The photos show the sampling of plankton in Lake Nasser using plankton nets equipped with flow meters (shown in the middle). The flow-meter measures the quantity of water filtered through the plankton net and hence enables relating the results to units of water. There are two types of plankton nets based on their mesh size; the 0.1-mm-mesh net is used for all plankton types (phyto and zooplankton), while the 0.3-mm mesh net targets mainly zooplankton.
The method used in this analysis adopts the vertical haul in which the plankton net is lowered from a stationary ship in the water till reaching the desired depth then immediately pulled upward. The flow-meter measures the quantity of water filtered through the net. Afterwards, the collected plankton is processed (e.g. preserved, enumerated) as planned in the analysis (e.g. qualitative, quantitative, wet weight, dry weight) and relates the results to a unit of water. In Lake Nasser, water is analysis at depths that range from surface water till 20-meter depth at 5-meter intervals.
Credit for the photos and information providing: Sherif Sadek and Mohamed Sabry (ACO)- Egypt
Reporting: Abdel Rahman El Gamal
The photos are related to the shrimp sampling during the grow-out in shrimp ponds in this particular shrimp farm located along Port Said-Damietta road, Egypt.
Shrimp are sampled biweekly for key purposes including the assessment of growth rate, homogeneity and to get an idea about survival rate as well as disease incidences if any. Cast nets are used in the sampling at a rate of 15 castings in each sampling per hectar. While most samplings are done in the feeding zones, remaining castings are done in the far end of the grow-out pond.
The last shrimp sampling is done about 3-days before the suggested harvest day to ensure that the targeted weight has been achieved considering the market demand and pricing system.
One of the photos show the homogeneity of sampled shrimp while the second photo shows the condition of sampled specimens.
Credit for the photos and information providing: Sherif Sadek and Mohamed Sabry (ACO)- Egypt
Reporting: Abdel Rahman El Gamal
Because the specialized shrimp feed is expensive especially when the feed used is imported, efforts are spent to minimize the feed waste caused by overfeeding and in the same time provide the proper quantity of feed for best growth rate. Shrimp in existing ponds are fed for five times/day; two of which are performed during day time while three feedings take place during night. In that regard it needs to emphasize that shrimp is the species targeted for feeding while it is believed that the production economics should be investigated if mullets which share the same pond are consuming much of this expensive feed. Thus the 60% of night feedings is assumed to be the share of shrimp which are capable to feed at night while mullets will not feed during night – theoretically.
Feed is provided in feeding trays which are placed at intervals along one of pond lengths. Two hours after feeding, feeders are physically checked to determine the status of feed consumption and /or leftovers to be utilized in adjusting feeding rates. In the present farm, 15 the 1-ha pond is furnished by 15 feeding trays shown in the photo; the second photo shows feed samples for the shrimp.
The protein and fat contents of shrimp feed throughout the grow-out are 34% and 15% respectively. In this particular farm, the size of feed particles (crumbles/pellets) used increases as shrimp grows and includes 0.6, 1.2, 2.2, and 2.5 mm.
This video was filmed in Alexandria marine aquarium (National Institute of Oceanography and Fishery), Egypt
Clownfish includes a group of species that belongs to the family Pomacentridae. These species whether caught from the wild or bred in captivity make up about 40% of the global marine ornamental trade. They are about 30 known species which are native to warmer waters and are found around tropical coral reefs; most of which live in the shallow waters of the Indian Ocean, the Red Sea, and the western Pacific.
These fishes are characterized by their bright yellow to orange color with three distinctive white bars across its body. They are among the most recognizable reef-dwellers. Their average length –as reported- ranges about 11 cm.
Feeding habits: Clown fish are omnivorous animals that they eat a wide range of food such as algae, plankton, molluscs and small crustaceans. They also feed on left-over or undigested food from their host anemones.
Clownfish and anemone relationship: The clownfish and anemones represent a model of symbiotic relationship in which both parties benefit of such relationship. In order to establish such relationship, the clownfish has to acquire an immunity to protect them against the stings of their host (anemone). The protection develops in a form of a layer of mucus or slime coating which protects the clownfish against the anemone’s lethal sting making the fish as one of a few fish that can swim freely between the poisonous tentacles of an anemone without being stung. The protective slime is a mixture between the slime of the anemone with its stinging cells and its own skin slime.
