Department of Aquaculture
Jack: I’m starving. Let’s go and get something to eat.
July: Okay. What do you like to have?
Jack: How about seafood? Do you like seafood?
July: Sure. I’ve heard white meat is healthier than red meat, and it is also a good source of protein in our diets.
Jack: Do you know aquaculture, that is, fish farming is popular in Taiwan?
July: Really? I thought all the seafood we eat was wild seafood that were harvested from the sea.
Jack: No, not exactly, especially when the world´s fisheries were over-exploited and wild seafood has been dramatically depleting. By the way, do you know how seafood is classified?
July: Not exactly. How is it classified?
Jack: Well, basically seafood can be either animals or edible plants. According to the ISSCAAP classification (International Standard Statistical Classification of Aquatic Animals and Plants) used by the FAO (The Food and Agriculture Organization of the United Nations), seafood can be divided into 5 groups: fish, molluscs, crustaceans, other aquatic animals, and aquatic plants and microphytes.
July: Interesting! Tell me more.
Jack: Fish are aquatic vertebrates, and they can be further divided into 4 subgroups:pelagic fish,demersal fish, diadromous fish, and freshwater fish. July: I didn’t know there were so many kinds of fish. How are they classified?
Jack: They are classified according to the place they live. For example, pelagic fish are those which live and feed near the surface or in the water column of the sea, but not on the bottom of the sea. Those that live and feed on or near the bottom of the sea are called demersal fish. Those that migrate between the sea and fresh water are diadromous fish. And of course those that live in rivers, lakes, reservoirs, and ponds are called freshwater fish.
July: Can you give me some examples of the fish in each category?
Jack: No problem. Pelagic fish can be larger predator fish like sharks, tuna, marlin, swordfish, mackerel; and smaller forage fish like herring, sardines, sprats, anchovies, and menhaden. In the demersal fish group, there are cod, flatfish, grouper and stingrays. Salmon, shad, eels and lampreys are on the other hand are diadromous fish. Common freshwater fish are carp, tilapia, catfish, bass, and trout.
July: Impressive! How about the other groups of seafood?
Jack: Molluscs are invertebrates with soft bodies. They can be further divided into subgroups of bivalves, gastropods, which are protected by a calcareous shell, and cephalopods, which are not protected by a shell. Bivalves, sometimes referred to as clams, have a protective shell in two hinged parts. Important seafood bivalves include oysters, scallops, mussels and cockles. Aquatic gastropods, also known as sea snails, are univalves which means they have a protective shell that is in a single piece. Gastropod literally means stomach-foot, because they appear to crawl on their stomachs. Common seafood groups are abalone, conch, and limpets. Unlike bivalves and gastropods, cephalopods are not protected with a shell. Cephalopod literally means head-foots, because they have limbs which appear to tissue from their head. Examples of cephalopods are octopus, squid and cuttlefish.
July: How about shrimps, my favorite kind of seafood?
Jack: Shrimps are crustaceans, another group of seafood. Like molluscs, crustaceans are invertebrates, but with segmented bodies protected by hard crusts. Shrimps, crabs, lobsters and krill are subgroups of crustaceans.
July: How about turtles?
Jack: They belong to the group of other aquatic animals, in which there are aquatic mammals, like whales and dolphins; aquatic reptiles, like turtles and crocodiles; echinoderms, which are headless invertebrates like sea cucumbers and sea urchins; and jellyfish.
July: Is seaweed a kind of seafood?
Jack: Yes, seaweed is macroscopic forms of algae and is popular in China, Japan, and Korea. In contrast, there are microscopic forms of aquatic plants called microphytes, which are microscopic organisms, and can be algal, bacterial or fungal.
July: Well, I’ve had enough of all the scientific names. Should we eat now?
在學術英文中經常使用被動式，尤其在描述研究的過程和結果或材料應用上。被動式的型態為 be + 過去分詞。
Fish are aquatic vertebrates, and they can be further divided into 4 subgroups.
