Apr 27 2014

Fish culture Development training course – Africa (2014)

EICA JICA 2014 (02) EICA JICA 2014 (01)These are group pictures during the first technical day of “Fish Culture Development – Africa” training course. This 3-month training course is being organized by the Egyptian International Center for Agriculture – EICA” and jointly supported by EICA and Japan International Cooperation Agency (JICA). The photos shows Dr. Abdel Rahman El Gamal and the course participants: Ignace Gohoun (Benin), Corneille Wantofio (Benin), Innocent Zambou (Cameroon), Joseph Bolaya Betomta (DR Congo), Chantal Sengue Ngoulou (Gabon), Jean Michel Megne Me Zeng (Gabon), Ivan Venkonwine Kaleo (Ghana), Patrick Appenteng (Ghana), Laban M. Silli (Malawi), Carolyn M. Chinguo (Malawi), Hermenegilde Iyakaremya (Rwanda), Khamis killei John (South Sudan), Mamoun Obeida (Sudan), Twasul Musa (Sudan), Fadhili Ruzika (Tanzania), and Majorie Mbambara (Zambia).

 

 

 

 

 

 

Permanent link to this article: https://fishconsult.org/?p=10745

Apr 24 2014

Japanese giant spider crab, Macrocheira kaempferi (introduction – habitats – biology – utilization)

Introduction

This photo of the Japanese giant spider crab (Macrocheira kaempferi) was filmed by Samart Detsathit (Thailand)  (shown in the photo) at Kamogawa Sea World, Japan.

The name of this marine crab goes to its existence in the water around Japan. The crab is known in Japan as “Taka-ashi-gani” which means “tall legs crab”.

The Japanese Spider Crab has the largest leg span of any arthropod in the world reaching in adult specimens up to nearly four meters with an average length of about 3 meters as measured from the tip of one claw to the other when stretched apart. The average leg span of 1.0–1.2 meters when caught by fishermen. This longest known arthropod is not the heaviest arthropod as an animal of this size weighs only 16-20 kg keeping in mind that the well-calcified carapace of the crab may grow to only around 37- 40 centimeters as carapace width in adult specimens. It may worth to mention that while the walking legs and claws lengthen as the crab ages, the carapace tends to stay the same size throughout adulthood.

The Japanese spider crab has eight long and weak legs which could be lost in some incidences. Reports show that the Japanese Giant spider crabs can survive with up to 3 walking legs missing. However, walking legs often grow back during the successive molts

The Japanese Spider Crab is one of the longest living creatures in the world and is often reported that it may live up to 100 years in its natural habitat. However, other reports indicate that the species generally lives for more than 50 years.

 

Distribution and habitats

Distribution: The Japanese Spider Crab, Macrocheira kaempferi can be found off the southern coasts of the Japanese island of Honshu, from Tokyo Bay to Kagoshima Prefecture.

Habitats: Japanese spider crabs most often inhabit the sandy and rocky bottom of the continental shelf and slope. Adults can be found at depths of up to 600 m, or as shallow as 50 meters. Younger crabs tend to live in shallower areas with warmer temperatures. The spider crab prefers the vents and holes in the deeper waters that are big enough to take it.

 

Feeding habits

The giant spider crab is an omnivorous and scavenges for food. They consume animal materials (e.g. small fish, carrion, aquatic crustaceans and other marine invertebrates) and plant matter such as algae and macroalgae. In nature, they normally do not hunt. Instead, they crawl along the seafloor and pick at dead and decaying matter. Having such sharp teeth enables the giant spider crab to shred and crush food materials.

On the other hand, their slow movement of giant crab on the sea floor makes them an easy target for possible predators even though this is not common. In order to deal with possible predation, crab juveniles may decorate their carapaces with sponges, kelp, or other objects as a means of camouflage as well as protection. Most use their large claws against predators especially the small ones.

 

Reproduction

Like most of the crustaceans, the giant Japanese spider crabs have separate sexes. The mature male and female of the crabs migrate up during the breeding season to a depth of around 50 meters.  During mating, the male crab transfers the spermatophore (a sac containing sperm) into the female’s abdomen using his first two chelipeds. Once the fertilization is done, the female crabs carry the fertilized eggs tight against their bottom portions of their bodies and backs during the incubation period. Mother crabs use their back limbs to shift around the surrounding water in order to provide their embryos with vital oxygen.  Hatching takes place about 10 days of incubation where tiny planktonic larvae emerge. The newly hatched larvae drift as plankton at the surface of sea waters. Those larvae are clear and legless and so they are totally dissimilar to their crab parents. They develop and grow through molting until they get their permanent skin. There is no parental care provided by any of the parents after hatching. A female Japanese spider crab deposits more than 1.5 million eggs annually; however, the vast majority of them do not survive to maturity.

