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How to manage earthen pond, hatchery and management of tampolin tanks

Prehistoric Fish Had Most Powerful Jaws(Dunkleosteus terrelli )

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Prehistoric Fish Had Most Powerful Jaws

By Robert Roy Britt November 28, 2006















A painting of an artist's impression of Dunkleosteus terrelli by Karen Carr in the Field Museum's Evolving Planet exhibit. Photo by Mark Westneat

It was big. It was mean. And it could bite a shark in two.

Scientists say Dunkleosteus terrelli [image] might have been "the first king of the beasts." The prehistoric fish was 33 feet long and weighed up to four tons. It had bladed jaws, a flesh-tearing feature that the sharks it preyed upon had not yet developed.
Now scientists have learned Dunkleosteushad the most powerful jaws of any fish ever, its bite rivaling that of T. rex and modern alligators.
The creature lived 400 million years ago.
"Dunkleosteus was able to devour anything in its environment," said study leader Philip Anderson, at the Department of Geophysical Sciences at the University of Chicago.

Fast and powerful

Scientists already knew Dunkleosteus was the dominant predator of its time.

But Anderson and Mark Westneat, Curator of Fishes at the Field Museum in Chicago, used a fossil of the creature [image] to make a computer model of its muscles and its bite. They conclude that could chomp with 1,100 pounds of force, which translates to 8,000 pounds per square inch at the tip of a fang.

And it was quick, opening its jaws in just one fiftieth of a second. That action would have created suction to draw prey into its mouth.

Fish typically have a powerful bite or a fast bite, but not both, the researchers said.
Fish vs. shark

Dunkleosteus was one of many species of placoderms, a diverse group of armored fishes that dominated aquatic ecosystems during the Devonian period.

Giant armored prehistoric fish may have fed on plankton
Likely measuring more than 5 meters (16 ft) in length, Titanichthys was a giant armored fish that swam the oceans 380 million years ago. It may sound intimidating, but new research suggests that it fed in a manner much like that of today’s harmless basking shark.
Titanichthys was a member of the placoderm species. The fossilized remains of its relatives – which included the better-known Dunkleosteus– clearly show sharp teeth and crushing plates within the mouth. This indicates that those other placoderms probably bit into large prey items, and may also have ground up animals that had hard shells.
By contrast, Titanichthys had a much narrower lower jaw, that lacked teeth or any other cutting/crushing surfaces.
Working with colleagues from the University of Zurich, scientists from the University of Bristol created a computer model of such a jaw bone, based on Titanichthys fossils found in the Moroccan part of the Sahara Desert. Utilizing a technique known as Finite Element Analysis, they then virtually subjected that model to the type of mechanical stress it would experience if biting into large or hard-shelled prey.
It was found that if used for that purpose, the jaw would likely break. The same thing was observed in jaw models from present-day whales and sharks – especially the basking shark – that practise what’s called continuous ram feeding.This means that they swim through the water with their mouth open, capturing large quantities of small organisms such as plankton.
We have found that Titanichthys was very likely to have been a suspension-feeder, showing that its lower jaw was considerably less mechanically robust than those of other placoderm species that fed on large or hard-shelled prey,” says U Bristol’s Sam Coatham, lead author of a paper on the research. “Consequently, those feeding strategies (common amongst its relatives) would probably have not been available for Titanichthys.”

Good evening once again 🏠

I have a brief advice for newbies and for us unprofessional catfish farmer

Sometimes we/ ourselves create way to learn in the hard way

Also note that all mistakes in catfish rearing is a plus in building knowledge.

You can only build knowledge with mistakes only if you claim hustle down to get proper guide from the gurus our there

If you are a newbies in any of my group that this teaching is presently on going

This is for you 👉👉👉👉👉👉👉👉👉👉👉We are presently in an unknown season ...meaning we should be in the harmattan season by now , but the weather seems changing in different part of the country

This is affecting the soil so many farmer are having issues with there seeds most especially the breeders

This are part of the signs this present season meant give 👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇
Lots of fishes will die due to cold but if you ll take precautions, you ll help them navigate all through the season without loosing your fishes most expecially the concrete and Tarpaulin ponds fish farmers🌝🌝🌝🌝🌝🌝🌝🌝🌝🌝🌝🌝🌝🌝

continuation of our last studies
Fish-Poultry culture: In this type poultry farm is constructed over a platform built of bamboo sticks above the water level of the pond. This facilitates direct fertilization of the pond by droppings of chick which are rich in nitrogen and phosphorus.

