Biology of Fishes Exam 1 PDF

**Lecture \#1:** **Systematics:** study of relationships among species/lineages **Classification:** defining and naming groups of organisms **Taxonomy:** defining and naming species - 5 Nodes - 11 Branches ...

**Lecture \#1:** **Systematics:** study of relationships among species/lineages **Classification:** defining and naming groups of organisms **Taxonomy:** defining and naming species - 5 Nodes - 11 Branches  **Character/Trait: heritable feature possessed by an organism (anatomy, color, behavior)** - ex: hair present or hair absent **Synapomorphy: a shared, derived trait (closely related organisms, absent in other lineages)** - ex: milk production in mammals **Clade:** a group of organisms that includes the most recent common ancestor of all its members and all descendants of that common ancestor **Cladogenesis:** development of a new clade (splitting of a lineage into two -- speciation) **Anagenesis:** species changing over time **Convergence:** similarities that arose independently in two or more organisms that are not closely related (contrast with homology/synapomorphy) - ex: manatees and seals, analogous means of swimming **Derived:** describes a character state that is present in one or subclades, of a clade under consideration **Monophyletic:** (synonymous with clade) all members of a named group are derived from a common ancestor **Paraphyletic:** all members of a named group are derived from a common ancestor **Polyphyletic:** members of a named group are NOT derived from an immediate common ancestor (often a group was incorrectly defined via insufficient data) **Homology:** a trait that has been inherited from a common ancestor that also possessed the trait - ex: mammal forelimbs and bird forelimbs have the same bones in different configurations - this arrangement is shared with all tetrapods **Lineage:** any group of organisms connected by a continuous line of descent - ex: extended family (recent timescale), all mammals (deep timescale) **Outgroup:** a group of organisms outside the clade of interest, generally chosen because they lack characters important to the clade of interest OR chosen because they share characters with the clade of interest - ex: if the focal group is bats, the key question is about metabolism, an informative outgroup might be rodents. If about flight, the outgroup might be birds **Primitive:** describes a character that is present in the common ancestor of a clade. Inferred to be the original condition of that character in the clade - ex: the presence of hair is a primitive character state for all mammals, whereas the absence of hair is a derived character state for one subclade in Mammalia (whales and dolphins) **Sister group:** the two clades resulting from the splitting of a single lineage. Each clade is the "sister group" to the other. Both lineages are the same age, but the two clades are not necessarily the same age. **Taxa:** a broadly used term that can apply to any focal group - species - genus/family - ex: basses and salmon are taxa **Adaptation:** a feature that has a very specific function that acts to specialize the organism (may or may not be conspicuous) **Specialist:** an organism that performs best in very specific situations - ex: species only occur in caves, only eat algae **Generalist:** relatively unspecialized organism - ex: species that occur in lakes, ponds, and rivers **Benthic:** species with an affinity for the substrate/bottom - swims intermittently - swim for short periods **Pelagic:** species with an affinity for open water - swim constantly, occasionally coast but never sit still **Lecture \#2:** **Global diversity of marine fish:** - **More species at low latitudes (near the equator). Why?** - Stable conditions (no seasonality) - More food availability - More space - **Species accumulate faster at high latitudes (near poles) Why?