 

Utilization of the giant crab

The Japanese giant spider crab, Macrocheira kaempferi has its importance to the Japanese culture. Also, the economic importance of the spider fishery comes from its utilization as food, aquariums, and even for taking and decorating its carapace.

Fishery of the giant spider crab: The crab fishery is centered around Segami, Tosa and Suruga Bays and they are caught using small trawling nets. The decrease of the crab population has forced fishermen to explore deeper waters to catch them.

Utilization of the giant crab as food: This crab is occasionally collected for food even in small quantities. The crabs are often served as a delicacy during the appropriate crab-fishing seasons and are often eaten raw, salted and steamed.

Giant spider crab in Aquariums: The very unusual shape and large size of the crab is attracting hobbyists who look for one of the most unusual aquatic pets while enjoying gentle nature. In such case, a huge aquarium will be required.

Conservation measures: This crab is not subject to commercial fishery because of difficulties in capturing them in large quantities at their deep habitats.  Hence, crabs are only caught by small-scale fishery implying less damaging actions to their stocks. However, the observed decline in the catch of the crab has led to a few conservation measures that centered on the banning of crab harvesting during the spring, when crabs move to shallower water to reproduce.

References: Wikipedia, Tennesse Aquarium, Encyclopedia of Life, Natural World, Georgian Aquaculture, Pawnation

Japanese giant spider crab

 

 

Permanent link to this article: https://fishconsult.org/?p=10738

Apr 20 2014

Collection of sand crabs in Thailand (facts – collection – consumption)

Credit for the photo and the essential information: Samart Detsathit (Thailand)

Review:  Abdel Rahman El Gamal (the site founder)

The sand crab or mole crab which are known as “Hippoids” belong to the super family “Hippoidea”. These small crabs of 1-5 cm in size are adopted to burrow into sandy beaches near the water throughout most of the world. They are mostly scavengers, eating food and diatoms that wash up on the shore.  Their ability to dig in the sand is a means of protection against possible predators which could be fish, water birds, shore birds, otters and sea lions. The specimens shown in the photo were collected from Thai Mueang beach, Phang-nga bay, Thailand.

Collected crabs could be used as bait or prepared for human consumption in a form of soup broth or as deep fried.

Sand crab (Thailand) 01 Sand crab (Thailand) 02 Sand crab (Thailand) 03

 

 

Permanent link to this article: https://fishconsult.org/?p=10733

Apr 19 2014

Trade of ornamental fish in the Chatuchak Market, Bangkok, Thailand

Photo credit: Deepak Bhusal (Nepal)

Review: Abdel Rahman El Gamal (the founder of the site)

The photos are taken in the biggest market in Thailand for ornamental fish, plants, and aquarium supplies. The market is located at Chatuchak market area in Bangkok.  While there is a time allocated for wholesale business, and for everyone with different time arrangements. Fish are displayed in hanged bags or on the walkway, in tanks, bins and even inflatable kiddie swimming pools. Officials of natural resources carry out check visits to the market to ensure that displayed fish are not protected as well as sizing any illegal trade of fish and reptiles and take necessary legal actions for such violations.

Thailand - Ornamental fish trade Chatuchak Market (01) Thailand - Ornamental fish trade Chatuchak Market (02)

 

 

 

Permanent link to this article: https://fishconsult.org/?p=10728

Apr 16 2014

Feeding of African catfish juveniles grown in high density in Benin (Video)

Credit for the video: Ismael Radwan (Egypt)

Description: Abdel Rahman El Gamal (Founder of the website and the video channel)

The video was taken in a catfish farm in Benin. The high density of catfish is reflected in the dark cloud of fishing moving in the tank. Often, the African catfish (Clarias gariepinus) is raised in high density. This is based on their outstanding tolerance to the farming conditions. However, optimum farming environment must be secured. If one watches closely the vigorous feeding activity, quite a few specimens of much smaller size than the average do exist. If these fish comes from one batch or of the same age, the small size could be magnified by the competition for feed and/or for space. If those fish are much younger, periodic grading is essential to avoid the cannibalism which is a common phenomenon in small fingerlings.

