Culturing Finfish

KEY CONCEPTS Finfishaccount for 50%of globalaquaculture productioti. In theUnited States, finfish accounts for 74%of total aquacultureproduction. In orderto successfullyculture finfish, we musthave a goodunderstanding of the biology, ecology, anatomy, and life cycleof thespecies in question. Catfishare, by far,the most commonly cultured fish in theUnited States 7%!, Thesewarmwater speciesare cultured in freshwaterponds in southernareas of thecountry. In cool,northern waters, themost commonly cultured finfish are salmonids trout and salmon!. Currently in Maine,salmon, steelheadtrout and char are the only finfish cultured for commercial sale. However, many aquac- ulturists are learning how to commerciallygrow other fish suchas cod, haddockand flounder.

LESSON OVERVIK% Studentswill learnabout culturing finfish in Maine. They will learnhow to use a dichotomouskey to identifyseveral fish foundin Maine.By countinggrowth rings on scales,students will deter- minethe age of fish.Students will becomefamiliar with the external and internal anatomy of a bony fish through dissection.

LEARNING OB JECTIVES Af'ter completingthis chapter,the studentwill be able to: ~List the major finfish cultured in Maine. ~Distinguish between jawless fish, cartilaginousfish, and bony fish. ~ Describe how fish are classified. ~Describe the basic physiologyof the fish. ~ Describethe life history of the Atlantic salmon. ~Determine the ageof a fish by examiningscales. ~ Identify the internal and external structure of finfish. ~ Determine the function of various internal and external features of finfish. ~Demonstrate effective useof a microscope. ~ Demonstrate dissection skills.

LEARNING RESETS KEYING OUT FISH A. Classifying Life Forms: Studentswill understandthat there are similarities within the diver- sity of all living things. 2. Describesimilarities anddifferences among organisins within eachtaxonomic level, J. Inquiry and Problem Solving 1. Make accurateobservations using appropriatetools arid units of measure. AGING FISH J. Inquiry andProblein Solving: Students will applyinquiry and problem solving approaches in science and technology, l. Make accurateobservations using appropriatetools and units of measure. 2. Verify, evaluate,and useresults in a purposefulway.

87 BONY FISH DISSECTION J. Inquiryand Problem Solving 1.Make accurate observations using appropriate tools and units of measure. 2. Verify,evaluate, and use results in a purposefulway. K. Scientific Reasoning 3. Develop generalizationsbased on observations.

MATERIALS Photocopiesofthe following student handouts: Culturing Finfish in Maine, Key Out These Fish, BonyFish Dissection, Bony Fish Dissection Diagram, Gill Diagrams,Scale Types and Groivth Rings,Generalized Bony Fish External Anatomy; hand lens or dissectmg microscope, compound microscopeslides, coverslips, various species offish and scales provided byteacher, metric ru1er, projector,microprojector orslide projector, plastic sheeting, empty slide, newspaper ortable cov- eringmaterial, disposable latex/rubber gloves, tweezers/forceps, scissors, scalpel, eye dropper/ pipette,commercial quick blood smearstain, alcohol or bunsonburner.

BACKGROUND CEassification Fishare divided into threegroups: 1. Jawlessfish Agnatha! e.g.,hagfish and lampreys! 2. Cartilaginousfish Chondrichthyes! e.g., sharks, skates, rays, and chimeras! 3. Bonyfish Osteichthyes! e.g., lobe-Armed fish, lungfish, and ray-finned fish!

Forthe purpose of aquaculture,we are primarily concerned with the bony fish, and inore specifically,the ray-finned fish. There are over 20,000 species of ray-finnedfish, an extremely diversegroup found in fresh,salt and brackish waters. Most ray-finned fish, such as salmon, trout andcarp, have protective scales covering their skin. Catfish, however, do not. All ray-finnedfish havegiHs which are used to remove oxygen from the water and release carbon dioxide. The gills areusually covered by a plate-likestructure called the operculum. Fishproduce mucous through their skin which makes them feel slimy and serves a variety of functions.It allowsthe fish to movesmoothly and quickly through the water by reducing friction,it helpsmake the skin waterproof,and it protectsthe fish from bacteriaand other small organisms which can cause infections. All bonyfish have fins, although the number, shape, and purpose of thosefins vary greatly. Fishare equipped with teeth which help them catch their prey, but they don't use them for chew- ing;they must gulp their food down whole. Fish are cold-blooded which means their body re- mainsthe same temperature astheir surroundings. The bony or ray-finnedfish are an extremely diversegroup made up of manydifferent shapes, sizes, and colors. Femalefish lay eggs,which are fertilizedwith spermfroin the males.Some fish build "nests"along the bottom which they "guard" unti1 the eggs hatch. A fewfish, including some tiiapia,guard their eggs in theirmouth; they are called mouth brooders. Fish may lay thousands of eggs,but usually only otic out of 100survives to becomean adult fish. Most eggs and young are eatenby otheraquatic animals, thus contributing to thefood chain. When fish hatch,they are equippedwith a yolksac which provides thein with nourishmentfor thefirst coupleof days,after which time the yolk sac becomes absorbed and fish must fend for themselves. Physiologyof thefish the studyof bodyfunctions! All animalshave iiine body systems: 1.Skeletal 2. Muscular3. Digestive4 Excretory5. Respiratory 6, Circulatory7. Nervous 8. Sensory 9. Reproductive