Rice - Fish culture: Fish are cultured in rice fields in this method. Fishes which can live in a depth of 15cm are selected for this culture. The rice variety selected for this purpose should also develop strong root system.

Fish culture in pokkali fields: This practice is followed in kerala. Prawn, fish and rice are cultured on rotational basis in the pokkali rice fields which are influenced by tides of vembanad backwaters. Rice cultivation is taken up from June to September. Fish and prawn are cultured upto May.

Coconut or Banana - Fish Cuture: In banana or coconut fields, the ditches or canals in between the rows of plants can be utilised for fish culture in this method. These canals are always filled with water and rich In insect population.

4. Lacustrine Fisheries

The culture of fish in takes constitute lacustrine fisheries. Natural lakes of 0.72 million hectares and manmade lakes of 65 million hectares are available for fish culture in India.

5. Sewage Fisheries


In many countries fishes are introduced and cultured on commercial basis in sewage canals and ponds. The sewage is used as fertilizer in culture ponds and as feed for fish.

FISH CULTURE AND REARING METHODS

1. Composite Fish Culture

Maximum exploitation of the aquatic resources through the introduction of selected varieties of compatible fish to achieve high productivity is called composite fish culture or polyculture.
Composite fish culture has been in practice in India since ancient times. The combined efforts of Central Inland Fisheries Research Institute (CIFRI) and Indian Council of Agricultural Research (ICAR) propose the following ratios of different fishes for high yielding in polyculture.
Grass carp, silver carp, scale carp and mirror carp in the ratio of 5: 3 : 8 : 2.

Grass carp, silver carp, rohu, scare carp and mirror carp in the ratio of 5 : 3 6 8 : 2.

Grass carp, silver carp, catia, rohu, scale fish and mirror carp in the ratio of 5: 3 3 : 6 8 : 2.

2. Cage Culture
In cage culture the fishes are reared in a cage made of Nylon and wooden frame and some times in a cage made up of bamboo mesh. These cages are kept in flowing waste water canals. By this method the fishes can be protected from predators and number of fishes can be culture. Fishes feed upon the food available in waste waters. The waste waters can be re utilised for irrigation. The complications in management and investment are very little in this type of culture.
3. Integrated Fish Culture
Culturing of fish in association with agriculture or ducks or chicks or pigs or prawns is called Integrated fish culture.Fish wastes fertilize the crop fields while wastes from crops and poultry chicks are used as feed by fish. individually these farming methods may yield low income. But integrated farming technique yields multiple products of nutritional value and economic importance. Various types of integrated fish culture methods are in practice today. They are Fish-Prawn culture: Prawn are cultured in ponds which are meant for carp culture in this method. The excreta of carp fishes constitute food for prawns.

HATCHERY PRODUCTION PROCEDURES

3.1- BROODSTOCK MANAGEMENT

Establishing the broodstock

To work properly and with adequate safety margins, any hatchery should secure a reliable and sufficient supply of good quality fish eggs. With this aim in mind, most Mediterranean hatcheries have established their own broodstock units, where breeders of different age groups of the species involved are kept under long term stocking conditions.

However, timing, amount and quality of the eggs produced by these units do not always fit hatchery requirements, resulting sometimes in poor final outputs in terms of viable fry.

The importance of a properly dimensioned and managed broodstock unit is now fully acknowledged and its relatively high running costs are fully justified.

In the management of a fish broodstock unit the main issues to be considered refer essentially to:

stock dimensioning;

stock collection;

adaptation to captivity and long-term stocking conditions;

sexual maturation and spawning according to the production schedule;

renewal of the old breeders.

Stock dimensioning

To properly determine the dimension of the broodstock unit, different parameters have to be taken into consideration. First, the seasonal production target for the hatchery has to be set. In particular the desired number of fry, their size and species and delivery timing should be planned. To this purpose, it is important to set the average survival rate from larva to weaned fry. Second, the reproductive characteristics of the species, such as sexual cycle pattern, egg productivity and latency period (see Table 3.1) play a key role in stock dimensioning. A third important aspect is represented by the possibility to introduce a year-round supply of eggs, which requires the manipulation of photoperiod and temperature to obtain out-of-season maturation and spawning.

