Sep 21 2013

Garden eels, Heteroconger sp. (Description, feeding – reproduction) – Video

This video was taken at Monterey Bay Aquarium, California, USA

Introduction and description: The garden eels belong to the conger eel family, Congridae. They are also known as Hass’s Garden Eel. These small thin, tube-like eels burrow into the sand on the sea floor, usually near coral reefs in tropical water. Since they tend to live in large groups, the many eel heads they poke from their burrows will resemble the plants in a garden or a field of seagrass waving softly in the gentle current. They are shy animals and will disappear into their burrows upon approaching a scuba diver which make its photographing a difficult task. Although they are very small compared to other eels but have large eyes indicating their reliance on their sight to capture food. They can grow to over about 30-cm long, but what we see is only part of their bodies as the lower part (with the tail) is buried in the sandy burrow. Garden eels carry no threat to humans, and hence they are kept as pets in salt water aquariums. There are two species of garden eel, Heteroconger cobra, and the spotted garden eel, Heteroconger hassi.

Burrowing behavior: They dig these burrows with their hard-tipped tails using a gland in their tail which secretes a slime that glues the sand in the hole in place and hence keeping the burrow against collapse. Once, the burrow is made, eels rarely leave their burrows completely. However, exposed up-portion of eel body will enable them to feed and to mate.

Feeding habits: They eat without leaving its burrow. With their head exposed, they capture zooplankton as it drifts by in the ocean current. As expected, the stronger the water current, the more abundance will be the food. If the food gets scared, a garden eel takes its whole body into the burrow closing the burrow with a mucus plug to protect itself.

Reproduction: A garden eel may leave its original burrow during spawning season and make a burrow closer to its chosen mate. When mating, the two eels entangle their upper bodies together, while their lower bodies remain in their individual burrows. A female lays her eggs which are fertilized by the male. Fertilized eggs are released into the current. Eggs and larvae float in the current near the surface of the open ocean until the young eels grow large enough to swim down to the sandy floor and make burrows of their own. Immature eels are completely black.

Permanent link to this article: https://fishconsult.org/?p=9273

Sep 20 2013

Green moray eels, Gymnothorax funebris (Biology, geographic range, and adaptation) – Video

Video credit: Glenda Vélez Calabria (Colombia)     Technical review: Abdel Rahman El Gamal  

This video was taken in mundo marino and te mostramos lo que pasa en el fondo, Colombia

Introduction: The “Green moray eels”, Gymnothorax funebris are also known as “green conger”, “green congo”, “green eel”, and “olive-green moray eel”. They belong to the family Muraenidae. Based on few documents on green moray eels, it is thought their lifespan in the wild is between 8 and 30 years. A single record indicated that a green moray lived 85 years in captivity. They may be found in public aquariums while not recommended for smaller aquariums because of their escaping ability. Even though they are not common as food fish, within their native range they are eaten by some indigenous peoples. However, there is considerable risk of contracting ciguatera poisoning from this species.

Geographic range

Range: Green moray eels, Gymnothorax funebris, occur in the western Atlantic Ocean from New Jersey to Bermuda and the northern Gulf of Mexico, south to Brazil. They are most common throughout the warm waters of the Caribbean Sea and the Bahamas. These eels make small migrations to spawning sites.

Habitats: Green morays are benthic and solitary species found along shallow rocky shorelines (to a depth of 30 m), intertidal areas, coral reefs, mangroves, seagrass beds, and other areas of sandy or muddy bottoms.

Description: Green moray eels, Gymnothorax funebris, are one of the largest of the moray eels. The body of green moray is muscular with a long dorsal fin that extends down the length of the body starting from the head and ending in a short tail fin. On the average, the length of adult green moray is about 180 cm (ranges from 90 – 150 cm) with an average weight of about 13 kg. Green eels can reach about 250 cm of weight up to 29 kg.

Green Moray has no scales and instead has a smooth brown body. The Green Moray’s body is coated with a layer of protective mucus layer of a yellow color that when mixed with the brown or grey color of eel’s skin, results in a green appearance, for which the animal is named. The species does not show sexual dimorphism as both sexes are alike.

