1. How are fish classified? 2. Why are planktivores size-selective? 3. How many mating types are there in bluegill? Chapter 3 The Organisms

What is a fish? Phylum Chordata, Subphylum Vertebrata Lives in water Possess gills that are used throughout life Has fins

Major Classes of Living Freshwater Fishes Jawless fishes — lamprey Sharks and Rays – some rays live in tropical rivers Class Agnatha (Cephalaspidomorphi) Class Chondrichthyes Potamotrygon fws/Esyurui.html Lampetra richardsoni (western brook lamprey) markle/fishimages.html

Major Groups of Living Freshwater Fishes 2 classes of “Bony Fishes” (Osteichthyes) Class Sarcopterygii – lungfishes Class Actinopterygii – ray-fins Lepidosiren (South American Lungfish) Perca flavescens (Yellow Perch) families/yperch.html

Spiny rayed fish vs. soft rayed fish

Order Perciformes Contains over 9,200 species Largest order of vertebrates Very diverse group, but most are predators Sunfish Bass Yellow Perch

East African Cichlids lake_victoria.htm Haplochromis obliquidens badmanstropicalfish.com/ afcichlids.html Over 300 endemic species described from Lake Victoria, 500 from Lake Malawi and 160 from Lake Tanganyika (Order Perciformes)

Order Cypriniformes Family Cyprinidae (minnows and carps) About 286 species of cyprinids, in N. America, over 40% are “shiners” Emerald Shiner (Notropis atherinoides) fishing/fishid/remainder.htm

Size, shape, gape and position of the mouth often reflect diet and habitat Planktivore – eats zooplankton Piscivore – eats fish Detritivore – eats organic material from sediments Herbivore – eats plants Benthivore – eats food on the bottom Omnivore – eats plants and animals stewartsguideservice.com/ mixedbagarchive.htm catfish/catfish.htm

Planktivores eat zooplankton, but fish tend to eat more of some species and less of others. Which species do they select, which species do they avoid and why? Fish often select for larger, more visible prey items photo by M. Duffy There are 2 major reasons why...

Pumpkinseed Lepomis gibbosus 1. Encounter frequency: Encounter of large prey is higher than small prey Reaction distance —how close to the fish does a prey item have to be for the fish to see it and react to (eat) it? iafish/sunfish/pkse.gif Confer and Blades 1975 (L&O)

Reaction distance translates to overall volume searched, which influences vulnerability of the prey Volume searched = volume of sphere = 4/3 π r 3 Reaction distance = radius of sphere Visual field is roughly spherical with ~ 20º posterior blind segment Longer radius = higher encounter rate

2. Optimal foraging —take the prey that provides the greatest energy return for cost of capture/handing. With abundant prey, bigger is better Werner and Hall (1974) Ecology Fed fish choice of three sizes of Daphnia magna Prey size

Bluegills feeding on Daphnia Get exception to this “ bigger is better ” rule with small fish because of gape limitation Li et al Ecology Walton et al Ecology Selectivity Index No choice Avoids particular animals Selects for particular animals 0 +1 Small fish don ’ t eat large prey Daphnia size (mm) Fish > 76 mm Fish = 11 mm

Two morphs of Ceriodaphnia Big eyeSmall eye It is not just size that matters, it is overall visibility Artificially made small-eye morph more visible by feeding them india ink. Predation rate increased Zaret 1972 Fish always took the big-eye form.

Reproductive Behavior Most common type of reproduction is ovipary (external fertilization of eggs) Parental care ranges from broadcast spawning to mouthbrooding Many species build nests tlca/bass.htm

Graeb et al found that larval yellow perch ( 16 mm) avoided the nauplii and consumed the Daphnia. Explain this result