The benefits of such symbiotic relationship could summarize what benefits each party gets. The anemone provides a safe home for the clownfish where most fish other than clown fish avoid these stinging anemones. In return, the clownfish will eat the remains of fish paralyzed and eaten by the anemone. The clownfish eats the rotten or dead tentacles of the anemones and could also feed on small invertebrates that could harm the anemone.
The clownfish sticks close to their anemone host which provides them with enough protection to the predation if they move far away by large fish species such as sharks and eels).
Changing sex and reproduction: All clownfish are born male. They have the ability to switch their sex, but will do so only to become the dominant female of a group. When the female dies, the largest male in the area will take her place and becomes the breeding female. This phenomenon is known as protandrous hermaphrodites.
Female clownfish lays her eggs in hundreds or thousands depending on species. Eggs are laid on flat surfaces close to their host anemone. The male parent will usually guard the eggs until they hatch in about 6 to 10 days depending on water temperature. The male continues to take care of the hatched fry until they reach sexual maturity.
The spawning and hatching follow the lunar clock. It is believed that the nocturnal hatching during high tide may reduce predation by allowing for a greater capacity for escape.
References: Wikipedia, Gender and life, National Geographic, Shedd (The World’s Aquarium), Sea Life, a-z animals
Credit for the photos and information providing: Sherif Sadek and Mohamed Sabry (ACO)- Egypt
Reporting: Abdel Rahman El Gamal
The two photos address the stocking of nursed juveniles of about 1-g and plus of average size into an earthen pond which was prepared and cleared of unwanted fish and crabs. Grow-out ponds are well screened to ensure no entry of unwanted organisms. In this particular farm, shrimp juveniles are stocked at a density of 6 juveniles/m2. As shown in one photo, stocked juveniles are acclimatized to pond waters. Some shrimp farms lack the nursing facility, in such case, the shrimp post larvae acquired from the shrimp hatchery are stocked directly into the grow-out pond with higher stocking density to make-up the expected higher mortality rate in this case.
The farming system in the present farm adopts a polyculture system whereas a species of mullet of high market value (keeled mullet, Liza carinata) which is stocked at the rate of 2500 pieces/acre of 2-g average size.
The photos were taken by Glenda Vélez Calabria at in mundo marino and te mostramos lo que pasa en el fondo, Colombia
Scientific review: Abdel Rahman El Gamal
General: The spotted scorpionfish, Scorpaena plumieri is also known as the pacific spotted scorpionfish, stone scorpionfish, stinging groupers, and spotted stone scorpionfish. The species is used as an aquarium fish and they are also eaten in local communities where they live. The spotted scorpionfishes have separate sexes.
Description: The spotted scorpionfish is one of the largest and most common scorpionfishes species. They have elongate body with head equipped with many spines and ridges. The length of the species can range from 18 – 36 cm with males can get up to 45cm and about 1.5kg. Their fleshy plumes over their eyes, as well as their skin flaps around their head and their mottled wide-range of brown to black coloring makes lead to the effective camouflage which make them blend with the surroundings into their habitats whether reef or rocky bottoms. The species has three dark bars on their tails. This species has brilliant white spots on a black background located on the topside of the pectoral fins. These spots are only visible when the fish is disturbed. This species has pressurized venom glands at the base of its dorsal fin where the poisonous spines in their fins are used for defense through injecting the venom upon the penetration of the spines; the venom is not deadly to humans.
Geographic distribution and habitats: Scorpionfishes, Scorpaena plumieri are usually found in sub-tropical climates in the Western Atlantic from Bermuda, Massachusetts, and the northern Gulf of Mexico to southern Brazil. They are also found in the Eastern Atlantic around Ascension and St. Helena.
Scorpionfishes commonly inhabit shallow coral reeds and are mostly found at depth range of 1-60 m. They prefer hard bottoms in rocky areas. They are most commonly found lying motionless and well camouflaged on the bottom blending in with the background.
Feeding habits: The Scorpaena plumieri are predators that feed nocturnally on fish, crabs, shrimp, and octopods. Their camouflage helps them to remain motionless undetected and wait for the prey to become within their striking distance. The wide mouth of the species enables them to suck and swallow the prey. The venom which the species has is not used for catching or killing the prey. On the other hand, the scorpionfish maybe preyed upon by large snappers, sharks, rays and moray eels.