In aquaticanimals, such as fish, these systems are adapted to a waterenvironment.

1.Skeletal: Fish have an internal or endoskeletonwhich provides shape, support, and protection for internal organsand muscleswhich attachto the skeleton.

2.Muscular: By contractingand releasing muscles, fish can move through the water locomo- tion!, capturefood, pass water over their gills for oxygen,and eliminate waste.

3. DigestiveSystem: Digestion is a processwhich converts food into a usableform for growth, maintenance,and reproduction. A fish's digestive system differs depending on whether it is an herbivore,carnivore, or omnivore.The digestive system usually consists of a mouth,esopha- gus, stomach, intestines, and anus.

4.Excretory System: The excretory system eliminates waste from the body and usually consists of the gills, kidneys,urinary ducts,bladder, and opening.

5. RespiratorySystem. 'Gills arethe respiratory organs of thefish. Water is pumpedover the gills anddissolved oxygen present in thewater diffuses iiito theblood stream. This oxygen is deliv- ered to the tissuesand cells of the body and exchangedfor carbondioxid, which is then ex- pelled as a wasteproduct throughthe gills and into the water.

6. Cireelatory System: The circulatory systemincludes the heart, veins, and arteriesand is re- sponsiblefor circulating blood throughoutthe body.Oxygenated blood travels to the cells and tissueswhere it is exchangedfor carbondioxide. This de-oxygenatedblood travels back to the gills, is releasedinto the water,and is replacedwith oxygen.

7.Nervous System: The fish's nervous system consists of a well-developedbrain, spinal column, nervefibers and sensory receptors. Through electrical-chemical impulses, the nervous system supplies the fish with information about its internal and external environment.

S.Sensory System: The sensory system relays information through the nervous system using the fivesenses: sight, smell, touch, taste, and hearing. The lateral line is anexternal sensory organ whichruns down the length of thefish and helps it maintainbalance and position in thewater. Somefish, like catfish,have barbels which help them feel aroundthe bottom for food.

9. ReproductiveSystem: Fish reproduce sexually to createoffspring. Males have testes which producesperm and females have ovaries which produce eggs, STUDENT HANDOUT CulturingFinfish in Maine

Culturing Salmon and Steelhead Trout Themost popular fish to culture inthe Gulf of Maine isthe Atlantic salmon. Maine aquac- ulturistshave been raising salmon since the 1970s, Hatcheries throughout thestate produce 3.5 millionfish each year for net-pensalmon farming operations along the coast. Whileprivate industry continues tofarm Atlantic salmon for profit, there are also pubIic hatcheryprograms aimed at restocking Maine's rivers and streams. Native salmon populations havebeen indecline for some time. Since there isconcern that the Atlantic salmon may disappear fromMaine's rivers completely, thefederal and state government hasbeen trying to protect the salmonthrough stricter fishing regulations, improvement orrestoration of salmon river habitat, andhatchery stocking programs. TheAtlantic salmon is ananadromous species which means they are born in freshwater, spendmost of theirlife at sea, and return to freshwater to spawn or produce young, In thewild, mostof an adult salmon's life is spent in theocean. During the spring of the fourth or fifth year, the adultfish will returnto theriver where it wasborn in orderto spawn.

