Fish of the Week – Tilapia

August 13, 2013 at 9:38 AM | Posted in fish, Fish of the Week, tilapia | Leave a comment
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Fish of the Week – Tilapia

Nile tilapia, Oreochromis niloticus

Nile tilapia, Oreochromis niloticus

 

 
Tilapia (/tɨˈlɑːpiə/ ti-la-pee-ə) is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia are mainly freshwater fish, inhabiting shallow streams, ponds, rivers and lakes, and less commonly found living in brackish water. Historically, they have been of major importance in artisan fishing in Africa and the Levant, and are of increasing importance in aquaculture and aquaponics. Tilapia can become problematic invasive species in new warm-water habitats, whether deliberately or accidentally introduced, but generally not in temperate climates due to their inability to survive in cooler waters below about 21 °C (70 °F).

 

 

Tilapia were one of the three main types of fish caught in Biblical times from the Sea of Galilee. At that time were called musht, or commonly now even “St. Peter’s fish“. The name “St. Peter’s fish” comes from the story in the Gospel of Matthew about the apostle Peter catching a fish that carried a coin in its mouth, though the passage does not name the fish. While the name also applies to Zeus faber, a marine fish not found in the area, a few tilapia species (Sarotherodon galilaeus galilaeus and others) are found in the Sea of Galilee, where the author of the Gospel of Matthew accounts the event took place. These species have been the target of small-scale artisanal fisheries in the area for thousands of years.
The common name tilapia is based on the name of the cichlid genus Tilapia, which is itself a latinisation of thiape, the Tswana word for “fish”. Scottish zoologist Andrew Smith named the genus in 1840.

 

 

Tilapia typically have laterally compressed, deep bodies. Like other cichlids, their lower pharyngeal bones are fused into a single tooth-bearing structure. A complex set of muscles allows the upper and lower pharyngeal bones to be used as a second set of jaws for processing food, allowing a division of labor between the “true jaws” (mandibles) and the “pharyngeal jaws”. This means they are efficient feeders that can capture and process a wide variety of food items. Their mouths are protrusible, usually bordered with wide and often swollen lips. The jaws have conical teeth. Typically tilapia have a long dorsal fin, and a lateral line which often breaks towards the end of the dorsal fin, and starts again two or three rows of scales below.

 

 

Tilapia as a common name has been applied to various cichlids from three distinct genera: Oreochromis, Sarotherodon and Tilapia. The members of the other two genera used to belong to the genus Tilapia but have since been split off into their own genera. However, particular species within are still commonly called “tilapia” regardless of the change in their actual taxonomic nomenclature.
The delimitation of these genera among each other and to other tilapiines requires more research; mtDNA sequences are confounded because at least among the species of any one genus, there is frequent hybridization. The species remaining in Tilapia in particular still seem to be a paraphyletic assemblage.

 

 

The tilapiines of North Africa are the most important commercial cichlids. Fast-growing, tolerant of stocking density, and adaptable, tilapiine species have been introduced and farmed extensively in many parts of Asia and are increasingly common aquaculture targets elsewhere.

 

Red nile tilapia under the experiment (CLSU), Philippines)

Red nile tilapia under the experiment (CLSU), Philippines)

 

Farmed tilapia production is about 1,500,000 tonnes (1,500,000 long tons; 1,700,000 short tons) annually with an estimated value of US$1.8 billion, about equal to that of salmon and trout.
Unlike carnivorous fish, tilapia can feed on algae or any plant-based food. This reduces the cost of tilapia farming, reduces fishing pressure on prey species, avoids concentrating toxins that accumulate at higher levels of the food chain and makes tilapia the preferred “aquatic chickens” of the trade.
Because of their large size, rapid growth, and palatability, tilapiine cichlids are the focus of major farming efforts, specifically various species of Oreochromis, Sarotherodon, and Tilapia, collectively known colloquially as tilapia. Like other large fish, they are a good source of protein and popular among artisanal and commercial fisheries. Most such fisheries were originally found in Africa, but outdoor fish farms in tropical countries, such as Papua New Guinea, the Philippines, and Indonesia, are underway in freshwater lakes. In temperate zone localities, tilapiine farming operations require energy to warm the water to tropical temperatures. One method uses waste heat from factories and power stations.
China is the largest tilapia producer in the world, followed by Egypt.
In modern aquaculture, wild-type Nile tilapia are not too often seen, as the dark color of their flesh is not much desired by many customers, and because it has a bit of a reputation of being a trash fish associated with poverty. On the other hand, they are fast-growing and give good fillets; leucistic (“Red”) breeds which have lighter meat have been developed and these are very popular.
Hybrid stock is also used in aquaculture; Nile × blue tilapia hybrids are usually rather dark, but a light-colored hybrid breed known as “Rocky Mountain White” tilapia is often grown due to its very light flesh and tolerance of low temperatures.
Commercially grown tilapia are almost exclusively male. Cultivators use hormones, such as testosterone, to reverse the sex of newly spawned females. Because tilapia are prolific breeders, the presence of female tilapia results in rapidly increasing populations of small fish, rather than a stable population of harvest-size animals.
Other methods of tilapia population control are polyculture, with predators farmed alongside tilapia or hybridization with other species.