As described in Part 2 of the manual, both seabass and gilthead seabream are seasonal breeders spawning in winter and early spring.

Today, fish provides more than one billion poor people with most of their daily animal protein. Fish provides nutrients and micronutrients that are essential to cognitive and physical development, especially in children, and are an important part of a healthy diet. As an affordable animal source of protein in some of the poorest countries, fish is the primary source of nutrition, creating growing demand for this staple. However, fish supplies are failing to meet demand and there are major shortages in some critically poor countries where they are needed most.

Globally, more than 250 million people depend directly on fisheries and aquaculture for their livelihoods and millions are employed in fisheries and aquaculture value chains in roles such as processing or marketing. The very poor often rely on fishing as a primary source of income. These small-scale fishers are particularly vulnerable as fish stocks diminish. Increased productivity from sustainable fisheries and aquaculture can be a driver for rural development by mitigating risks to livelihoods and contributing to income generation and employment.
mproving the productivity of fisheries and aquaculture is vital to reducing hunger and poverty for millions in the developing world. Sustainable, productive fisheries and aquaculture improve food and nutrition security, increase income and improve livelihoods, promote economic growth and protect our environment and natural resources.

A sustainable approach to fisheries and aquaculture will help to protect our natural resources and ensure that fish stocks are available for future generations. Currently, overfishing, ineffective management practices, industrial development and agricultural pollution have reduced fish stocks. While sustainable fisheries management is a challenge, solid global and regional governance of these vital resources will ensure that we can produce enough fish for those living in poor regions.

The red lionfish is an ambush predator. It moves very slowly and often sits perfectly still, waiting for small fishes to approach too closely, at which point it lunges aggressively toward its prey. At the same time, it extends its jaws forward, creating a large amount of suction, and easily swallowing the prey whole. This species is not a picky eater and will eat just about any fish that it can swallow, limited only by the size of its mouth. As it grows larger, the size of the prey that it can attack and eat also grows larger. Some individuals have been observed slowly cornering prey with their large fins before attacking. In its natural geographic range, the red lionfish is eaten by large bony fishes and coastal sharks. In the western Atlantic, it has few (if any) natural predators. In both basins, it uses its venom-filled spines in an attempt to guard against predation (not to attack prey).
Male red lionfish are somewhat territorial and court females that enter the part of the reef that they defend. After successful courtship, a male-female pair reproduces by a behavior known as broadcast spawning. In this method, the female releases her eggs and the male releases his s***m in the water column, above the reef, at the same time. This behavior increases the likelihood that eggs will become fertilized and decreases the likelihood that fertilized eggs will be eaten by egg predators at the reef surface.
Red lionfish are eaten in some places but are not targeted heavily for human consumption. In the past, they have been captured alive, in large numbers, for display in public and private aquaria. They are naturally rare and have likely been depleted in some areas, but a more serious consequence of their live capture is the accidental establishment of large populations outside of their normal range. In the 1990s, one or several individuals were released by pet owners in Florida, USA, and over the course of the past twenty years, the red lionfish has become a very common,.

The puffer, which is also called swellfish, or blowfish, is any member of a group of about 90 species of fishes of the family Tetraodontidae, noted for their ability when disturbed to inflate themselves so greatly with air and water that they become globular in form. Puffers are found in warm and temperate regions around the world, primarily in the sea but also, in some instances, in brackish or fresh water. They have tough, usually prickly skins and fused teeth that form a beaklike structure with a split in the center of each jaw. The largest puffers grow about 90 cm (3 feet) long but most are considerably smaller.
Many species are poisonous; a highly toxic substance, tetraodontoxin, is especially concentrated in the internal organs. Although this substance can cause death, puffers are sometimes used as food. In Japan, where the fishes are called fugu , they must be carefully cleaned and prepared by a specially trained chef.
Lionfishes (Pterois) make up any of several species of showy Indo-Pacific fishes of the scorpion fish family, Scorpaenidae (order Scorpaeniformes). They are noted for their venomous fin spines, which are capable of producing painful, though rarely fatal, puncture wounds. The fishes have enlarged pectoral fins and elongated dorsal fin spines, and each species bears a particular pattern of bold, zebralike stripes. When disturbed, the fish spread and display their fins and, if further pressed, will present and attack with the dorsal spines. One of the best-known species is the red lionfish ( Pterois volitans ), an impressive fish sometimes kept by fish fanciers. It is striped with red, brown, and white and grows to about 30 cm (12 inches) long. The red lionfish is native to South Pacific reef ecosystems. In the early 21st century the species became established in reef ecosystems along the Eastern Seaboard of the United States,in the Gulf of Mexico, and in the Caribbean Sea. Its rapid rate of reproduction, combined with the absence of natural enemy