 

 

Permanent link to this article: https://fishconsult.org/?p=10725

Apr 16 2014

Use of concrete tanks in the reproduction of Nile tilapia in Benin

Credit: Ismael Radwan (Egypt)

The photo shows the concrete tanks used in the spawning of Nile tilapia, Oreochromis niloticus as well as the controlled collection of fry and broodstock handling. Tanks are rectangular with 3 x 8 meters while water depth could be adjusted depending on activities. During the spawning, each tank is stocked with 30 females and 10 males with average weights of 150-250 g. However, when ponds are used for holding the broodstock during the resting period outside the spawning season, the number of fish stocked in each tank could increase to 100-150 fish regardless their sex.

Use of concrete tanks in the reproduction of Nile tilapia in Benin

 

Permanent link to this article: https://fishconsult.org/?p=10722

Apr 16 2014

Stimulating the natural environmental conditions for the spawning of common carp using Dubisch method

The credit of the figure: FAO, the artificial propagation of warm-water finfishes

Review: Abdel Rahman El Gamal

The Dubisch method was named after Thomas Dubisch, the fishery inspector who introduced this system which has been used afterwards based on its practically, efficiency, and cost.

The Dubisch method includes facilities, fish and management. The key facility in this method is the “Dubisch Pond”. Often this pond is of relatively small pond with an area of about 100m2. The design and size of this pond help to stimulate the spawning of common carp, Cyprinus carpio.

In order to secure the above conditions, the small size of the pond allows a quick filling and draining as required. Also, this small size implies the use of only one or two spawning set.

The pond has typical structures for water filling and draining. Also, a spawning pond of about 100-m2 area would require a peripheral ditch of about 50 cm deep that is dug adjacent to the main dyke of the pond, to serve as a refuge for the breeders.

The main area of the pond is made to slope slightly toward the ditch and is covered with short grass. When the pond is filled, water will cover the grassy area with a depth of about 30-50 cm water.

Management of the spawning operation:

Pond preparation: this includes the elimination of any left-over organisms. This is done through sun-drying and/or use of disinfectants. The proper screening of water inlet is essential to prevent any entry of unwanted organisms. The long and especially soft grass in the pond should be mowed off before the spawning begins.

 

Pond filling: in order to avoid the accumulation of predatory insect larvae, the ponds are filled up only shortly before the spawning starts. Water used should be of optimum quality for the spawning operation.

 

Stocking the broodfish: The ready-to-spawn broodstock are selected based on established criteria. Two sets of spawners are stocked in the individual 100-m2 Dubisch pond; each set consists of one female and two males. To avoid any disease transfer from the spawners to the embryos and larvae of carp, the spawners receive a prophylactic treatment. The spawners are stocked in the filled ditch and then after the water are gradually allowed into the pond till fully filled. By doing this, the triggering factors to induce the spawning become available which are summarized in:

Good water quality

Rising water

Availability of grass

Bringing the two sexes together (note that before the stocking, males and females must have been stocked separately)

The spawning usually begins shortly after the stocking of broodfish or at maximum in the following day and this could be observed in the vigorous spawning on the grassy area to which the laid adhesive eggs stick to.

Immediately after the spawning, the pond water is lowered and hence the broodstock are directed to the ditch where they are carefully netted out from the pond which is filled up again. Hatching will take place in few days/hours depending on water temperature. The removal of broodstock provides enough safety to the offspring against possible disease transfer from parents and also facilitates the handling of hatched fry which are moved few days after to be nursed in nursing facilities.

These simple facilities have been found effective in the spawning of other fish species such as pike, tench, crucian carp and others.

 

Dubisch pond

 

 

 

 

 

Permanent link to this article: https://fishconsult.org/?p=10718

Apr 15 2014

European eel, Anguilla anguilla (Description, feeding, reproduction, threats and conservation)

Credit of the photos: Glenda Vélez Calabria (Colombia)

Technical review: Abdel Rahman El Gamal

These photos have been taken in the recovery plan of European eel (Spain)

 

Introduction: The European eel, Anguilla anguilla, is a catadromous snake-like species of eels, that belongs to the family “Anguillidae”. This species is a popular food fish of high economic value whether in food fish and/or in the trade of young eels (glass eel).

The European eel is found in water bodies that are connected to the sea in all European rivers draining to the Mediterranean, North and Baltic seas, in the Atlantic south to Canary Islands and parts of Mediterranean North Africa and Asia. The spawning area of the species is in western Atlantic (Sargasso Sea) in the West Central Atlantic. The species has introduced from its native range and stocked in most inland waters of Europe as well as in Asia and South and Central America.