Life Cycle of the Atlantic Salmon Insalmon and steelhead farms, some adult fish are kept for broodstock. These fish supply theeggs and the sperm to produceall thehatchery fish Spawningoccurs between mid-November andmid-December. A 12-pound female fish produces an average of 10,000eggs each season. Theseeggs are collected and fertiiized with sperm from the males by mixing the two together. Thefertilized eggs are then incubated ata freshwaterhatchery. The eggs hatch and eventually developinto free-swimming fry. Afterthe yolk sacis absorbed,the fish begin to eatfood on their own. Duringthe first year of life,fish develop vertical stripes on their sides. They are now calledparr. For the first 18 months of theirlife cycle in the hatchery, parr are graded, vaccinated againstdiseases, and their health and growth is monitored.After two to threeyears in freshwater, youngsalmon undergo major changes that enable them to live in saltwater. Their kidneys adapt to excretesalt, rather than retain it, andtheir skinbecomes silvery so thefish will be lessvisible to predatorsin theocean. Changes also occur in theeyes, blood plasma, musculature, and fat. This wholeprocess is called smoltijica6on. The smoIts, roughly five inches long, are transferred to floatingpens in thesea, typically between mid-April and mid-May. Thesteelhead trout, also called the sea run rainbow trout, belongs to thesame family the sahnoiuds! as the Atlantic salmon.The steelheadhas been referred to as the saltwaterversion of therainbow trout. The life cycleof the steelheadis essentiallythe sameas the Atlantic salmon, exceptthat the steelhead does not go through true smoltification. In thewild, bothAtlantic salmon andsteelhead trout returnto freshwater to spawn The steelheadlooks similarto the Atlantic salmon,but usually has an iridescentsheen; hence the name "rainbow." This rainbow sheenbe- comesbrighter when the steelhead returns to freshwater to spawn.

SabnonFarming Youngsalmon are raised in freshwaterhatcheries. When they undergo smoltification, they arethen transferred to saltwater salmon farms. In thesegrow-out facilities, salmon are housed in netpens which are generally 20 feet deep. These large pen systems, held in placewith moorings, maycover several acres of surfacewater, In thepens, fish are fed pellets of fishmeal, vitamins, andminerals. To preventthe spread of disease,fish areinoculated or antibioticsadded to thefish feed.After about two years in thepens, fish grow from smolts weighing 3 to5 ounces 80-120 grams!ta fish with a marketweight of 6 to 12pounds. A fanningoperation with 2-1/2acres of net penscan produce about 50,000 fish each year for market. When the fish reach an appropriate size, they are harvested,cleaned, and shippedto wholesaleand retail markets. Eightcommercial freshwater hatcheries in Maine produced about 3 millionyoung salmon and100,000 steelhead in 1995. There are 30 saltwater grow-out sites, located primarily in Wash- ingtonand Hancock counties, where excellent water quality, protected bays, water temperatures of0 to15'C 32-59'F!,strong currents, and high tides provide ideal conditions for raising salmon. In 1995,fish farminggenerated more than $53 million in grosssales revenue, and the salmonid aquacultureindustxy has brought much needed aid to economicallydepressed communities. In- creasingly,fishermen who depend onwild fish stocks for their livelihood are considering putting their skills to work in aquacultureto supplementtheir incomes. Anothereconomic benefit of salmonand steelhead trout farmingis the increasein the numberof family-ownedsmoke houses, where the fish are processed for a gourmetmarket. Fur- thermore,a health-consciouspublic creates a demandfor salmonand steelhead, which are excel- lentsources of protein, omega-3 fatty acids, and vitamins A, 8, D, andE. These fish species are alsolow in sodium,rich in potassium,and are natural sources of selenium,iodine, and fluorine. Salmonfarming depends on, and demands, a clean environment. One of thelargest dan- gersto salmonfarming is industrial and municipal wastewhich entersthe marineenvironment. Thispollution inay contain hazardous chemicals, heavy metals, and untreated sewage which then makeeating fish or shellfishhazardous to humans. In orderto protectthe salmon farms, pollution inputsfrom industrial or municipalsources must be very carefully monitored and regulated, Pro- tectingthe salmon pens from pollution, can help protect the marine environment as a whole.

Culturing Other Fbigsh in Maine Withthe decline in wildgroundfish populations, there is considerableinterest in develop- ing efficient techniquesfor raising cod, halibut, and haddock on fish farms. Researchersat the Universityof Mainerecently began studying both the nutritional needs of larvalcod and haddock, andthe type of foodto maximize healthy growth in theearly stages of thesefish. Atlantic Aquafarms in Franklinand the Maine Hatchety Technology Association on Swan's Island are experimenting with different ways of hatchingand raising cod and haddockon a commercialscale. Some of the youngfish will beused for restoringthe natural groundfish populations in thewaters offshore; the restwill beraised in pensuntil they are market size. Both projects are good examples of coopera- tion betweenaquaculturists and traditional fishermen. High in demand,low in supply,halibut Hippoglossushippoglossus! could be a goodcan- didatefor aquaculture.Halibut is moreresistant to stiperchillthan salmon. Maine aquaculturists havesuccessfully captured young halibut andare rearing them for future broodstockfor the Maine aquaculture industry. Halibut which can achieve a weightof morethan 100 pounds in thewild! present special challengesfor penculture. As anexperiment, young fish that weighed from seven to 10pounds werecaught by longlinefishermen and donated to thebroodstock project. Raised in pens,these fishgrew three times faster in captivitythan in nature.Now researchers are testing new "Malloch- style"cages, inade of tightlydrawn nylon mesh, and designed by growersat theMarine Technol- ogyCenter in Eastport.By the fall of 1996,27 fish were held at Maine Salmon Company's Shackford