Managing Systems for Tilapia Culture
Definition
Tilapias ( Oreochromis spp .) are increasing in popularity with consumers, and a number of fish producers in the United States are culturing them. During winter months in Alabama, surface water temperature falls too low for tilapia survival. Broodstock may be overwintered in waters heated by geothermal, solar, or mechanical means with spawning, nursery, and grow-out conducted during warm months. Alternatively, indoor culture systems with heating allow year-round culture, but energy for heating increases production costs.
Tilapia may be produced in tanks, raceways, cages, or open ponds. Although they are efficient filter feeders and use plankton for food, commercial feed is applied to increase production to profitable levels. Tilapia tolerate low dissolved oxygen and high ammonia concentrations better than most aquaculture species. Thus, they are stocked at high density, resulting in waters and effluents of culture units having high concentrations of nutrients, organic matter, and suspended solids.
Explanation
Because of the necessity to provide supplemental heat to overwinter broodstock or to extend the grow-out period, water reuse systems are popular in temperate areas. Ground water in Alabama usually is warm enough to permit tilapia survival in winter. Thus, broodstock can be overwintered in tanks through which well water is passed. Placing tanks under transparent plastic covers can lessen the volume of ground water that must be applied to fish holding units. In warm months, the same units can be used to produce marketable-sized fish under more intensive conditions.
Because fish are stocked at high density in culture units, a large input of feed is necessary.

Group: Freshwater
Size: Large
Temperament: Non-aggressive
Aquarium Size: Large (50+ gal )
Swimming Region(s): Bottom
Suitable Tank Mates: Other species of catfish, Koi, Giant Gourami, Oscars, Pacu.
Catfish General Description
Catfish are a large family of freshwater fish extremely popular in the aquarium trade. Most species of catfish are extremely hardy and make for fascinating aquarium specimens. They are characterized by their whisker-like barbells which are used to gather a great deal of sensory information. Unlike most other species of freshwater fish, the catfish’s body is not covered in scales. Instead, they have thick, leathery skins which are often covered in a thin layer of mucus. Most species of catfish also have a bony and spine-like ray on their dorsal and pectoral fins. When feeling threatened, they will often lock these rays in place, making them stick outwards and providing the catfish with a certain degree of physical protection.
Origins
Different species are found in freshwater habitats across the world.
Color
The many different species come colored in shades of white, pink, brown, yellow, grey and black.
Maintenance and care
The specific aquarium needs of different species of catfish vary based on their natural habitats. However, most species are extremely hardy and can adapt to a fairly wide range of water conditions. That said, they can be sensitive to abrupt changes in water quality and are sometimes sensitive to the side effects of various medications.
Feeding
Most species are omnivores and can be fed on a pellet or algae disk based diet. Some species, like plecos, are scavengers and will scour the aquarium bottom and sides for algae. Some carnivorous species may also devour smaller tank mates that they can fit in their mouths.
Breeding
It is virtually unheard of for catfish to breed in the home aquarium.
Aquarium varieties
Otocinclus, Cory, Pleco, Bristle Nosed, Clown, Iridescent Shark, Glass, Bumblebee, Columbian Shark, etc.