– A is/are B which/that …
Fish are aquatic vertebrates which lack limbs with digits, use gills to breathe, and have heads protected by hard bone or cartilage skulls.
Aquatic gastropods, also known as sea snails, are univalves which means they have a protective shell that is in a single piece.
|conversion of feed||飼料轉換|
|efficient filling and draining of water||有效注水和排水|
July: Thanks for the dinner. It was very delicious. I wish we could always have seafood so delicious like this.
Jack: With aquaculture technology today, you can have your dream come true.
July: That’s good to know. But how is it done?
Jack: The first step for fish culture is fish propagation, which can be natural, semi-artificial or artificial. In order to secure the quantity of fry, a well-equipped hatchery is often used.
July: What is fry?
Jack: Fry is young, small fish.
July: Then, how about mature fish that produce fry? What are they called?
Jack: They are brood stock or brood fish, a group of mature individuals used in aquaculture for breeding purposes. They may be wild population, like sturgeons (Acipenseridae), mullets (Mugilidae), and salmonids
(Salmonidae), captured from rivers or lakes for their milt or eggs. After their milt or eggs are stripped, they are released back to their habitats. However, there may also be brood stock cultured in fish ponds.
July: I guess not every pond is suitable for culturing brood stock.
Jack: You’re right. There are some environmental conditions for culturing breeders, and they are: water quality and pond, temperature, oxygen, and photoperiod (day length).
July: Interesting. I’d like to know more details on each requirement.
Jack: Sure. During culturing of breeders, the water quality should meet the same
requirement of routine fish culture. In addition, for species preferring still water, for example cyprinids, catfish, and tilapia, earthen or concrete-walled fish ponds should be constructed. On the other hand, for rheophyllic species like trout, flow-through systems, canals, or tanks with circulating water should be provided.
July: How about temperature?
Jack: Similar to water, temperature plays an important role in fish culture. Fish are poikilothermic animals, whose internal temperature varies according to their surrounding temperatures. Therefore, there are warm water and cold water species of fish.
July: So, the water temperatures they need are different.
Jack: Smart. The optimal range of temperature for cold water fish, like salmonids and trout, is between 10 and 16°C and their oxygen demand is high. The optimal range of temperature for warm water fish, like common carp, Chinese carp, Indian carps; and from other families like the tilapia, milkfish, mullet and the American catfish, on the other hand, is between 18 and 26°C.
July: Fascinating. In addition to the temperature, I believe the content of oxygen in the water is very important too.
Jack: Definitely. Optimal oxygen content of water is crucial for the culture of brood stock. Because the development of gametes and the conversion of feed consume a lot of oxygen, the deficiency of oxygen would result in the slowdown of gametogenesis and even the resorption of gametes. July: Without oxygen, I guess it is hard for any animals to survive.
Jack: There’s another significant factor that needs to be taken into account and it is photoperiod, length of day.
July: Are there more factors that would affect the culture of brood stock?
Jack: Yes. In addition to the environmental factors, psychological factors such as
stress must be borne in mind during the process of handling, transportation and enclosure. Otherwise, the stress may hinder the last phase of maturation and ovulation.
July: Well, can the stress be minimized and how?
Jack: Yes. The stress can be reduced if the following conditions are met. First, control the stocking density to ensure the supply of natural food. Second, control the water supply, flow rate, temperature and oxygen content to meet the requirements of the fish. Third, during spawning because the fish must be caught very often, keep breeders in smaller size of fish ponds with efficient filling and draining of water. When being transported, breeders should be kept in tanks with proper oxygen content, and sedatives can be added to the water for timid fish like Chinese carps. Whenever handling or manual transportation is necessary, it is highly suggested that skillful
fishermen conduct the process and seine be used.
July: Of course. All the necessary precautions have to be taken to ensure the success rate of the culture of brood stock.
Fish are poikilothermic animals, whose internal temperature varies according to their surrounding temperatures.
There’s another significant factor that needs to be taken into account