 

Redbelly tilapia, Tilapia zilli ("St. Peter's fish) served in a Tiberias restaurant

Redbelly tilapia, Tilapia zilli (“St. Peter’s fish) served in a Tiberias restaurant

 

Whole tilapia fish can be processed into skinless, boneless (Pin-Bone Out, or PBO) fillets: the yield is from 30 percent to 37 percent, depending on fillet size and final trim. The use of tilapia in the commercial food industry has led to the virtual extinction of genetically pure bloodlines. Most wild tilapia today are hybrids of several species.

Tilapia have very low levels of mercury, as they are fast-growing, lean and short-lived, with a primarily vegetarian diet, so do not accumulate mercury found in prey. Feral tilapia, however, may accumulate substantial quantities of mercury. Tilapia are low in saturated fat, calories, carbohydrates and sodium, and are a good protein source. They also contain the micronutrients phosphorus, niacin, selenium, vitamin B12 and potassium.
However, typical farm-raised tilapia (the least expensive and most popular source) have low levels of omega-3 fatty acids (the essential nutrient that is an important reason that dieticians recommend eating fish), and a relatively high proportion of omega-6. “Ratios of long-chain omega-6 to long-chain omega-3, AA to EPA, respectively, in tilapia averaged about 11:1, compared to much less than 1:1 (indicating more EPA than AA) in both salmon and trout,” reported a study published in July 2008. The report suggests the nutritional value of farm-raised tilapia may be compromised by the amount of corn included in the feed. The corn contains short-chain omega-6 fatty acids that contribute to the buildup of these materials in the fish.
The lower amounts of omega-3 and the higher ratios of omega-6 fats in US-farmed tilapia raised questions about the health benefits of consuming farmed tilapia fish. Some media reports even controversially suggested that farm-raised tilapia may be worse for the heart than eating bacon or a hamburger. This prompted the release of an open letter, signed by 16 science and health experts from around the world, that stated that both oily (i.e. high in omega-3 fatty acids) fish and lean fish like tilapia are an important part of the diet and concluded that “replacing tilapia or catfish with ‘bacon, hamburgers or doughnuts’ is absolutely not recommended.”
Multiple studies have evaluated the effects of adding flaxseed derivatives (a vegetable source of omega-3 fatty acids) to the feed of farmed tilapia. These studies have found both the more common omega-3 fatty acid found in the flax, ALA and the two types almost unique to animal sources (DHA and EPA), increased in the fish fed this diet. Guided by these findings, tilapia farming techniques could be adjusted to address the nutritional criticisms directed at the fish while retaining its advantage as an omnivore capable of feeding on economically and environmentally inexpensive vegetable protein. Adequate diets for salmon and other carnivorous fish can alternatively be formulated from protein sources such as soybean, although soy-based diets may also change in the balance between omega-6 and omega-3 fatty acids.
The US produced 1.5 million tons of tilapia in 2005, with 2.5 million projected by 2010.

 

 

Tilapia serve as a natural, biological control for most aquatic plant problems. Tilapia consume floating aquatic plants, such as duckweed watermeal (Lemna sp.), most “undesirable” submerged plants, and most forms of algae. In the United States and countries such as Thailand, they are becoming the plant control method of choice, reducing or eliminating the use of toxic chemicals and heavy metal-based algaecides.
Tilapia rarely compete with other “pond” fish for food. Instead, because they consume plants and nutrients unused by other fish species and substantially reduce oxygen-depleting detritus; adding tilapia often increases the population, size and health of other fish.
Arizona stocks tilapia in the canals that serve as the drinking water sources for the cities of Phoenix, Mesa and others. The fish help purify the water by consuming vegetation and detritus, greatly reducing purification costs.
Arkansas stocks many public ponds and lakes to help with vegetation control, favoring tilapia as a robust forage species and for anglers.
In Kenya, tilapia help control mosquitoes which carry malaria parasites. They consume mosquito larvae, which reduces the numbers of adult females, the disease’s vector.
Tilapia also provide an abundant food source for aquatic predators.

 

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