91 Headlease site in Eastport while researchers waited for thetn to mature. Scientists expect tostudy broodstockmanagement, experiment with halibut egg incubation, and continue to investigatethe growth patternsand larval feedinghabits of halibut.

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93 ACTIVITY 1: KEYING OUT FISH

Infortnation A fish key is a seriesof questionsor statementsthat may be askedabout the characteristics of a fish.If youdo not knowthe scientific name genus and species! of a fish,you can observe the fish andanswer the questions in thekey to find thescientific name. At theend of eachquestion that pertainsto yourparticular fish is a numberdirecting you to thenext question. When you have answeredenough questions, you eventuallyfind the scientific naine of your fish.

Procedure Choosea fishand carefully answer each question, proceeding through the key. If a questionis answeredincorrectly, you will notobtain the correct scientific name. A keyis providedand may be copied and handed out to your class.

Answers to Key These Fish Handout 1! smelt 2! haddock 3! Americaneel 4! winter flounder 5! oceansunfish 6! white hake 7! hammerheadshark 8! wolffish 9! sealamprey 10! Atlantic halibut 11!alewife 12!bluefin tuna 13! Ainerican pollock 14! spiny dogfish 15! Atlantic cod 16! Atlantic mackerel FISH KEY

Sample answers for hammerhead shark

a. Doesthe fish have a bodylike a snake?2 no! b. Doesthe fish not havea bodylike a snake?3 yes! 2. a. Doesthe fish havea jaw?Anguilla rostrata Americaneel! b. Doesthe fish not havea jaw?Petromyzon marinus lampreys and hagfish!

3. a.Does the fish have eyes on the same side and a flattenedbody? 4 no! b. Doesthe fish not have eyes on the same side and no flattened body? 5 yes!

4, a. Doesthe fish havea forkedtail? Hippoglossus hippoglossus Atlantic halibut! b. Doesthe fish not have a forkedtail? Pseudopleuronectesamericanus winter flounder!

5. a. Doesthe fish havefleshy fins withoutrays!? 6 yes! b. Doesthe fish have fins with rays? 7 no!

6. a. Doesthe fish havea pointedhead? Squalus acanthias spiny dogfish shark! no! b. Doesthe fish not havea pointedhead? Sphyrna lewini scalloped hammerhead shark! yes!

7. a. Is the fish body full moon-shapedwith a little caudalfin? Mola mola ocean sunfish! b. Is thefish bodynot distinctlymoon-shaped and has a highlyvisible larger caudal fin? 8

8. a. Is thefish club-shapedlike a baseballbat? Anarhichas lupus Atlantic wolffish! b. Is the fish body not club-shapedlike a baseballbat? 9

9. a. Is there evidence of a chin barbel? 10 b. Does the fish have no chin barbels? 13

10.a. Is thecaudal fin not notchedor only slightly just barely!notched? 11 b. Is the tail decidedly notched? 12

1 l.a. Doesthe fish havethree distinct dorsal fins top side!?Gadus morhua Atlantic cod! b. Doesthe fish havetwo distinctdorsal fins? Urophycis tennis whitehake!

95 12.a. Does the lower jaw extendbeyond the upper jaw? Pollachiusvirens Americanpollock! b.Does the lower jaw notextend beyond the upper jaw? Melanogrammus anglefinns haddock!

13.a. Does the fish have finlets sinallfins like growth between tail anddorsal and anal fin!? 14 b. Does the fish not have finlets? 15

14.a. Are thedorsal fins distinctlyseparated? Scomber scombrus Atlantic mackerel! b. Are the dorsalfins not separateddistinctly? Thunnus thynnus bluefin tuna!

15.a. Does the fish havea smalladipose fin smallfleshy fin betweenthe caudal anddorsal fin!? Osmerusmordant smelt! b.Does the fish not have a smalladipose fin? Pamolobus pseudoharegus alewife!