Green eels have a large mouth with a single row of sharp, prominent teeth on the bottom jaw and two rows of teeth on the upper jaw. They also have a third row of curved teeth on the roof of the mouth that helps slippery fish go down the throat. Their structure of their jaws allows them to open and close their mouths both horizontally and vertically which permits them to eat very large items.

Adaptations and habits

Swimming: Moray eels swim by undulating their flattened bodies into lateral waves. Their compressed bodies and well-developed dorsal fins increase their swimming efficiency and they can swim background as good as forward.

Sense: These nocturnal hunters have poor eyesight so they use their sense of smell to find prey. Since the nasal apparatus area is longer in this eel than in other fish, their sense of smell is more acute.

Camouflage: The green color of moray eels is a form of camouflage that enables the eels to hide during the day in rocky crevices waiting for prey to swim by before grabbing it.  They forage in open at night.

Respiration: Green eel continually opens and closes their mouths slowly to force water through their gills. This gaping motion is necessary for respiration.

Social arrangements: Moray eels are benthic and generally solitary animals coming together only for spawning. They are normally gentle and curious and are not threat to human. However, they will turn aggressive when defending their territories or when hunting for food. Their bites are painful and dangerous.

Territorialism: Green eels tend to live and occupy a specific reef for many years.

Feeding behavior: Green morays are nocturnal predators with poor eyesight that primarily use their sense of smell to hunt at night for fish, crabs, cephalopods, octopuses, shrimp and other eels. In aquariums and zoos, green morays are often fed live fish, squids and meaty foods.   

Life cycle: Although there is not much is known about the reproduction of green moray eels, it is believed there are common features with moray eels. For the sake of this review, it could be stated that the green moray eels are oviparous meaning their larvae “leptocephalus” that hatch from eggs.

References: Animal Diversity Web, Marine Bio, Wikipedia, Marine Species Identification Portal, Ashland University, Encyclopedia of Life, Fish Base.

 

 

Permanent link to this article: https://fishconsult.org/?p=9269

Sep 20 2013

Success story: Backyard hatchery of freshwater prawn (Macrobrachium rosenbergii) in Thailand

This type of hatcheries looked attractive to particular segment of producers who target profitable and small-scale operations especially when could be operated by family members whenever possible. Backyard hatcheries were able during 1980s to provide the required numbers of post larvae to freshwater prawn farms.  The attached photos were taken during my visit to Thailand during March 1988. The concept of the freshwater prawn backyard hatchery could be extended to other species whenever found feasible.

Backyard hatchery (Thailand) 01 Backyard hatchery (Thailand) 02

 

 

Permanent link to this article: https://fishconsult.org/?p=9262

Sep 20 2013

Historic information: When fishing in iced lakes to feed the dogs is of top concern to Eskimos (1934/35)

Information source: Edward Shackleton, 1936, Arctic Journey, the story of the Oxford University Ellesmere Land Expedition, Publisher: Hodder & Stoughton Limited.

Introduction to this post: When distilling this piece of information for posting, I intended to share with you few issues of specific relation such as the fishing in iced lakes (e.g. Lake Hazen) whereas the thickness of ice was 4-5 feet. In this post, feeding the dogs has been highlighted as key issue in this cold environment whereas the fitness and general health of dogs represent a vital role to the masters from human. You may agree with me about the unfair and seasonal treatment dogs received when their feeding was less during summer when they were less needed, while dog feeding was a top concern during winter when the need was great to pull the human sledge over ice.

If you are interested in the topic, please go to the following link and you may see the dogs driving the sledge in the attached photo:

[gview file=”http://fishconsult.org/wp-content/uploads/2013/09/Historic-information-Fishing-in-iced-lakes-to-feed-the-dogs.pdf”] Eskimo fishing for dog feeding

 

 

Permanent link to this article: https://fishconsult.org/?p=9257

Sep 19 2013

Historic information: Eskimo’s hunter’s boat “kayak”

Source of the photos: Edward Shackleton, Arctic Journeys. 1936

Review: Abdel Rahman El Gamal

Kayak is a small, light, relatively narrow, human-powered boat primarily designed to be manually propelled by using a double paddle.

