Food & Feeding

Food & Feeding I. Food types (fish diets) II. Morphology of feeding structures III. Feeding tactics & Mechanics IV. Diversity of feeding in fishes V. Importance of Feeding • • • • • • must eat to survive size often influences susceptibility to predators fish never stop growing maturity is a function of size more food → more energy for growth & reproduction higher foraging rate → higher fitness Trophic structure I. Diets of Fishes General Food Habits Herbivores: opaleye, halfmoon (<10% of spp. in CA) Detritivores (scavengers): mullet Omnivores: killifish, topsmelt Carnivores: primary - anchovy, gobies secondary - various spp. surfperches tertiary - basses, bonito, mackerel Feeding types (another way of classifying fishes) 1. Predators - take large whole (or part) items grasping, pointed teeth 2. Grazers (browsers) - plant and animal - small bits – algae 3. Plankton feeders Strainers (filterers) - small and large – herring, anchovies, whale sharks Pickers – protrusible jaws – blacksmith, kelp perch, pipefishes 4. "Suckers" - large amount detritus (detritivores), but plants also – mullets, suckers (FW) 5. Parasites - lampreys, pearlfish, candiru Most fish are opportunistic though II. Morphology of Feeding Structures • great diversity of feeding modes is allowed by complex feeding structures Parts of the feeding & digestive system • mouth —structure – lips – key bones: premaxilla & maxilla, mandible – pharyngeal jaws – teeth —placement • gill rakers • stomach • intestine fangtooth 1 Lips • “form follows function” – thin in planktivores (e.g., Chromis sp.) – thick, fleshy, tactile, w/ taste buds in bottom foragers Mouth Bones • premaxilla, maxilla, dentary (mandible), several other skull bones – thick & tough in many large predators (e.g., giant seabass, sheephead) primitive – fused maxilla & premaxilla Mouth Bones advanced – separate maxilla & premaxilla Pharyngeal Jaws • “throat jaws” – bones plates w/ projecting teeth • second set of jaws allows different uses of primary jaws – increased range of food types – evolved as modified gill arches – morphology varies with diet Teeth • hugely variable in shape and size (absent in many “advanced fishes) • found on many structures – jaw bones, pharyngeal jaws, roof of mouth, etc. Teeth • types – viliform (elongate, needlelike), e.g. gars, needlefish, lizardfish – blade-like, triangular, e.g. sharks, piranhas – caniniform (fang-like), e.g. snappers – cardiform (numerous, small, pointed, sand paper-like), e.g. snook, bass, billfish – molariform (flattened, grinders), e.g. carp, croakers, eagle rays 2 Mouth Placement – reveals much about diet • superior mouths: fishes that ambush prey from below (e.g., stargazers, hatchetfishes, frogfishes • terminal mouths: highly mobile predators that feed on highly mobile (often schooling) prey (e.g., tunas, sea basses) • inferior mouths: demersal predators that feed on bottom-dwelling prey items such as crustaceans, bivalves, etc. (e.g., horn sharks, catfishes, suckers) • tubed-snout fishes: fishes that feed on prey items that dwell or hide in crevasses, under substrates, etc. (e.g., elephantnoses, butterflyfishes) Gill rakers • form follows function: – long, fine, closely spaced in filter feeders – shorter, stout, sharp, & widely spaced in piscivores – short and stubby in eaters of shelled invertebrates – intermediate (length, spacing, thickness) in fishes w/ mixed diets Stomach planktivore • most fish have stomachs, but some lack them (e.g., plankton feeders, herbivores, parasitic fishes) • some highly muscular, gizzard-like (mollusk eaters, some herbivores) • acidic: HCl and pepsin (digestive enzyme) break down proteins) piscivore microcarnivore Intestine • length correlated with diet – herbivores: long & coiled (2-15x body length) – carnivores: short (1/3-2/3 body length) Intestine • intestine length in various fishes 3 Specializations for herbivory: herbivores have long guts III. Feeding tactics: how fishes feed A. Oral manipulators 1. scrapers, e.g. parrotfish, surgeonfish, Plecostomus 2. biters, e.g. piranha, some sharks 3. etc. gut length : body length B. Ram feeders: swim mouth around prey 1. Continuous swimmers herbivore omivore carnivore a. strain small food, e.g. whale shark b. chase down prey, e.g. tunas, jacks 2. Sit and wait or stalkers, e.g. pike, lizardfish, barracuda C. Suction Feeders (“inertial suction”) Oral Manipulators cutting: tiger shark grasping: lizardfish • • most fishes allows great diversification of diet • the key to evolutionary success of many fish groups? Ram Feeders rasping: damselfish chiseling: parrotfish crushing: wrasse tearing: eel Suction feeding & jaw protrusion – keys to evolutionary success of fishes Suction Feeders sit & wait predators planktivores • • • • • • suction depends in part on jaw protrusion allowed by freeing of premaxilla and maxilla generates negative pressure in mouth (buccal cavity) most fish use it at some point during feeding especially important to planktivores and piscivores mechanics -- increase volume of buccal cavity by: – elevate neurocranium – drop “floor” of mouth – move sides of mouth out (laterally) – lower mandible & protrude premaxilla 4 Suction feeding Increase volume of oral cavity Mechanics of jaw protrusion & suction Decrease volume of oral cavity Functional advantages of jaw-protrusion Jaw Protrusion in the Sling-Jaw Wrasse • jaw protrudes up to 65% of head length (twice that of any other fish) 1. Prey can be sucked in from as far away as 25-50% of head length 2. Increases attack velocity by up to 40%: mouth can surround a prey much faster than if by ram feeding 3. Increased handling ability and swallowing ability http://www.youtube.com/watch?v=pDU4CQWXaNY&feature=player_embedded IV. Diversity of Feeding in fishes Diversity of Cichlid species (~1000+) in African Great Lakes allowed by flexibility in foraging habits • African cichlids as an example • about 1000 species evolved from a single body plan & a handful of ancestral species 5 African Cichlid foraging habits: examples & convergent evolution V. Trophic Structure -- who eats whom Kelp forest fish assemblage trophic structure megacarnivore mesocarnivore microcarnivore Bay/estuary trophic structure Epipelagic trophic structure • Six trophic levels! • No herbivorous fishes 6