Even though the average life span of the European eels is about 15-20 years, so individuals can live more than 50 years. In general, females live longer than males and grow to be about twice the size.  During the cold months, eels are capable to hibernate.

Description: The European eel, Anguilla anguilla has an elongated shape of an average length that ranges from 60–80 cm. However, they may reach a length of 1 m and even 1.5 m in exceptional cases. They have a tough and slimy skin with small, minute and elliptical scales embedded in the skin. Their gill openings are small. The eel has one pair of small and rounded pectoral fins but no pelvic fins. They have a visible lateral line.

Feeding: European eels are nocturnal opportunist carnivores. In nature, they eat a variety of fish and invertebrates especially molluscs and crustaceans, and will also scavenge on dead fishes. As they migrate for spawning, its food are obtained from the aquatic fauna whether in freshwater or in marine. The ability to stay out of water –as conditions permits- enhances their feeding ability and allows them to feed on other organisms such as worms. Small eels feed on insect larvae, molluscs, worms, and crustaceans.

In eel farms whereas glass eels are stocked in farming operations, the transition from natural food such as worms to artificial feed (i.e. paste and/or pellets) is important for replacing the natural food with a nutritionally rich dry/artificial diet. In general, eels demand extraordinary high quality of feeds in regard to nutrient specifications and digestibility.

Reproduction and life cycle: The life history of the European eel’s was a mystery for centuries especially in regard to their trip to spawn and the back trip of their progeny to parent’s home.

It is documented that the Danish researcher Johannes Schmidt was the first who pointed out in the early 1900s that the Sargasso Sea is the spawning grounds for the European eels.

Eels reach their sexual maturation in freshwater after 5–20 years. Sexually mature eels are characterized by their larger eyes, their silvery flanks and white belly and are known in this stage as “silver eels”. Mature eels migrate from European rivers and estuaries to the Sargasso Sea in the West Atlantic for spawning. This trip covers great distances which could range from 5,000 – 6,000 km.

Mature females may spawn up to 3 million eggs per/kg of her body. Adults die after spawning and egg fertilization whereas fertilized eggs hatch into planktonic, transparent ribbon-like larvae known as “Leptocephalus” which drifts from the sea back to the continental waters. When the “leptocephali” are just approaching the European coast in about 200-300 days, they metamorphose into a transparent larval stage (6-8 cm length) called “glass eel” that results in a shortening of the body and formation into a more cylindrical shape.  As “glass eels” continue their trip in estuaries and lakes and gain pigmentation, they metamorphose again into pigmented “elvers” which move into freshwaters. The elvers are miniature versions of the adult eels. As elvers grow, they turn into “yellow eels” based on the brownish-yellow color of their sides and belly. Afterwards, yellow eels in freshwater undergo a long feeding period and so growth for a period of 6-12 years in males and 9-20 years in females ending by sexual maturation, changing color into silvery (silver eels), developing bigger eyes and accumulating higher body fat contents. This phase is their last summer in freshwater before being stimulated by lower temperature and higher salinities and hence performing their spawning trip to the Saragossa Sea. During the spawning trip, the gametogenesis occurs.

Threats and conservation efforts: Overfishing of glass eels in specific European waters as well as on downstream migrating eels (silver eels) across Europe is considered a significant threat to the species. Since there is no artificial reproduction of eels, the shortage in glass eels will lead to a subsequent decline in the catch of adult eels. The reports show that the recruitment of glass eels has drastically declined from 1980 onward, showing in 2000 a 95 to 99% decline compared to prior 1980. This decline in recruitment will translate into a future decline in adult stock, at least for the coming two decades.

Noting the longevity of the species, and the extremely depleted stocks, the restoration of the stocks is expected to take several generations depending on the protection level especially in the absence of artificial reproduction.

The sources of threats include overfishing (to adults or glass eels), dams (may block the migration routes), disease (e.g. nematodes), pollution and loss/degradation of spawning grounds.

Because the decline of eel stocks is likely to continue, the protection and conservation of eels became necessary. The conservation strategy is being implemented in concerned countries through governing regulations and recovery plans.

An example to the actions taken at the international level, is listing the species in the Appendix of CITES in 2007 which implies some actions like the exporting permit to ensure that the export of eels will not be detrimental to the survival of the species. Some states issued their own regulations such as banning the importation, sale, or culture of live eels in California (USA).

The recovery of the European Eel stocks targeted to permit the escapement to the sea of at least 60% of eels less than 12 cm in length; caught eels of this length category should be reserved for restocking and not for aquaculture. The conservation measures include reducing commercial and recreational fisheries, improving habitats and making rivers passable.