Note: Because the species may remain motionless for long periods of time, considerable loads of crustaceans and algae often live on them. The shedding of their outer layer of the skin is performed by fish in order to get rid of these parasitic organisms.
References: MARINEBIO, Marine Species Identification Portal
Credit: Sherif Sadek and Mohamed Sabry (ACO), Egypt
Reporting: Abdel Rahman El Gamal
The post larvae (PL) of the Indian white prawn (Penaeus indicus) upon purchasing from shrimp hatcheries are typically PL-15. Shrimp farms which have nursing facilities such as this farm receive the PL-15 shrimp for nursing in such polyethylene lined facility as shown in the photo. During a 30-day nursing period, the post larvae are offered specialized shrimp feed with a protein and fact contents of 34% and 15% respectively. The size of feed crumbles starts with 0.6 mm increasing as shrimp grows while ending with 2-mm diameter by the end of nursing period where the shrimp develops to juveniles of about 1.2 – 1.5 g average size. These juveniles will be suitable to be harvested and moved to grow-out ponds. The survival rate during the nursing period is estimated to be about 75%.
Credit: Sherif Sadek and Mohamed Sabry, ACO, Egypt
The photos show an important process in the preparation of an earthen pond prior to the stocking of the juveniles of Indian white prawn, Penaeus indicus. In this phase of preparation, chlorine solution of effective strength is applied to water bodies left after draining and to any suspect places which could have unwanted and/or left-over of fish or crabs which could pose series threat to the stocked shrimp juveniles. One of the photos shows the collected crabs after the chlorine treatment. This farm is located in the triangle area along Port Said/Damietta road, Egypt.
Snakes are considered a problem for some fish ponds especially the earthen and open ponds. Snakes around or inside fish ponds could be venomous or non-venomous water snakes whereas the later ones are more common. Even though, water snakes feed mainly on frogs, but they can also prey on fish. The field observations suggest that snakes may eat only small or weak fish while grown and healthy fish are not at risk due to the existence of snakes. However, growers attempt to keep snakes out of pond environment through appropriate preventative measures that has been used including:
Keeping the premises around the fish pond clearing and clean; the bushes could serve as hiding places for the snakes
Placing specific materials of sharp and unpleasant odor around the ponds could serve keeping snakes out. Examples of these substances are moth balls, sulfur, cedar oil and This herb wormwood (Artemisia absinthium)
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Video credit: Manuel Cano Alfaro (Guatemala)
Review: Manuel C. Alfaro and Abdel Rahman El Gamal
As been established long time ago, the development of tilapia aquaculture depends mainly on the use of all-male tilapia fingerlings. The all-male tilapia culture does not only target the higher growth rate of male tilapia compared to females but also eliminates the unwanted reproduction of tilapia that matures at younger age. The use of male hormone 17 alpha-testosterone has been widely used in tilapia hatcheries for producing all-male tilapia fingerlings. However, the use of hormone has raised some environmental concerns as well as health concerns to hatchery operators who could prepare the hormonal treated feed. These concerns led to the banning of hormonal use in sex reversal of tilapia in many countries. The use of super male with YY sex chromosomes in the production of all-male tilapia fingerlings is seen a safe method especially it depends on the mating of super male which has been produced somewhere else with normal females (xx) and all-male offspring (xy) are produced without any hormones. It may worth mentioning that the YY males of Nile tilapia (Oreochromis niloticus) are usually produced in specialized facilities where female hormone (estradiol) is used in the first phase of the process. However, it is always assumed that in such specialized facilities, the good management practices are enforced and so environmental and health concerns are taken care of.
The hatchery shown in this video is located belongs to the University of San Carlos de Guatemala operated by the “Centro de Estudios Marítimos y Acuicultura” (CEMA). The YY super male of Nile tilapia, Oreochromis niloticus used in the hatchery have been produced at Costa Rica. Even though the hatchery production was not published, it seems that 160,000 fingerlings/month is a good estimate. Produced fingerlings are provided to tilapia producers in the Pacific slope of Guatemala.