Kayaks which mean “hunter’s boat” or “man’s boat” were created thousands of years ago by the Inuit and Aleut tribes (formerly known as Eskimos) of Arctic North America.  These early kayaks were used during summer months primarily for navigation, hunting and fishing in sub-Arctic regions of northeastern Asia, North America and Greenland. Seals were the main hunting target, though whales and caribou were important in some areas.

These first kayaks were constructed from sealskins or walrus skins stretched over a frame made of driftwood or whalebone. The smooth and flexible skin glides silently through the waves. The tribes used whale fat to waterproof the vessels. To improve the buoyancy of kayaks, they used air-filled seal bladders. The tanning of the hides and the sewing of the outer hull were the responsibility of the Eskimo women. Depending on the frequent use of “kayaks”, the outer skin had to be renewed at least every one-two years.

It is interesting to know that the Eskimo kayak builders while designing the boats, they had in consideration the span of the outstretched arms, and the width of the builder’s hips. Based on that, typical dimensions of kayaks were about 5.2 m long by 51–56 cm wide by 18 cm deep. There were slightly larger size of the same boat. The design ensures maximum safety of the boat user through securing a sustainable upright on rough waters and enable users regaining their position when the kayak turned over and hence help Eskimos avoid swimming in such extremely cold water.

It may worth mentioning that in 1936, the Olympics included kayak racing as a part of the Olympic Games in Berlin.

Eskimo boat 01 Eskimo boat 02

 

 

Permanent link to this article: https://fishconsult.org/?p=9249

Sep 18 2013

Historic information on the processing of eels in Comacchio, Italy

Source of the photo: Les merveilles de la science – Chapter Pisciculture, by: Louis Figuier.

Publisher: Furne, Jouvet et Cie.  Year : 1869

Caption of the photo (in French): Manufacture pour la preparation et la salaison des poissons de la lagune de comacchio

Review: Abdel Rahman El Gamal

The figure shows a room in a factory where the Comacchio eels is prepared. The description of the figure and operation in the source are in French.

The more in depth review tells how these facility were used in the production process of cured and roasted eels. In Comacchio the marinating of eels goes back centuries and took place at processing factories. The eels used to reach the processing factory alive as transported in covered boats. In the factory, eels were handled by women and men according to different tasks that included cutting, spiking, cooking over open flame fire, then packing the product in a vinegar and saltwater brine. It may worth mentioning that the present authority of Comacchio County commissioned a restoration program for the ancient preparation of eels as practiced in the old days.

Historic processing of eels in Italy

 

 

Permanent link to this article: https://fishconsult.org/?p=9245

Sep 17 2013

Farming practices of freshwater prawn, macrobrachium rosenbergii in the Philippines

Credit: Hannibal M. Chavez (Philippines)

The present practice of freshwater prawn farming is done in cages in the lake. This proved to be a viable technology since the culture period is relatively shorter (160 days) compared to pond culture (180 to 240 days) to achieve a marketable size prawn.

Providing shelters to prawn at 1 pc per m3 reduce the frequency of agonistics interactions and stress resulting in increased survival rate from 80% to 85% and mean size of about 50 g upon harvest.

Freshwater prawn in the Philippines (01) Freshwater prawn in the Philippines (02)

 

 

Permanent link to this article: https://fishconsult.org/?p=9238

Sep 17 2013

Southern Guitarfish, Rhinobatos percellens (distribution, description and biology) – Video

Credit of the video: Glenda Vélez Calabria (Colombia)

Description: Abdel Rahman El Gamal

This video has been taken in mundo marino and te mostramos lo que pasa en el fondo, Colombia

Introduction: Southern Guitarfish, Rhinobatos percellens is also known as “Chola guitarfish”, or “Guitarra chola” and other names. It seems there is commercial fishery for this species which is often captured as bycatch in commercial and artisanal fisheries in some parts of South America. The reason for that is the inferior quality of fish flesh. However, some of caught fish are salted and consumed in some regions. Aquarium trade utilizes a part of southern guitarfish stocks.