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ACTIVITY 2: AGING FISH

Information Determiningthe age of fishis very important for fishery biologists and aquaculturists. By examiningscales, it is possibleto determinean age profile of yourpresent fish population and makepredictions for the future. Knowledge of the age structure of a fishpopulation isimportant for managementpractices and conservationefforts. Givenadequate food and space,fish will continuallygrow. In this casethe oldestfish wouldbe the largest, but in nature,conditions are less than ideal and fish grow at varying rates. Food,space and other life requirementsare not equally distributed in theenvironment, and some fish aremore hardy and grow fasterthan others. Thereare a numberof methodsto calculatethe age of fish,Aging fish by scalecounts is themost widespread and straightforward method and can be conducted on live specimens without harmingthe individual. The limitations of thismethod isthat accuracy depends onthe interpretive abilityof theexaminer and the distinctiveness of the annual layers. Scales grow as the fish grows, producinggrowth layers which have a ring-likeappearance. Thescale and other hard parts of the fishgrow faster during the heavy feeding months of thesummer and slow down during bad feed- ingseasons, usually winter. When the growth subsides, the rings are closer together and appear darker,when observed under low microscopic magnification 0-40X!. Each of these darker rings is an annulusand usuallydernarks one year's growth. Theage of thefish can be roughly determined by counting the rings starting with the clear areaof thecenter called the focus or core. The focus represents the original scale of theyoung fish. In order to determinethe age of fish by studying the scale structure,several terms should be explained;

~Anntllus: Theannual mark or zoneon fish scaleswhich is formedonce a year. ~Focus: The small, clear area near the center of thescale which represents the original scale of the young fish. ~ CtenoidScale: The scale of a bonyfish teleost!which possesses small sharp spines ctenii!. ~ CycloidScale: The scale of a bonyfish withoutspines.

Thereare variations of thesescales. The spines of cteniiand the position of thefocus varieswith each species of fish.The annulus is recognizedin one of thefollowing ways: 1! "cross- ing over"where the onset of fall or wintercauses several ridges or circuli to flareoutward and end on the side of the scale, rather than circle the focus; 2! "discontinuous circuli" where the indi- vidualcirculi do notgrow together in a completeline becausethe scale stops growing and 3! extremecrowding of thecirculi whichoccurs first, prior to resumptionof growth.

Preparation Selectfish with largescales. These include fish suchas herring, alewife, bass, perch, had- dock,cunner, salmon, anchovy, and silversides. Other swift-swimming fish suchas the mackerel andtuna have reduced scales to enhancestrennlining. The scales of commoneels Anguilla!are microscopicor not present.You may obtain someof the abovefish from a local fish market, a seafoodprocessing plant, or a localfisherman, Fully-formed scales from eachspecimen should be selected.When a scaleis lost, the regeneratedscale does not form the old rings.Also, a false annualring is producedby femalesjust priorto spawningas reabsorption occurs. In addition,it is

99 difficultto agehatchery fish using this method. Hatchery fish undergo rapid, even growth within controlledenvironments. Their scales will nothave the annual dense groupings found oii scalesof fishthat experience seasonal food deprivation. Toprovide uniformity to thisprocedure, biologists usually select scales froin a specific spoton a fish. Follow theback edge of thedorsal fin downtowards the lateralline; removethe secondscale just above the lateral line. After the scales are selected and removed, they may be storedfor later use by placing them in anenvelope or by pressing them between pieces of paper. Thescales have their own cement called mucus. If possible,the paper that the scale is onshould be labeledwith the following information: type of species,weight, length, place, sex, and date. A usefulway to examinescales is toplace them between two layers of thinclear plastic and mount themin a 35-millimeter mm! slide blank. Scales are magnified by projectingthem with an ordi- nary35-mm slide projector. This method facilitates storing and cataloging and can be done by the wholeclass at once.Scales may also be examined under the stereoscope at 2040X. Detailed ex- aminationsof partsof thescales may also be of interest.A compoundmicroscope with 50-l00X objectiveswould be of someuse, especially for smallerscales if largeones are not available. Collectingscales from a largenumber of differentspecies of fishshows the variety of size andthe difficulty of age analysis. Start out with some of the easier specimens first, such as herring or haddock.A comparisonof bony fish scalesto the scalesof sharkswould also be of interest. Sharkshave a moreprimitive placoid type scale, which does not detach easily. The scale, which is verytiny, gives the skin a sandpaper-liketexture, Other types of scalesinclude those of thegar and theAtlantic sturgeon which have ganoid scales. Ganoid scales also do not detach easily. Large and pyramid-shaped,they give the skin an armour-likeappearance.