** - Unstable conditions (seasonality) - Fewer species - **Competitive exclusion principle:** species can be competitively excluded from a niche by dominant/abundant incumbent species - Lots of species competing near the equator - Less comp near poles - **Can also be concentrated in some coastal areas** - Coral reefs are largely restricted to tropical areas between 30˚ and -30˚ latitude - **Provide complex structures for fishes** - Lots of food - Shelter from larger predators **Global diversity of freshwater fish:** - **Loosely concentrated near the equator, but mainly on large landmasses with large, warm river systems** - Amazon and La Plata Rivers (South America) - Congo River (Africa) - Mekong and Yangtze Rivers (Asia) - **Mississippi River (North America)** - Extends from Louisiana to New York to Saskatchewan - Through 39 states - Third largest river in the world - \~350 species **Lecture \#3:** **Agnatha: Jawless fishes** - The first vertebrates were jawless fishes (originated in the Cambrian period) - **Myxiniformes (Hagfishes)** - **External anatomy:** - Vestigial eye, 4 pairs of sensory tentacles, mouth with rasping tongue and keratin teeth, mucus gland pores (\~100 along each flank), 12 external gill slits (paired), and a caudal fin - Slime defense mechanism - Mucus glands excrete mucin vesicles (balls of mucus), skeins (balls of fibrous thread), upon contact with seawater they uncoil - Chondrocrania: minimal, rudimentary structures made of cartilage - Feeding: Protract tooth plate, Anchor teeth into flesh, relax protractor muscle, tie their body into a knot, Pry flesh away by torquing their body and pulling head through the knot - **Petromyzontiformes (Lampreys)** - **External anatomy:** - Eye, oral disc with keratin teeth and rasping tongue, 7 external gill slits (paired), anterior dorsal fin, posterior dorsal fin, caudal fin - Chondrocrania: minimal, rudimentary structures made of cartilage - Neural arches: rudimentary cartilaginous spine - Each gill is located within a pouch - **Feeding:** - Swim forward to expand oral disc against flesh - Teeth passively anchor into flesh and create a holdfast (suction cup) - Rasp away skin and flesh with tongue to create wound - Feed upon blood - **Agnatha: Hagfishes and Lampreys** - **Generalities:** - Elongate, tubular body - Gills arranged in separate pouches (water drawn in and expelled out through slits) - Rudimentary chondrocranium and cartilaginous skeleton - Lack scales - Lack paired fins - Lack jaws - Living representatives of the oldest lineage of fishes **Lecture \#4:** **Chondrichthyes: Cartilaginous fishes** - **Ratfish/Chimeras, Rays, and Sharks** - **Buoyancy:** - spend most of their life along the bottom - passively maintain buoyancy in two ways: A large oil-filled liver and a heterocercal caudal fin (shark tail). - **Gill openings are independent and physically separate but connected to the esophagus** - Water directed across each gill - More efficient than pouched gills, utilizing fish forward movement - Energy used for locomotion benefits respiration - **Modes of respiration:** - Slow-moving, benthic sharks actively pump water across gills with mouth movement (nurse sharks) - Spiracle pulls water in and across gills, active process (most rays) - Ram ventilation, forward movement passively forces water across gills, a passive process that requires swimming (large pelagic sharks, must swim to breathe) - **Placoid scales:** - Present in all species - Dermal denticles made of dentine and enameloid - Lightweight, highly protective, reduced drag - Some scales modified into auxiliary defense mechanisms (dogfish dorsal spine, stingray spine) - **Teeth:** - Made of calcium phosphate - Smooth or serrated - Replaced throughout life - Usually shed by falling out during feeding - **Depend on prey:** - Mammals, fish: large, pointy teeth for grasping and cutting - Mollusks: rounded and flat teeth in plate form for crushing - **Ampullae of Lorenzini:** - Electroreceptors that detect electric fields - Form a network of gel-filled pores across the shark's surface, concentrated around the snout and mouth - Gel-filled ducts connect to bulbs lined with kinocilium (sensory hairs attached to sensory cells that transmit info to nerves) - Provides magnetoreception which assists with long migrations - **Synapomorphies: (shared by all members)** - Skeleton is cartilaginous - Chondrocranium (skull) lacks sutures - Soft fin rays (Ceratotrichia) are unsegmented - Teeth not fused to jaws - Males have claspers, derived from the margin of the pelvic fin that allows for internal fertilization - **Chimeroidea: Ratfish/chimeras** - 58 species - Gill cover over 4 gill slits - Live at depths from 80-2600m - Mostly scavengers or invertivores (eat inverts) - Upper jaw fused to the chondrocranium (not mobile) - Males have cephalic claspers (unknown function) - **Elasmobranchii: Selachii (sharks) and Batoidea (rays and skates)** - Oldest fossil teeth from 418 Mya - Spiracle: vestigial or modified gill slit - **Selachii: Sharks** - **Skeletal anatomy:**  - Skeleton is cartilaginous - Pelvic fins usually not anchored to the skeleton by the pelvic girdle - Soft fin rays unsegmented - **Chondrocranium, jaw, and branchial anatomy** - **Batoidea: Skates and rays** - **Skeletal anatomy:**  - **Anatomy: Skates vs. Rays** - Rays are live-bearing (viviparous), skates are egg-laying (oviparous) - Skates typically have a prominent dorsal fin, rays usually absent or greatly reduced dorsal fin - Rays are kite-shaped with ship-like tails, 1-2 spines - Skates have fleshy tails and lack spines **Lecture \#5:** **Sarcopterygii: Lobe-finned fishes** - **Dipnoi (Lungfishes):** cosmoid scales (extinct) cycloid scales (extant) - **Distribution of extant species is due to the breakup of that Gondwana landmass** - **Burrowing mechanism:** - **Aestivation:** - Period of dormancy - Emerge with the return of wet conditions - Lungfish can survive up to five years in necessary - **Cranial Anatomy:**  - **Bony skeleton:** - Ceratohyal (floor of mouth), clavicle (part of pectoral girdle), and cranial rib (an accessory structure associated with their lung) are involved in breathing and feeding - Breath by gulping air from the surface - Skull and jaw movement during breathing and suction feeding are generally similar, including the same sequence, but motions are faster early when feeding - **Scales:** - **Extinct lungfishes:** - Cosmoid scales: - Benefit: durable and defense against predators/parasites - Drawback: poor flexibility restricts body movement - **Extant lungfishes:** - Cycloid scales: - Benefit: flexible and enable mobility - Drawback: limited defense against predators - **Actinistia (Coelacanths):** - **Vestigial lung derived from the swim bladder** - Filled with fat, rather than air, likely adapted for the buoyancy at great depths - **Cosmoid scales:** - Likely derived from the fusion of placoid scales - Made of two inner layers of vascular bone - Middle layer of cosmine - Outer layer of enameloid - **Polypteriformes (Reedfishes): \~360 Mya** - Juveniles have external gills, resorbed over time - Respire using lungs, but cannot extract sufficient oxygen from water (not enough surface area for gas exchange) - Must periodically surface and gulp air - **Spiracular breathing:** - Respire through two spiracles on the top of the head - Rest with head on the water surface - Air can pass through spiracles into mouth - Gulp air with mouth if oxygen is extremely limited - Expel air through gill slits or from the mouth - **Culminates in the ability to survive short periods on land** - If habitat is desiccating, they can make short over-land excursions in search of better conditions - **Acipenseriformes: Sturgeons and paddlefishes** - **Acipenseridae (Sturgeons): \~350 Mya** - 28 species - Lack scales, possess five lateral rows of bony plates called scutes - Four barbels (sensory organs in front of mouth) - Lack teeth - Skeleton is largely made of cartilage; derived trait, many bones do not fully ossify - Commercially harvested for their eggs - **Polyodontidae (Paddlefish): \~350 Mya** - 8 species; only 2 extant - **Rostrum has 2 functions:** - Provide lift and stability while filter-feeding - Counteract the drag created by the lower jaw that drops below the body - Lack teeth - Lack scales - Ampullae of Lorenzini present in ancient bony fishes (lungfish, coelacanths, reedfish, sturgeons, paddlefish) - **Amiiformes (Bowfins): \~250 Mya** - **Only 2 species** - *Amia calva,* occurs throughout the Atlantic coast - *Amia ocellicauda,* occurs throughout the Mississippi River Basin - Very old lineage - **Vascularized swim bladder can function as a lung** - Small pneumatic duct corrects the foregut to the swim bladder - Gulp air in poorly oxygenated warm water - Can survive in hypoxic conditions by gulping air at the surface - Protruding tube-like nostrils - Single-layered cycloid scales - **Lepisosteiformes (Gars): \~250 Mya** - 7 extant species - Vascularized swim bladder can function as a lung exactly like the Bowfins above - **Ganoid scales (reedfish/bichirs/gars)** - Rhomboid shape - 3 layers - Inner bony plate - Middle layer of osteodentin - Outer layer of ganoine - Largely non-overlapping - Inflexible and tough - Benefit: durable and defense against predators/parasites - Drawback: poor flexibility restricts body movement **Lecture \#6:** **Actinopterygii: Ray-finned Fishes** - **Elopiformes (Tarpon):** - 2 species - Cycloid scales - Both species can live in marine and brackish water, including short durations in freshwater - **Obligate air breathers:** - Have a vascularized area of the swim bladder that diffuses air into the blood - Must have access to the surface - Likely a unique