References: IUCN Red List, Encyclopedia of Life, FAO, Wikipedia

European eels (adult) European eels (glass)

Permanent link to this article: https://fishconsult.org/?p=10716

Apr 12 2014

Daphnia (Characteristics, feeding, reproduction, reactions to environmental stress)

Photo credit: Manuel Cano Alfaro (Guatemala)

Review: Abdel Rahman El Gamal

This specimen of Daphnia belonged to the fauna of Lake Amatitlan, Guatemala

Introduction: Daphnia is a large genus comprising over 200 species of small freshwater crustaceans that belong to the family Daphniidae and the order “Cladocera”. These small crustaceans of 1–5 millimeters in length are commonly called water fleas due to their jerky swimming motions resembling the movements of fleas. Daphnias live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers. Some types of Daphnia can be seen with the human eye, while others must are microscopic. This is represented by Daphnia magna and Daphnia pulex for the large and microscopic species respectively.

Key characteristics: Depending on the species, Daphnia ranges from 0.5mm to 1cm long. In most Daphnia species, the body has a ventral gap in which the pairs of legs lie. Their outer carapace is transparent, so many internal organs can be seen, even the beating heart. On the head there is a compound eye and a pair of antennae, which are used for swimming. Females are usually larger than males and have a brood chamber under their outer carapace where eggs are carried.

Feeding: Daphnia uses its third pair legs to filter the water to keep the large unabsorable particles out, while the other sets of legs beat the water and create the current which brings in the appropriate Daphnia’s food of unicellular algae, protists and bacteria into their digestive tract.

Reproduction: Most Daphnia species have a life cycle alternates between asexual (Parthenogenic) reproduction and sexual reproduction. Under favorable conditions, Daphnia females reproduce asexually in which the laid eggs hatch into exact clonal copies of their mother. Following each molt, the mature female lays number of eggs which vary according to species from as few as 2 to as much as 20 eggs or more; these eggs develop without fertilization into females. On the other hand, when food turns scarce, Daphnia reproduce sexually in order to produce genetic variation and increase the chance of species survival. Under typical conditions, eggs hatch after about a day, and remain in the female’s brood pouch for around three days before being released into the water, and pass through a further 4–6 instars over 5–10 days before reaching an age where they are able to reproduce.

Daphnia and food chain: Daphnia are an extremely important part of aquatic food chains. They eat variety of primary producers such as algae, yeast, and bacteria. Many animals eat the Daphnia to survive. Those include tadpoles, salamanders, aquatic insects, and many of small fish species. Hence, the decline in Daphnia populations can lead to algae overgrowth and vice versa which in turn could affect fish production.

Reactions to environmental stress: Daphnias are very fragile animals and are extremely sensitive to water toxicity to which they exhibit number of natural responses leading to the use of Daphnia as a test or indicator organism in the environmental monitoring program and for ecotoxicological studies especially some of their response such as their heartbeat could be seen through their transparent outer carapace. Daphnias are known to be very sensitive to chlorine and various heavy metals.

Daphnia and hemoglobin production: Daphnia do not need to maintain a high level of hemoglobin to survive. However, they are exposed to low oxygen conditions (hypoxia), they can increase hemoglobin production turning them red as seen through their transparent carapace. Their ability to produce hemoglobin provides them a survival advantage in hypoxic water conditions. It is interesting to note that Daphnia with high hemoglobin content have access to food sources found in low oxygen areas giving them another advantage.

Daphnia in Lake Amatitlan (Guatemala)

 

 

 

Permanent link to this article: https://fishconsult.org/?p=10710

Apr 10 2014

Culture of variety of fish species in off-shore cages and feeding systems

Credit: Huseyn Ek (Akuakare, Turkey)

The photos shows typical off-shore cages use to grow variety of fish species including gilthead seabream, European seabass, trout, meagre, carp, tilapia, and sturgeon. As expected, cage productivity and growing seasons should vary according to farmed species whereas average productivity could be 10-12 kg/m3 for seabream, seabass and trout increasing to 20-30 kg/m3 for tilapia and carp. The length of the growing season also varies from as short as 6 months for tilapia and trout, increasing to 12-18 months in regard to seabream and seabass, then 16-24 months for carp while 3-4 years will be required for sturgeon. One of the photos shows a feeding barge that automatically supplies individual cages with their specific feeding rates.

Off-shore cages (01) Off-shore cages (02)

 

 

 

 

Permanent link to this article: https://fishconsult.org/?p=10704

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