100 STUDENT HANDOUT Generalized Bony Fish External Anatomy

1. Maxilla and premaxilla Upper jaw! 11. Spiny dorsalfin firstdorsal! 2. Mandible Lower jaw! 12. Dorsal spine 3. Barbel 1 3,Soft rayed dorsalfin seconddorsal! 4. Nostril 14, Soft ray fin ray! 9. Eye 15. Adipose fin 6. Maxillary barbel 16. Caudal fin tail fin! 7. Cheek 17. Finlets 8. Operculum gill cover! 18. Anal fin 9. Pectoral fin 19. Anal spine 10, Pelvic fin 20. Caudal peduncle 21. Lateral line

Bony Fish Scale Types and Growth Rings

cteni annual annual ring ring radii

Cycloid Scaie Ctenoid Scale prom cod! |rom stnped bassr LAB HANDOUT Determiningthe Age of Fish ThroughObservation of Scales

Information Withincreasing demands on fish stocks around the world, it hasbecome very important to know theage composition of each type of fish.Such knowledge about the amount of growthgained each year,the life span of fish, and the age structure ofthe population, enables usto harvest fish crops moreefficiently and to enact conservation measures effective1y. Wewill age fish by counting the annualgrowth rings depositedon the scalesof fish.

Terms to know ~ Annulus:The annual mark or zoneon fish scales which is forinedonce a year. ~ Focus:The sinal1, clear area near the center of thesca1e which represents the original scale of the young fish. ~ CtenoidScale: The scale of a bonyfish teleost!which possesses small sharp spines ctenii!, ~ CycloidScale: The scale of a bonyfish withoutspines.

Materials Handlens or dissecting microscope, compound microscope slides, various species of fishor scales providedby teacher, metric tuler, projector, microprojector or slide projector, plastic sheeting, and empty slide if demonstrationsare desired!

Procedure 1.Remove a scalefrom several areas of eachspeciinen. Using a handlens or microscopeand the ScaleTypes and GrowthRings handout, deterinine if scalesare cycloid or ctenoid.

2. If thescale is ctenoid,remove further scales around the area of thepectoral fin. Cycloidscales shou1dbe taken from an area between the dorsal fin and the lateral line. Remove three scales from the indicated areaof eachspecimen.

3. Makea wetmount of thescales or placethem between two glassslides for microscopicobser- vation.Use both a compoundmicroscope and a stereoscope,

Observations Makeillustrations of the generalfeatures of the scalenoting: annuli, focus, circuli, and ctenii whenpresent!. Determine the distance between annuli on thescale by usinga metricruler. To determinethe age,each scale should be countedtwice, at different times, to arrive at an accurate interpretation.Count one year of growth for eachannulus.

Discussion Canyou differentiate between summer growth and winter growth? How? Each scale tells a story aboutthe iife historyof thatparticular fish. Choose a scaleand describe its life history.

Limitations and Sources of Error This could result in incorrect reading of scales. Some fish show no definite annuli. Other errors might resultin the useof imperfectsca1e or scalesthat havebeen rejuvenated, Errors in age determinationincrease with theage of thefish. Errorsmay also be madein determiningthe loca- tion of the first annulus-. 102 ACTIVITY 3'- BONY FISH DISSECTION

Preparation: If possible,select several different specimens andcompare their external features. The fish inay be freshor marine,as both have the same anatomical features. A diagramof theinternal and generalexternal anatomy ofa typicalbony fish is provided. Photocopy and distribute copies of the labhandouts Bony Fish Dissection Diagram, Generalized Bony Fish Zrternal Anatomy, and Gill Diagrams.More detailedanatomical figures are availablein marinescience lab manuals.

103 STUDENT HANDOUT

BonyFish DissectionDiagram

at zo

1. Brain 13. Unnary bladder 2. Swim bladder 14. Anus 3. Neural spine 15. Colon 4. Dorsal fin 16. Gonad 5. Kidney 17. Pelvic fin 6. Spinal cord 18. Adipose tissue 7. Vertebrae 19. Spleen 8. Adipose fin 20. Pyloric caeca 9. Caudal peduncle 21. Stomach 10. Caudal fin 22. Liver 11. Lateral line 23. Gall bladder 12. Anal fin 24. Heart

104 STUDENT HANDOUT

Gill Diagrams

gill arch artery 2.

