The photo shows the facilities what are in use during the hormonal treatment of Nile tilapia, Oreochromis niloticus. One may notice that the relatively small size of tanks which enables the matching with the possible number of treated tilapia fry keeping in mind that the fecundity of Nile tilapia (no. eggs/female) is most likely in hundreds and/or reaching/exceeding the thousand. Therefore, the tanks used during the treatment consider the number of treated fry by batch. In this particular facility, the under-ground water is the only water source and so, the trickling devices above the tanks in an attempt to aerate the water especially the underground water is lacking oxygen.
The video was taken in the Sea World, San Diego, USA
Review: Abdel Rahman El Gamal (Founder of the website and video channel)
General: The short-nosed unicornfish (Naso brevirostris) which belongs to the family Acanthuridae has other names including spotted unicornfish, and brown unicornfish. In general, it is a very peaceful fish whether in the wild or in captivity in tanks. The species is not targeted in multi-species fisheries and hence, the conservation category is “least concern” according to the IUCN red list. The short-nosed unicornfish can live up to 25 years.
Description: Unicorn fish has elongate and oval body with a short snout. Their name comes from the horn which star growing at a particular age/size (15-25 cm) and turns into a pronounced horn on the front of their heads in their adulthood. The species has also two sharp spines located on each side of its body, next to the caudal fin. These are used for self-defense. The maximum length of the species has been reported to be 60 cm. Unicorns are very active swimmers.
Geographic range and habitats: The short-nosed unicornfish inhabits variety of world tropical waters. The species occurs on coral reefs and rocky shores at various depths which could range from 0 – 45 meters (usually 5-30 m) for adults. Juveniles inhabit sheltered habitats with seagrass beds at depths which can reach 20-meters.
Feeding habits: Juveniles and sub-adults of unicorn fish feed on benthic and filamentous algae; adults feed primarily on zooplankton. It is believed that the change in food habits may be associated with the development of the long horn which would inhibit grazing on algae except on the boarders of reefs as horns do not get in the way. They can feed also on pelagic fish larvae.
In aquariums, unicorns are grown on aquarium foods which include live adult brine shrimp, larger shrimps, live marine algae, boiled broccoli and variety of worms.
Reproduction: Unicorn fish are of separate sexes that reach their sexual maturation at about 25-cm length. It is believed that the species spawn in pairs and may form spawning aggregations in the spawning grounds. The mating pair swim along together, touch bellies and then the female eject her heir pelagic eggs that hatch –after fertilization by male’s sperm- into relatively large larvae which stays in the pelagic environment for about 90 days before moving to more appropriate environments.
References: Wikipedia, Discover Life, Wakatobi, Encyclopedia of Life
The photos show the use of nymph as a substrate for the production of the earthworm. The use of worms allows the production of compost and simultaneously stabilizes the presence of heavy metals and some other chemicals which could present in the plants. The role of the earthworm stops at the cleaning process of produced compost and it is not recommended to use the earthworms itself as protein supplement to avoid any bioaccumulation possibility of heavy metals and/or other harmful substances in the tissues of the earthworms. The earthworms are commercially produced and sold to compost producers.
Salinity measurement could be determined through several approaches including the refractive index using refractometers. The principle of the refractive index is based on the light refraction through liquids; the more dissolved solids in water, the slower light travels through it. The amount of bending (refraction) is related to how much salt is dissolved in the water.
Refractometers which are handheld devices measure the difference in light refraction between solutions. The amount of salt dissolved in a given quantity of water changes its refractive index, allowing water salinity to be measured optically.
Calibration: The calibration of the refractometer is done through placing two to three drops of distilled water on the prism before closing the cover plate and start reading. If the refractometer reads zero, no calibration will be needed. If the refractometer reads other than zero, the calibration screw should be turned the scale until it reads “0” and hence the calibration is complete.
Measurement: To check water salinity using a refractometer, 2-3 drops of water are placed on the optical prism of the held-level refractometer. Afterwards, the reading of the sharp-looked numbers that correspond with separating line between the two fields (light/dark) of the meter would measure the salinity in gram/liter of the water sample.
The recovery plan of the European eel, Anguilla anguilla, includes an review of the creels that had been previously placed in the National and Natural Park Doñana as well as also in the Guadiamar Green Corridor. This activity is carried out in order to keep track of the biological conditions of adult eels that start their migration process towards the sea. The photo shows the placing of a creel in a predetermined location.
The photos show simple fishing gears (traps) which are made of locally available materials. Trapping is a favored fishing practice to artisanal fishermen especially whenever fishery stocks are abundant as well as when the right location for placing the traps is chosen. This is in addition to the low investment in trapping.
Tilapia fingerlings when reaching a weight of about 15-20 grams can be sexed by looking at the genital papilla which is located behind the anus. The genital papilla has a single opening in males (for urine and milt) while females have two openings; one for urine and one for eggs. Training will be required in order to achieve better results; however, some farm workers are more skilled than others in this operation. The use of colored dyes will make it easier to sex tilapia fingerlings. The application the dye such as gentian violet, India ink, halcyon blue or indigo to the papilla with a soft brush or cotton swab will outline the male and female openings.
The photo shows a fishing boat in Bolivian water and the capture of leopard catfishes, Perrunichthys perruno using line fishing using a bait of tarpon meat. This medium-size species does not enjoy a great commercial value and is only used for local consumption. This species is the only member in the genus Perrunichthys.
In this fishery community, women and children receive the fish catch from fishermen who belong to the community for preparation. In this particular photo, children of different ages are handling several specimens of Pacu, Colossoma macropomun. In such remote areas whereas the city electricity is lacking fish are usually consumed fresh especially when the transportation from and to these areas are limited to waterway. Excess fish are dried for remote markets.
Review: Abdel Rahman El Gamal and Manuel Cano Alfaro
The video has been taken in one of the few tilapia hatcheries in Guatemala. This particular hatchery provides tilapia fingerlings in the coastal area. The video shows the hatchery facilities including earthen ponds, metal tanks and concrete tanks. The sampling of tilapia fingerlings has been shown in this video ending by selling fingerlings which are packed in plastic bags. Feed samples and sizes indicate the size groups of tilapia maintained on the hatchery including broodstock, fry and fingerlings.