QUICK STUFF (source: California DFG and Peterson Guide)
Basically there are four different kinds of catfish in the Delta:
Of these, you are more likely to catch white and yellow catfish. In fact, the DFG says that 95% of catfish caught in California are white catfish. Could be, but for me it's always been a 50/50 split between whites and yellows, probably because I'm more apt to fish in their habitat: shallow, brackish, muddier waterways like small sloughs and back channels. Best areas I've found for them are Grizzly Island and Hill or Montezuma sloughs, Sherman Island on the San Joaquin River side; and the Whiskey Slough/Empire Cut area. Brown catfish like deep, slow moving waters with gravel and mud mixed bottoms. Central Delta, around the Franks Tract region, is a good example. Channel cats, the largest catfish in the Delta, prefer deep swift water with mostly gravel bottoms. The deep water shipping channels of the Sacramento/ San Joaquin river system are top choices.
An observation: if you are looking for the big channel catfish, you should know in advance that this is slow, patient fishing, best at night during the summertime. Channel cats are meat-eaters, so don't bother with clams. If you want to catch fish quickly, however, whites and yellows are the way to go. And you can catch them year around. In fact, I'd rather go after catfish in the wintertime, when the temperatures are less searing and the crowds are thin. I even think the fish taste better in the winter and spring.

Pig farming is not only a profitable business but also a very popular and lucrative business. Pig is widely used to eat and pork. But it is not an easy tusk to farming. It takes a lot of time and money to make a profitable pig farm. To make a perfect pig farm everybody needs to follow some methods, which are described below.
Pig Farming On Pasture
Firstly, it is very necessary to have a large area with a lot of grass and soil. Then it also needs a large fence so that the pigs can roam too far off easily and can feel comfort. But the farmers should always conscious about the structure of the fence. Farmers should use very strong wood and thick corner poles because the adult pigs become very strong and they can try to destroy the fence. As pigs are notorious diggers, farmers should dig deeply into the ground for poles. Thus farmers can farm pigs on the pasture.
On a Barn or Hut
Pig farming in a barn is generally easy. Farmers should use concrete to make a barn for pig farming. It is very necessary to keep the pigs inside the farm. Farmers should make the floor slope so that the water can be used to clean the barn easily. Farmers should separate the feeding area to the rest area for cleaning it easily. At least 10 feet deep and 10 feet wide area is perfect for every two pigs. The rest area should be half the size of the feeding area with a pool where they can bath and the pool should be at least 5 feet.
You should take care the pigs in the barn in the following ways
Depending on number of pigs farmers should clean pens naturally twice in a week.
It is very important to keep feeder full.
Mud hole filled with water in outside pen.
A lot of bedding is necessary in corner but not entire pen.
Selecting Pig Breeds
There are numerous pig breeds available throughout the world. You can choose the local breeds first which are easily available in your area. Some common and popular pig breeds are;
Yorkshire , Spotted , Poland China, Landrace,
Hampshire , Duroc, Chester White.

What Is the Difference Between Farmed and Wild Fish?
One of the best things about eating seafood—besides the rich flavors, easy prep, great protein, and low calories, of course—is the variety of available options. I mean, chicken is chicken. Steak is steak. But the word “seafood” can mean a virtual cornucopia of options: saltwater fish , freshwater fish ,
crustaceans , mollusks . The choices are virtually endless!
However, regardless of whether you’re standing at the grocery store’s fish counter or staring at a restaurant menu, you’re more likely to see information nowadays about where and how your seafood was caught. And you might wonder: Does it matter? Should I care if my
salmon was from the Atlantic or Pacific? Does “responsibly farmed” mean something important? And hey—how exactly do you farm a fish, anyway? The questions could leave you scratching your head for hours.
The best and easiest way to keep track of the dizzying factors is to cheat. Resources like the
Marine Stewardship Council and The Monterey Bay Aquarium’s Seafood Watch Program are designed to help help consumers make informed choices. The Monterey Bay Aquarium even offers a handy Seafood Watch Guide app for your phone. It’s an easy-to-navigate app that uses simple color coding (green, yellow, red) to tell you whether the exact type of shrimp, tuna, or whatever you want to buy is a good, okay, or bad choice. For me, it’s been as an important a tool as my actual shopping list. However, if you want to understand more about why tools like the Seafood Watch Guide are necessary in the first place, keep reading. Here, I’ve got your handy guide to understanding and navigating some of the differences between farmed and wild seafood in a way that will make your body, your conscience, and the environment (yes, the environment) smile with contentment.

