10-Mar-14 STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF FISHES Neutral Buoyancy and the Swim Bladder All fishes are slightly heavier than water To keep from sinking, sharks must always keep moving forward in the water Broad head and flat pectoral fins act as angled planes to provide additional lift The asymmetrical tail create lift when sweeping Neutral Buoyancy and the Swim Bladder Sharks have very large livers containing a special fatty hydrocarbon called squalene with a density of only 0.86 gr/mm The liver acts like a large sack of buoyant oil that helps to compensate the shark’s heavy body reduces shark’s specific weight! 10-Mar-14 Neutral Buoyancy and the Swim Bladder Swim bladders are present in most pelagic bony fishes but are absent in tunas, most abyssal fishes, and most bottom dwellers (flounders, sculpins) Neutral Buoyancy and the Swim Bladder Two types of swim bladder: + The more primitive physostomous (Gr., phys, bladder, stoma, mouth) fishes have a pneumatic duct that connects the swim bladder to the esophagus, through which they may expel air + More derived teleosts exhibit the physoclistous (Gr., phys, bladder, clist, closed) condition in which the pneumatic duct is lost in adults Neutral Buoyancy and the Swim Bladder + Gas is secreted into the swim bladder by the gas gland Gas from the blood is moved into the gas gland by the rete mirabile, a complex array of tightly-packed capillaries that act as a countercurrent multiplier to increase oxygen concentration + To release gas during ascent, a muscular valve opens, allowing gas to enter the ovale from which the gas is removed by diffusion into the blood 10-Mar-14 Osmotic Regulation Osmoregulators control the concentrations of salt and water in their bodies - In fresh water, an animal is usually hyperosmotic to the medium, and the osmotic gradient leads to an influx of excess water - In salt water, most vertebrates are hyposmotic; therefore, water tends to flow from their bodies into the surrounding environment Osmotic Regulation - Excess water is pumped out by the opisthonephric kidneys, which are capable of forming very dilute urine - Special salt absorbing cells located in the gill epithelium actively move salt ions, principally sodium (Na+) and chloride (Cl-), from water to the blood Together with salt present in the fish’s food, these absorption replaces diffusive salt loss A freshwater fish maintains osmotic and ionic Osmotic Regulation To compensate for water loss, a marine teleost drinks seawater Excess salt accompanying the seawater is disposed in multiple ways + Major sea salt ions (sodium, chloride, and potassium) are carried by the blood to the gills where they are secreted outward by special salt-secretory cells + The remaining sea salt ions, mostly magnesium, sulfate, and calcium, are voided with feces or excreted by the kidneys A marine fish maintains osmotic and ionic 10-Mar-14 Migration Migration (HUGH DINGLE AND V ALISTAIR DRAKE, BioScience • February 2007 / Vol 57 No 2): (1) a type of locomotory activity that is notably persistent, undistracted, and straightened out; (2) a relocation of the animal that is on a much greater scale, and involves movement of much longer duration, than those arising in its normal daily activities; (3) a seasonal to-and-fro movement of populations between regions where conditions are alternately favorable or unfavorable (including one region in which breeding occurs); (4) movements leading to redistribution within a spatially extended population 10 Migration of Freshwater Eels Eels are catadromous (Gr kata, down, dromos, running), meaning that they spend most of their lives in freshwater but migrate to the sea to spawn Adult eels leave the coastal rivers of Europe and North America, they swim steadily and apparently at great depth for to months until they reach the Sargasso Sea, a vast area of warm oceanic water southeast of Bermuda At depths of 300 m or more, the eels spawn and die Minute larvae - leptocephali (Gr leptos, slender, kephal-e, head) begin an incredible journey back to the streams of Europe and North America 11 Migration of Salmon Salmon are anadromous (Gr anadromos, running upward); they spend their adult lives at sea but return to freshwater to spawn species: + Atlantic salmon, Salmo salar (L salmo, salmon, al, salt): make repeated upstream spawning runs 12 10-Mar-14 Migration of Salmon After migrating downstream as a smolt, (a juvenile stage) a salmon ranges many hundreds of miles over the Pacific for - years and then returns almost unerringly to spawn in the headwaters of its parent stream Migration of Salmon - Salmons imprinted with the distinctive odor of the stream, which is apparently a mosaic of compounds released by the characteristic vegetation and soil in the watershed of the parent stream - They also imprint on odors of other streams they pass while migrating downriver Use these odors in reverse sequence as a map during the upriver migration as returning adults Migration of Salmon From the open ocean to the mouth of a coastal river: - Some fish (e.g Salmon) (like birds) can navigate by orienting to the position of the sun - Fish also appear able to detect and to navigate to the earth’s magnetic field - Fish use ocean currents, temperature gradients, and food availability to reach the general coastal area where “their” river is located 10-Mar-14 Locomotion in water 16 Hearing and Weberian Ossicles (Hickman, 2008, p 532-533; Kardong, 2008, p 693-694) 17 Respiration (Hickman, 2008, p 532-533; Kardong, 2008, p 409-421) 18 10-Mar-14 Feeding Behavior (Hickman, 2008, p 535-536; Kardong, 2008, p 248-256) 19 Reproduction and Growth (Hickman, 2008, p 538-539; Kardong, 2008, p 561-572) 20 ...10-Mar-14 Neutral Buoyancy and the Swim Bladder Swim bladders are present in most pelagic bony fishes but are absent in tunas, most abyssal fishes, and most bottom dwellers (flounders, sculpins)... to the medium, and the osmotic gradient leads to an influx of excess water - In salt water, most vertebrates are hyposmotic; therefore, water tends to flow from their bodies into the surrounding