origin from that in lungfish, reedfish, sturgeons, paddlefish, bowfins, and gars - **Anguilliformes (eels):** - **True eels** - **Scales:** - Freshwater: small, soft, think cycloid scales embedded in their epidermis - Marine: lack scales, instead produce mucus to protect their bodies from abrasion - **Freshwater eels are derived from marine ancestors** - **Freshwater = derived** - **Marien = primitive** - Eels lost scales - Scales re-evolved when some eels moved into freshwater - Suggests that lacking scales viable in marine, but not freshwater environments (flowing streams too physically abrasive, parasite-load too high in freshwater) - **Fins** - Freshwater: pectoral fins and continuous dorsal, caudal, and anal - Marine: continuous dorsal, caudal, and anal. NO pectoral fins - **Osteoglossiformes (arapaima, arowana, elephant fishes):** - "Bony tongues" - \~245 species - Almost exclusively freshwater - Cycloid scales - Most teeth located on the tongue and roof of mouth - **Ostariophysi (carps, minnows, catfishes, tetras, knifefishes):** - **Weberian apparatus:** - Set of minute bones connecting the inner ear to the swim bladder - All structures derived from the first four vertebrae - Four main components: *claustrum, scaphium, intercalarium, and tripus* - Amplifies sound waves as the swim bladder acts as a resonance chamber - Provides an enhanced ability to sense vibrations and hear - \~11,000 species - All freshwater, distributed on all continents except Antarctica - **Cypriniformes (carps, minnows, suckers):** - \~4,500 species - Cycloid scales - Lack teeth on jaws - Lack stomach - Many have barbels (whiskers) - **Characiformes (tetras, piranhas):** - \~2,200 species - Adipose fin, distinct character (tiny fin by caudal fin) - Cycloid scales - Well-developed teeth - **Gymnotiformes (knifefishes):** - **\~240 species** - **Lack pelvic and dorsal fins** - **Posses electric organs that produce weak electric fields** - Too weak to harm other fish - Used to navigate the environment - EXCEPTION: electric eel can stun prey - **Siluriformes (catfishes):** - \>3,800 species - Majority freshwater - Adipose fin distinct - **Usually negatively buoyant** - Reduced swim bladder - Large bony skull - Facilitates benthic lifestyle - Mouth is not protrusible, and the upper jaw is immobile - Lack scales, produce mucus - "Armored" have dermal plates or plates derived from vertebral processes - Sound production, produced by flicking their pectoral fins forward and dragging the spines across the cleithrum (pectoral girdle) - Barbels (whiskers) up to 4 pairs: nasal, maxilla, and 2 pairs on dentary - Always occur in pairs, some can be absent - **Some breath air** - Gulp air into the modified swim bladder - Diffuse air through modified gill arches - Gulp air into the modified stomach/digestive tract - **Esociformes (pikes and mudminnows):** - **Esocidae (pikes) 7 species** - North America, Western Europe, Siberia - Sportfish and top predators - **Umbridae (mud minnows) 3 species** - Mississippi River basin and throughout the Eastern US - Usually in stagnant, low-oxygen waters (marshes, ditches, swamps) - **Salmoniformes (salmon, trout, chars, whitefishes, graylings):** - Food and sportfish - Adipose fin - **Percopsiformes (trout and pirate perch, cavefishes):** - Chologaster (swamp fish) live near the surface - Forbesichthys (spring cavefish) live in intermittent surface - Typhlichthys (southern cavefish) live in sub-surface - **Cave-adaptation:** - **De-pigmentation:** - Loss of selection for visual signaling - Colors are expensive to make - **Eye-loss:** - Expensive structures - Require vitamins to maintain proper function - Limited utility in the dark - **Elaboration of the lateral line system:** - Primary sensory system - Provides mechanosensory function (vibrations) - Provides chemosensory function (smell) - Often appears as vertical striations along the head and body - Each pore contains sensory hairs - **Flattening of head:** - Suspiciously common - Possibly to increase mouth size - Increase surface area for sensory receptors - May be due to truncated development **Lecture \#7:** - **Percopsiformes Continued:** - Cave-adapted species are not each other\'s closest relatives - Lineage colonized cave environments 3 separate times - Distribution of lineages doesn't correspond to cave system, river drainage, or aquifer - **Acanthomorpha (spiny rayed fishes):** - **All species possess hollow and unsegmented spines along the anterior portion of the dorsal and anal fins** - Can be extended