ill filament

lamellae

Gill filaments are stacked and The major parts of the gills indude layered for increased surface area. the bony gill arch. The major blood vessels run through the gill arch and along the gill filament. Each filament contains several disc-shaped lamella,

rtery 4. ein

gill filament

The fish maintainsa one-wayflow of water through the gills by taking water into the mouth and passingit out throughthe gill slit or operculum.The water flows over the gills. Specifically, the gill filaments deflect the low0~ water so it will flow across the lamella. The blood flows in the opposite direction. The The lamella folds of tissue! contain water and blood fiow in counter directions the smaller branches of blood vessels across the lamella. This counter current flow known as capillaries, The exchange enhancesthe diffusionof oxygeninto the of gases occurs in the capillaries. blood,

105 STUDENT HANDOUT Bony Fish Dissection

Instructions Carefullyreadthrough thefollowing procedures andrecord observations accordingly.

ExternalAnatomy Shape l.Commonly, a fish'sbody is torpedo-shaped fusiform!and slightly ovoid incross-section, How ever,there aremany interesting departures fromthis idealized case.These range from globe shapes puffers-globiform! throughserpentine American eels-anguilliform! tothread-like forms snipes!.A flatfish likea flounderislaterally compressed orflattened fromthe sides, whereas a skateisdorso-ventrally compressedorflattened from the top.Whatis theshape ofthe fhh s! you are dissecting?

Body Covering 2.Many fish have thick skins which arecontinuous withthe lining ofall the body openings. Mucouscellsprovide a coating whichis both protective andeffective instreamlining thefish fors~imming. Doesyour specimen havea s! very tough skin? Does itfeel slimy?

3.Scales areusually imbedded inthe skin. They may be small orvery large. The types ofscales ganoid,cycloid, orctenoid! serve ascharacteristics ofmajor bony fish groups. Thetypes of scalesandthe number ofscale rows along oraround thebody aid in identification Whattype of scalesdoes your specimen have? s!Are they small or large?

106 Appendages 4. The appendagesof fish includethe variousfins andthe cirrhi fleshyprojections!. Fins are categorizedas median or paired.The dorsal top! fins showmuch variation. They may be continuous,partially divided, or completely divided into separate parts. The dorsal fin mayalso consistof eitherspines soft or hard!,rays, or both. Spines usually appear transparent, hard, and sharpat theends. Rays are soft and appear segmented when held to thelight or whenviewed undera low-poweredstereoscope. The rays may also branch out at the end. What type of dorsal fin s! doesyour specimen have. s! Does it haverays, spines, or both. Whatadvantage is there to having spinesor soft rays?

6. Othermedian fins includethe tail caudalfin! andthe anal fin justbehind the vent on the lower side!.The trout or salmon-likeforms have a fattyadipose fin. Finsalso may be reduced to a few disconnectedspines as in thestickleback. What function do you think the caudal fin serves?

7. Pectoralfins may vary also. They may be enlarged as in thesculpin, sea raven, or flyingfish, or moreregular in shape,as in thetrout andflounder. What function do you think thepectoral fins serve?

8. Pelvicfins vary in shapeand position. Their supportcomes internally from thepelvic girdle. Most soft-rayedfish havepelvics located abdominally, as in salmonids.They may be located belowthe pectorals, or theymay be under the throat jugular!.Some pelvics are modified, as in theshark and skate, to form claspersused in reproduction.Where are thepelvic fins on your fish? Whatfunction do you supposethey serve?

Internal Anatomy

9. Usinga scalpelor strongscissors, carefully cut openthe belly cavity,starting at theanal vent andproceeding up to thepectoral fins. For a betterview, remove a portionof thebody wall by startingagain at the analvent andcutting an arch-shapedline to the pectoralfins. Usethe internal anatomydiagram to helpidentify the structures.

107 10.Take the gill cover, called the operculum, offthe left side of the fish and observe thegills. If the specimenis fresh, note the red color produced by blood capillaries. Sketch the gill structure.

1 l.Identify the major internal organs. Make a diagramshowing theroute of the blood from the heart two-chambered!to the gills.

12.Study the digestive tract. Make an incision through the small intestines and a smallcross- section.Examine theinternal surface area. What is the color of the Bning of the digestive cavity?This lining is calledthe peritoneum, If it iswhite, the fish is generallya carnivore. Black indicates an herbivore.

13.Observe the swim bladder which is found under the vertebral column and kidneys. Note that it connectsto the esophagus. This flotation device is uniqueamong the bony fish andis very importantfor maintaining buoyancy. Can you express any air from theswim bladder?