Distribution and habitats: Southern guitar, Rhinobatos percellens is found in Western Atlantic and Eastern Atlantic. The species lives on shallow and soft bottoms of the continental shelf at depths of 0 – 110 m.

Description: The southern guitarfish are characterized by their elongated body as intermediate between those of sharks and rays with a flattened head and trunk and small ray like wings. They have shorter nostrils with no enlarged tubercles on the tip of the snout.  The color is olive gray, reddish brown or chocolate brown above; an extensive pale translucent area on either side of rostral ridges. Darker brown spots or blotches on sides. Their lower surface is pale yellowish, greyish or dusky white while the tip of the snout has a more or less conspicuous sooty blotch, either solid or more or less interrupted. The common total length of guitar fish is about 70 cm and can reach to up to 100 cm as a total length.

Reproduction: The southern guitarfish are Ovoviviparous with embryos feeding initially on yolk, and then receiving additional nourishment from the mother by indirect absorption of uterine fluid enriched with mucus, fat or protein through specialized structures. The mean diameter of the largest oocyte was about 30 mm.  The fecundity ranged from two to 13 embryos (mean of five embryos). Total length of born fish is about 20 cm.

Threats: the species has been placed in the IUCN Red List as “Near Threatened – NT”.  The threat is based on the high exploitation level of the species that resulted in the quantities taken as bycatch in an intense fishing of commercial and artisanal fisheries.

References: Encyclopedia of Life (EOL), Fish Base, Shark Reference, Science Alerts Social Network, SearchFish.org

Permanent link to this article: https://fishconsult.org/?p=9230

Sep 17 2013

Glass fish (Introduction – distribution – biology – painted glass fish) – Video

This video was taken in freshwater aquarium, the Sea World, San Diego, California, USA

Introduction: The fish is so named because of its translucent flesh whereas all the organs of the fish are completely visible like their bones etc. So due to this nature they gain some name in the aquarium world. There are several species of glass fish. Out of which, two species are shown in the present video. The first which is thinner in shape is just named glass fish (Parachela oxygastroides), while deeper-bodied fish are Indian glass fish (Parambassis ranga). There is a great similarity among various glass fish. Glass fish is not important as a food fish for humans, but is very common in the aquarium trade.

Distribution: Glass fish are freshwater, pelagic and tropical fish. They live in rivers and lowland wetlands including peat canals. These fish are distributed mainly in Asia, while through aquarium trade, it accessed further geographical zones.

Feeding habits: In nature, glass fish feeds on zooplankton, insects and small fish. It is in turn prey for larger fish, including snakeheads.

Reproduction: Glass fish are egg layers whereas female lays about 200 eggs which are fertilized by male. In nature, eggs are found among plants. Fertilized eggs will hatch in about 24 hours and will turn free swimming in another 3-4 days. No parental care is expressed during incubation or hatching.

Social behavior: They are peaceful and schooling fish and so individuals –if not kept in groups- they become shy and nervous.

Painted glass fish: Unfortunately, this action represents a fraud action when fish keepers are not aware about the painting process before watching the fading of color over time (depending on the type and dose of the dye, it often start metabolizing in 4 months. The life span for normal unpainted specimens may go to three to four years while this is often shorter for artificially colored fish depending on the side effects of painting if occurs. Painted glassfish: in order to attract hobbyists, glass fish is often painted. This is done through injecting with a fluorescent dye into the fish’s transparent tissue.

 

 

Permanent link to this article: https://fishconsult.org/?p=9223

Sep 15 2013

Atlantic tarpon – Megalops atlanticus (Distribution – biology – conservation) – Video

This video was taken in June 2012 at the World of the Sea aquarium, Sea World, San Diego, California, USA

Introduction: Atlantic tarpon, Megalops atlanticus that belongs to the family Megalopidae is also known as the silver king and Sábalo in Spanish. Although this species has no commercial value as a food fish due to its bony flesh, it is a premier sport fish species not only because of their size, but also because of their fighting spirit when hooked. When they occur in high abundance, tarpons would be of economic significance. Their average life span is about 50-55 years for females and 30-40 years for males. Being a prized game fish, tarpon would be present in fishing festivals. In fact, there is a special International annual tarpon Fishing Contest that is held in Tecolutla on Mexico’s Costa Esmeralda. The tarpon is the official state saltwater fish of Alabama.