A Bountiful Harvest Still Depends On the Sea
While farmed fish and shellfish can supplement our seafood supply, they can't replace the variety and abundance of seafood from the wild. Some fish farms still depend on wild populations to supply eggs or juveniles that the farmers raise for market. Many fish farms also depend on wild fish, like sardines or anchovies, as food for the farmed species.
Some Fish Are Carnivores
Every year, millions of tons of wild fish, like sardines and anchovies, are caught and processed into fishmeal and fish oil, which is used to make feed for farm-raised species. Some of these species, like salmon—one of the most popular farmed fish in the world—require over a pound of wild fish for every pound of weight they gain. Tuna requires over 15 pounds of feed for every pound it gains.
Developing Alternative Diets
There's good news: not all fish are carnivores. Some, like catfish and tilapia, can be raised on diets with very little or no fishmeal or fish oil. Shellfish (like mussels and oysters) are another good option. These animals feed by filtering plankton out of the water and need no supplemental food.
Ranching Wild Fish
Some fish farms operate as "ranches.” Instead of raising fish from eggs, they take large numbers of fish from the wild and grow them for eventual sale. Not only do these farms still rely on wild populations, in some cases the fish they take are still juveniles. For example, young eels are caught and then farmed to supply unagi to sushi bars. Similarly, young bluefin tuna are ranched for highly-profitable but resource-intensive industry. This practice has contributed to the depletion of wild stocks of both of these species.

What is The Most Profitable Fish to Farm?
If you’re new in the fish business, you probably want to know which of the species of fish is most profitable in Nigeria, especially if you’re aware that there are hundreds of species of fish (sea trout, cyprinids, pangas catfish, freshwater fishes, silver seabream, common carp, catla, greasy grouper, bighead carp, Nile tilapia, grass carp and thousands others).
Well, the straight answer to your question is; Catfish and Tilapia and the reason is very simple__ because of our climate, their growth and the fish market.
Climate ; Just as it’s in Livestock , crops or other Agriculture business, climate and geographical locations affect different plants, species or crops differently.
Just as you may not be able to plant Apple or rear certain Goats in certain places, not all the species of fish you can rear in Nigeria.
Fish Growth; If you’re thinking of how to start a fish farming business in Nigeria, you are probably thinking of going into fish production for a commercial purpose.
What then happens when you have to rear your fish for 2 years before they weigh 1 KG?
No serious fish farmer can endure that so it’s always advisable you choose a specie that will grow fast, to meet your business plan.
Fish Market in Nigeria; Even when all the above points are in your favour, you still don’t have a business, until the market smile at what you’re selling.
After spending about decades in the business world, I can tell you that it doesn’t matter how great what you’re selling is, if the market doesn’t want it, you’ve got no business.
There are so many fishes Nigerians won’t eat (and it doesn’t matter how big they are).
What I can tell you is that, Catfish has a very large market (probably more than 70% of the entire locally produced fishes in Nigeria) and Tilapia too is loved by some Nigerians (maybe about 10% of the Nigerian fish market share).

Fish farming is an act of rearing fish for commercial purpose. This involves building the earthen, tarpaulin or concrete pond, fertilizing the pond, stocking the fingerlings in good water and feeding the Mackerel, Tilapia or catfish till market size.
While there are thousands of fish species all around the globe, only very few of them are viable for commercial fish farming.
Introduction to Fish Farming
Fish farming is known as pisciculture, that is, the breeding, rearing, and transplantation of fish by artificial means.
While fish naturally lives inside rivers, pisciculture is the means by which we grow fish at home, mostly for commercial purposes.
Fish farming is the major form of aquaculture (farming of aquatic organisms like fish, crustaceans, molluscs and aquatic plants).
Fish farming involves raising fish commercially in ponds, tanks or enclosures.
There are hundreds of species of fish, among which are; sea trout, cyprinids, pangas catfish, freshwater fishes, silver seabream, common carp, catla, greasy grouper, bighead carp, Nile tilapia, grass carp (who knows, maybe there are thousands more?).
However, most of the species of fish are not suitable for fish farming business in Nigeria, either because of their nature or because of the low demand in the fish market or the profitability of their species.
That’s why the most common fish species fish farmers grow for commercial purpose are carp, salmon, tilapia and catfish (while the last two,
catfish and tilapia is the most common species in Nigeria fish market).
Means of Growing Fish
Fish could be grown in two ways:
Extensive aquaculture where fish grow under natural water (i.e. river or stream).
Then, intensive aquaculture where fish are fed with external food supply.
Intensive aquaculture is the area we’re focusing on in this tutorial because it’s easier for commercial fish farming in Nigeria.