and function as a defense mechanism - Can be retracted to reduce drag while swimming - Possess well-developed cartilage around the snout permitting the upper jaw to protrude - **Mostly ctenoid scales** - Outer bony layer, inner fibrous layer made of collagen, posterior edge lined with small spines - Benefit: highly flexible, enabling mobility, comb-like edge creates turbulence that reduces drag - Drawback: provides much less protection than placoid, Cosmoid, or ganoid scales - Some cycloid scales - **Holocentriformes (squirrelfish and soldierfish):** - Nocturnal - Large eyes -- helps in dim light - **Usually reddish color** - Provides camouflage in dim light - Red light is filtered out first - Poorly visible to predators - Marine - **Batrachoidiformes (toadfish):** - Marine - **Gobiiformes (gobies):** - 90% marine - Small burrowing species - **Lack swim bladder** - Must actively swim upward to avoid sinking to the bottom - Spend most of the time resting on the bottom - **Scombriformes (cutlassfish, mackerel):** - Marine - Majority pelagic, active swimmers - Fastest swimmers - Large predators - **Sportfish** - **Syngnathiformes (seahorses, sea dragons, pipefishes):** - Marine - Mimic seaweed or coral (crypsis) - Males become pregnant and carry young - Loss of fins (pelvic sometimes caudal fin) - Seahorses have prehensile tails used to grasp - Slow swimmers - **Synbranchiformes (spiny eels, climbing perch, gouramis, bettas):** - Freshwater - **Labyrinth organ:** - Branchial accessory organ - Derived from first epibranchial (dorsal portion of gill arch) - Series of skin folds result in vascularized area in which inhaled oxygen can be diffused into the blood - Survive several days on land if moist - Present in climbing perch, bush fish, gouramis, and bettas - **Carangiformes (jacks, trevally, remoras):** - Mostly large laterally compressed, silvery fishes - Remoras have a modified dorsal fin that forms an oval disc-like organ that functions as a suction cup - Made of stout, flexible membranes that can be raised and lowered to create or release suction - Can slide backward to increase suction - Can release itself by swimming forward - Many species are host-specific, often attaching to sharks and whales - smaller species may attach to sea turtles, tuna, or swordfish - Commensalism (phoresy) -- attachment to host for travel - Marine - **Pleuronectiformes (flatfishes):** - Nearly clear as juveniles - Exhibit eye migration during early development - Majority are marine - **Ovalentaria:** - Produce adhesive eggs that are attached to the substrate - **Pomacentridae (damselfishes and clownfishes):** - Most species farm plots of algae - Longfin Damselfish has a mutualistic relationship with Mysidium integrum - Clownfish have mutualistic relationships with anemones - **Polycentridae (Leaf Fishes):** - Crypsis: mimic dead leaves, ambush predators - **Cichlidae:** - \~1,700 species - East African Great Lakes - Conceptually the opposite of the 'living fossils' - Exhibit a significant paradox - Distributed throughout Africa, the Americas, India, and Madagascar - Freshwater fishes **Lecture \#8:** **Acanthomorpha (spiny rayed fishes):** - **Perciformes:** - **Triglidae (sea robins):** - Possess sensory organs derived from pectoral fins - Used to sift through the substrate for food - Marine - **Percidae (perches and darters):** - Large-bodied predators (walleye and perches): sport and food fish - Dramatic transition to small bodies (darters) - Further reduction in body size (darters) - Darters lack swim bladders -- strictly benthic - Freshwater - **Centrarchiformes:** - **Centrarchidae (sunfishes and black basses)** - **Labriformes (wrasses (\>400 species) and parrotfishes (\~90 species)):** - Most wrasses and all parrotfishes are associated with coral reefs - Parrotfishes are a sub-clade of wrasses - Parrotfish teeth are fused into a "beak" with two segments on the upper jaw and two segments on the lower jaw, each meeting along the fish's midline - Fused teeth are used to graze on coral - **Lophiiformes (anglerfishes and frogfishes):** - **Mass is mostly head and jaws** - Infrequently encounter large prey but large mouths ensure they can eat whatever they come across in the deep sea - **Lure they use to attract prey: frogfish lures mimic invertebrates, anglerfish lures emit light to attract prey** - Illicium (rod/stalk): modified dorsal spine that is controlled by muscles to move the lure - Esca (bait/lure): luminescent organ that houses symbiotic bacteria that produce light  - **Tetraodontiformes (pufferfishes, file fishes, triggerfishes):** - Many fins lost or functionally lost - Clavus: a pseudocaudal fin that acts as a rudder **Lecture \#9:** **Fish Swimming Modes:** - **Body-caudal fin (BCF) swimming:** - **anguilliform swimming (eels): swimming with most of the body and caudal fin** - high maneuverability and flexibility - slow speed - low hydrodynamic efficiency - swimming often interrupted by periods of inactivity - body cylindrical and elongate - pointed head - paired fins reduced or absent - **carangiform swimming (jacks): swim with posterior body region and caudal fin** - intermediate maneuverability, flexibility, and hydrodynamic efficiency - slow-medium speed, near constant swimming - laterally compressed - often very narrow in front of tail - rounded or blunt head - fins pointed - **thunniform swimming (tunas): swim with caudal fin** - intermediate body flexibility - low maneuverability - high hydrodynamic efficiency - ideal for constant, medium-to-high speed swimming - laterally compressed - often very narrow in front of tail - pointed head - fins pointed - **ostraciform swimming (boxfishes): swim with caudal fin (very little motion)** - very little body flexibility - high maneuverability - very slow speed - low hydrodynamic efficiency - large pectoral fins - usually "steer" with tail - other fins often reduced or vestigial - **Median-paired fin (MPF) swimming:** - **labriform swimming (wrasses): swim with pectoral fins** - intermediate body flexibility - intermediate maneuverability - slow speed - intermediate hydrodynamic efficiency - often swim in bursts (flap, coast to halt, repeat) - characterizes many coral reef fishes - laterally compressed - long, tapered pectoral fins - otherwise, super variable - **rajiform swimming (rays): swim with pectoral fins** - low body flexibility - low maneuverability - slow speed - high stability (resistant to rolling or tipping) - low-to-high hydrodynamic efficiency - dorso-ventrally compressed - expanded pectoral fins - benthic species have dorsally positioned eyes - **gymnotiform swimming (knife fish): swim with anal fin** - low body flexibility - high maneuverability - slow speed - anal fin expanded along the body (can be continuous with caudal) - laterally compressed - **amiiform swimming (bowfin): swim with dorsal fin** - low body flexibility - high maneuverability - slow speed - elongate (maximize length of dorsal fin) - tubular shape - **balistiform swimming (triggerfish): swim with dorsal and anal fin** - low body flexibility - high maneuverability - slow speed - tapered head and body (triggerfish and pufferfish) - laterally compressed (triggerfish) - rounded body (pufferfish) **Caudal fin types:** - **Protocercal:** - Undifferentiated - Symmetrical - Lampreys and hagfishes - **Heterocercal:** - Unequal-lobed (upper larger) - Asymmetrical - Passively generated some lift - Sharks and sturgeons - **Hypocercal:** - Asymmetrical (bottom larger) - Uncommon - Flying fish -- creates passive drag to keep them from drifting high above the water - **Homocercal:** - Symmetrical - Most common - Most variable in shape - Tunas and wrasse - Sub-types: - Rounded (sunfishes) - Truncate (darters) - Lunate (tunas) - **Hemihomocercal:** - Asymmetrical (without lobes) - Abbreviated homocercal - Bowfin and gar **Lecture \#10:** **Locomotion:** - **Most species use their pectoral fins to some degree** - **carangiform/thunniform:** use long, stiff pectoral fins for steering at moderate-to-high speeds - **ostraciform/balistiform:** use flexible pectoral fins to supplement dorsal and anal fins for propulsion and steering - **Some species that rarely use their caudal fin, will do so in certain situations** - **labriform/amiiform swimmers:** use tail to generate a burst of propulsion if necessary - **Anguilliform swimmers:** usually benthic and often complex habitat - **Carangiform/Thunniform swimmers:** pelagic, open water away from structures - **Ostraciform swimmers:** coral reefs but not necessarily benthic - **Labriform swimmers:** coral reefs but rarely benthic - **Rajiform swimmers:** - if they undulate their pelvic fins: benthic, simple or moderately complex, often sandy areas (many species burrow) - if they oscillate their pelvic fins: pelagic, open water away from structures - **Gymnotiform swimmers:** complex habitat (vegetation, stumps, etc.) but not benthic - **Amiiform swimmers:** variable habitat, either complex (vegetation, stumps, etc.) or areas without structure - **Balistiform swimmers:** complex habitat