Distribution and habitats: The Atlantic tarpon (Megalops atlanticus) populates a wide variety of habitats, but are primarily found in coastal waters, bays, estuaries, mangrove-lined lagoons and rivers on both sides of the Atlantic Ocean, typically in tropical and subtropical regions, though it has been reported as far north as Nova Scotia and the Atlantic coast of southern France, and as far south as Argentina. They are also found throughout the Gulf of Mexico and the Caribbean, and in the Eastern Central Pacific off Coiba Island. The species migrated through the Panama Canal from the Atlantic to the Pacific and back. The normal habitat depth for tarpon extends to 30 m.   

Tarpons tolerate wide ranges in salinity (0 – 47 g/l) throughout their lives and hence they often enter river mouths and bays and travel upstream into fresh water. The modification in their air bladder allows tarpon to inhale atmospheric oxygen and hence to tolerate oxygen-poor environments.

In regard to temperature, tarpons prefer water temperatures of 22 to 28°C, below 16°C they become inactive, and temperatures below 5°C can be lethal and so tarpons seek warmer refuges in deeper water whenever temperature drops to such risky levels.

Description: Tarpon, Megalops atlanticus are large, beautiful, fish that can reach up to 2.5 m and weigh up to about 160 kg for female with males generally smaller. They have bluish-gray color on their dorsal side with very bright silvery sides and belly. Tarpon has a large and superior mouth with the lower mandible extending far beyond the upper jaw. Tarpon have very large scales with 40-48 scales along their lateral line. Tarpon possess a swim bladder attached to their esophagus which enables them to live in oxygen-poor (hypoxic) water.  Tarpon also uses its swim bladder in producing sound in the form of thumps in case of attack.  

Feeding behavior: During their larval stages, tarpon larvae absorb nutrients directly from seawater. As fish grows reaching small juveniles, they consume zooplankton (copepods and ostracods), insects, and small fish while adult tarpon become carnivorous and prey on midwater fish, shrimp and crabs. Tarpon feed during both the day and the night. Because of their small teeth, they generally swallow their prey whole. The ability of tarpon to tolerate low dissolved oxygen levels due to the structure of its swim bladder, the species would enjoy a predatory advantage when oxygen levels are low. On the other hand, different life stages of tarpon are vulnerable to predation that range and include from zooplankton, small fishes, piscivorous birds, and sharks.

Reproduction:  Tarpon reach sexual maturity at 6-7 years of age and By 10 years of age; all females were found to be sexually mature.  They breed offshore in warm, isolated areas. On the average, adult female tarpon produces more than 12 million eggs at once in an annual spawning cycle.

Threats and conservation:

Threats: Tarpon fishery is exposed to variety of threats. The catch and release fishing by recreational anglers may be a source of adult tarpon mortality even at low rate. Habitat degradation due to whatever reasons (e.g. pollution) represents a significant threat to tarpon fishery. Tarpon estuarine fishery may be threatened by runoff from agriculture and urbanization.

Conservation measures: According to situations and types of threats, the followings are examples of conservation measures which are taken in different tarpon fishery:

Declaring tarpon as a game fish in South Carolina in 1991 led to not only the banning of the sale of tarpon but also limiting recreational anglers to a possession limit of one fish per person per day.

In Florida and Alabama, a special permit is required to kill and keep a tarpon.

Promoting and creating awareness on the conservation ethics upon the handling of tarpon should go side by side with fishermen education on the best practices when releasing the fish.

References: Florida Museum of Natural History, MarineBio, NAS – Nonindigenous Aquatic Species, Wikipedia

 

Permanent link to this article: https://fishconsult.org/?p=9216

Load more