14. Cutinto themusculature midway along the body. Are all themuscles white or are some red? Whatisthe approximate ratio of red to white muscle tissuein this region of the body? What doyou think the significance ofred muscLe cells is for a swimminganimal?

108 15.Choose an organ like the heart, liver, kidney, or spleen and cut a portionfrom it. Use forceps to blotthe cut surface ofthe organ on a microscopeslide.Allow slide to air dry and then quickly passthe shde once or twicethrough an alcohol burner flame. This will fix or stickthe blot to theslide!. Stain with a commercialquick blood stain for one minute. Rinse slide in tapwater andallow to air dry. View under a compoundmicroscope at40X or 100X.Draw a diagramof what you see.Label the red bLoodcells and the white blood celh.

109 MAKINGCONNECTIONS: ADDITIONAL ACTIVITIES AND EXTENSIONS ~ Culture Candidates Dividethe class into cooperative learning groups. Using the ABC Fish of the Gulf of Afaine obtainedfrom Maine Department ofMarine Resources! andthe NOAA Status ofthe Fishery Resourcesoffthe Northeastern UnitedStates obtained from Woods Hole Oceanographic In- stitute!,identify which species arecurrently being overfished. Divide the class into coopera- tivelearning groups andhave them choose oneof the fish principal groundfish orflounder! to research,Groups should research thepast and current status oftheir species, andits biology, ecology,and potential for culture. Groups will reporttheir findings to the class.

~ Cleaningand DressingFish Perhapsyou will havethe opportunity togo on a classfishing trip, or to obtain fish for the, dissectionwhich are suitable forcooking, For information oncleaning and dressing fish, refer to Appendix F.

GLOSSARY Adipose: Fat tissue. Anadromous:A species which leaves the sea to migrate upfreshwater rivers to spawn. Barbel:A tactilesense organ that is a threadlikegrowth Rom the jaw of somefish Bmod!C~ock:Adult fish retained for spawning Caudal: Referring to the tail. CaudalPeduncle: The nerve bundle from the tail region of a fish. Circuh:A ridge on a scalewhich can take many forms; often used in aging fish. Cteni:Small sharp spines on the comb-like edge of a ctenoidscale. Dorsal: Referring to backside. FertiTization:The union of spermand egg. FoodChain: The transfer of energyfrom one organisms to anotherin theform of food. Fry:The stage ina fish'slife from the time it hatchesuntil it reaches1inch in length. Gauoid:Diamond-shaped scalesthat are connected toone another byjoints. Grade: To sort fish by size. Groundfish.A marinebottom fish of commercial importance. HatcheryLocation where fish are raised from fertilized egg to juvenile. Incubation:Process bywhich eggs are placed ina favorableenvironment formhatching. Native:Species which have historically lived and reproduced in a particulararea, Operculum: Gill cover. Parr'A lifehistory stage which marks the first year of a salmonidslifecycle. Placoid;Primitive, tooth-like scales found on sharks, sosmall that they give the shark a sandpaper texture. Salmonid:Taxonoinic fish groupwhich contains salmon and trout. Smolt:A lifehistory stage which marks a juvenilesalmonid's physiological transformation tolife in a marine environment. Spawn:The mating of male and female organisms toproduce offspring, Superchill:The low temperature at which a particularspecies of fishdies. YolkSac: Source of nutritionfor fishimmediately after hatching.

110 ADDITIONAL RKSOVRCES Atlantic SalmonFederation. Fish Friends:A Curriculum Supplementfor Grades4, 5 & 6. St.Andrews, NB: Armour & Associatesand Gaynor/Sarty,Huntsman Marine Science Centre, 1995. Franzen,Nathan and Mark Wiley, Atlantic Salmon Teaching Guide. St. Andrews, NB: Atlantic Salmon Federation, 1991, Iversen,Edwin S. and Kay K. Hale.Aquaculture Sourcebook. A Guide to North American Species. New York: Van Nostrand Reinhold, 1992. MaineDepartment of Marine Resources. ABC Fish of theGulf of Maine.Augusta: DMR-Educa- tion Division, 1987. NationalFilm Boardof Canada.The Atlantic Salmon film!. Cat.no. 106C-0178-501. NortheastFisheries Science Center. Status of theFishery Resources Ogthe NortheasternUnited States.NOAA Tech.Memorandum NMFS-NE-108. Woods Hole, MA. Jan. 1995. Swift, DonaldR. Aquaculture Training Manual. Cambridge, MA: FishingNews Books- Blackwell Science Publications, 1993.

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