downloaded respectively (a ballast hill is shown in the image).

After the introduction of steel hulled vessels, water has been used instead of rocks as ballast to stabilize vessels at sea. This major shift in ship ballasting has been found easier and more efficient. However, the practice showed ballast water acted as a biological belt moving variety of living organisms from the filling station and discharge it into the host environment.

Some case studies caused serious ecological and economic damage to aquatic ecosystems especially when natural enemies to the invaded organisms do not exist. Examples of the ecological damage caused by nuisance ballast organisms include the introduction of Asian algae, Odontella (Biddulphia sinensis) in the North Sea in 1903 and the zebra mussel in Lake St. Clair in 1988 before spreading into the Great Lakes. The introduction of cholera, Vibrio cholerae, into Peru via ballast water in 1991 and associated human risks is another example.

The global recognition of the threats associated with the ship’s ballast water has necessitated the developing of guidelines and management strategies for ships’ ballast at national or global levels.

Ship ballasting (ballasting hill)

 

 

Permanent link to this article: https://fishconsult.org/?p=10212

Jan 05 2014

Self-cleaning tanks in fish culture

The use of round tanks in aquaculture is favored especially in intensive farming systems whether in hatcheries or grow-out operations. The preference of these tanks is based on the features of these tanks including its naturally self-cleaning action.

When water enters any of these tanks, water swirls around the tank and because of the bottom slope towards the center, the solid loadings (feces and uneaten feed) are swept to the central outlet, where they are flushed out in the discharged water.

While round self-cleaning tanks are often made of fiberglass –especially for smaller sizes- as shown in the photo, it could be constructed of other materials such as steel or concrete.

In addition to the self-cleaning features, these tanks are essential for active swimming fish species and also offer a better mixing of water and secure more efficient oxygenation.

Self cleaning tank

 

 

Permanent link to this article: https://fishconsult.org/?p=10207

Jan 04 2014

Zooplankton analysis in fish pond water – Video

The video is a part of a training program demonstrating the analysis of zooplankton in a fish pond. As shown in the video, a plankton net is used in the sampling procedures. The mesh size of the net determines the size range of the plankton trapped. A-80μm net will retain small zooplankton such as rotifers whilst allowing most algae and protozoa to pass through. Depending on the target zooplankton, the mesh size of the plankton net may range from as small as 80μm to as large as 300 and 500 µm. Similarly, the quantity of sampled water which is poured in the plankton net is related to the fertility level of pond water; while 40-50 liter may could be required in low-fertile pond, ten liters will be sufficient in case of high fertile waters. If quantitative sampling is desired, the volume of sampled water should be recorded to relate the number of organisms to a unit of water. This conical plankton net is made from nylon ending by a sample bucket. Typically, the net is held halfway out of the water, sampled water is poured through the net while assuring that all zooplankton is collected in the bucket before its preserving and analysis. After each use, the net is thoroughly washed with water and stored in the dark.

 

 

Permanent link to this article: https://fishconsult.org/?p=10202

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