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Brown trout, Salmo trutta Brook trout, Salvelinus fontinalis Rainbow trout, Oncorhynchus mykiss Hatching Fingerling, 6 mo Sac fry, alevin, <6 wk Fry, ~6 wk Adult 2-3 yr Fish Fish dominate the ______________ in most lakes, streams, rivers and estuaries. Their large size and _________________ greatly influence the biological structure of aquatic ecosystems. Fish occupy several different levels of the aquatic food chain and comprise over ____________ of the earth’s vertebrate species. Fish are the main ______________ product harvested from inland waters. _________________ recognize that fish yield is a function of the whole-lake or stream production process. Fish are almost ____________, except in mountain lakes where it is _____________ impossible for fish to pass upstream over large waterfalls that guard the lake; except when ______________ has completely changed the natural balance. Distribution and ____________ preferences Fish are masters of the turbulent water environment except for early _____________ life stages. Fish actively _______ sites for feeding, breeding, and resting. The chemical and biological features of littoral habitats is directly correlated with the _______ (richness) and ________ of fish species. Many lake fish show strong preferences for a habitat that includes a diverse collection of __________ and emergent _____________. Important aspects of the submerged vegetation that attract fish include: _______________ of the plants density of the animal ____________ species ____________ High plant diversity supports a great diversity of _____________________ that are food for the fish. Additionally, a rich ____________ layer coating most submerged vegetation feeds small juvenile fish which use this vegetation as a refuge from ___________________. Divisions of freshwater fish groups I. Primary Groups with little or no ___________ for seawater; lungfish, paddlefishes, pikes, minnows, catfishes, centrarchids (___________), etc. II. Secondary Groups usually ___________________ but with enough salt tolerance so that members can enter the ocean and sometimes cross ______________________ some gars & pikes, killifishes, live bearers (perch), cichlids. Paddlefish, Polyodon spathula Northern pike, Esox lucius Warmouth (sunfish), Lepomis gulosus Mummichog (killifish), Fundulus heteroclitus Yellow perch, Perca flavescens Blue tilapia, Tilapia aurea III. _______________ Migratory between freshwater and the sea for purpose of _____________. ______________: diadromous fishes which spend most of their life in the sea and mature. When fully grown they return to _____________________. ______________: diadromous fishes which spend most of their life in freshwater and go to sea as adults to breed. _________________: regularly migrating between freshwater and the sea for purposes other than breeding. Marine: spawning in marine water, with larvae and juvenile stages briefly in freshwater (______________). Freshwater: spawning in fresh water with larvae and juvenile stages; ____________________ before returning to freshwater. _______________ Estuarine fishes that often and freely go between marine and freshwater, differing from above categories which usually are capable of changing mediums ________________________. __________________ in freshwater fishes Freshwater fishes are ________________ to their medium and tend to gain water by diffusion through any ______________________. If uncompensated, the inward diffusion would dilute the body fluids to the point that the their necessary ________________ functions could no longer be accomplished. A state referred to as “________________” How do they compensate? Can’t waterproof (______). A balance must be maintained by driving the ____________. Osmoregulation The task of removing water is accomplished by the kidney. The kidneys of freshwater fish are capable of excreting urine that is more _______________________. Additional contribution to ion balance by the urinary bladder: ____________________ of Na+ and Clthrough the wall of the bladder. Osmoregulation Although the concentration of salt in urine is low, the _______________ causes a significant amount of salt to be lost. Salts are also lost by ____________ from the body. Losses are balanced by __________ in food and by ________ absorption through the gills. Distribution and habitat preferences Temperature and _________________ also regulate fish distribution and habitat preferences. There is a wide variety of thermal preferences both among species and __________________. Three thermal categories are: cold-water cool-water _____________ fishes __________ often prefer temperatures that are several degrees warmer than adults of the same species. Thermal preferences (cont.) These different thermal preferences act to _________________ with different thermal tolerances during summer stratification. Thereby, the thermal preferences can either enhance or reduce _______________ for other resources depending on whether they __________similar species in more limited areas or separate ____________________. Although in winter, many species move to deeper water, ____________________ due to the much lower levels of activity and feeding associated with reduced _____________________. Wading shorebirds from the west coast of North America Temperature and oxygen gradients can interact to exclude fish from all or a fraction of a water body. ________________________ are a common problem in ________ eutrophic warm water reservoirs and some natural lakes. The hypolimnion initially becomes _________ in summer and the ____________________ gradually rises through the season. Meanwhile, the thermocline is descending (_________________ as surface layer warms). Oxygen-temperature squeeze (cont.) Temperatures in the epilimnion and metalimnion can approach or ____________ limits, while dissolved oxygen falls below usable concentrations (__________) in the hypolimnion. Habitat preferences (cont.) Fish that are vulnerable to predation use a combination of ____________________ to minimize their exposure to _____________ predators. Silversides, Menidia sp., migrate from cover in littoral areas to feed in the _________________ epilimnion offshore at dawn but return to shorelines in the morning before they are ___________. They could fill their stomachs if they remained offshore, but they minimize daylight exposure to offshore __________________. Menidia sp., silversides Similarly, the pelagic juvenile _______________, Oncorhynchus nerka, stay in ______________ water during the day, and ascend to feed for a short period in the zooplankton-rich epilimnion at _____ and dawn. They ascend when light levels are just sufficient to __________________ but dark enough to minimize the probability of detection by _____________. In contrast, the older, less vulnerable kokanee feed _________ in the lighted epilimnion. Reproduction Reproductive strategies consist of reproductive traits that enable fish to leave some ________. Reproductive traits reflect responses to environmental fluctuations. Traits that vary, include: ___________ according to size and age reproductive _____ size of ________ (large eggs---larger larvae-- mouth size, swimming capacity, sensory abilities increase with size reproductive behavior, __________ timing, ___________, the number of times spawning occurs in the life of the female (parity) Age category terminology 1. Age groups represent the number of years a fish ____________ age group 0 = fish in ___________ of life age group 1 = fish in second year of life. 2. ____________: fish born in 1997 are members of the 1997 year class. Fry and fingerling; variously defined, often with different meanings to different people, should not be used unless specifically defined. ____: the time between hatching and the time at which they reach 25 mm in length ____________: fishes between 25 mm and the length at age 1 (Piper et al., 1982). Age category terminology/Aging _________ fishes: newly hatched. Aging methods: scale annuli, circuli, focus ___________ Feeding Fish are often the only important large aquatic predators and results of their __________________ Example: one small fish can eat hundreds more zooplankton than the largest predatory zooplankter. Effect of fish on zooplankton __________________ Feeding may be divided among 1. pelagic fish, which feed in open water _______________ (shad, herring, whitefish, minnows) or piscivorous (mosquito fish, white bass), may also eat ________________ some feed at surface (trout, sunfish) 2. littoral, feed at ___________ 3. benthic, feed on the bottom of lakes and streams. Benthic and littoral feeding is more generalized and can include: grazing on aquatic plants (___________) ingestion of bottom debris (_____________), covered with ______________, protozoans, small insect larvae, and worms ingestion of benthic invertebrates Feeding In _______________, some fish eat _____________________ some pluck insect larvae and crustaceans from the _____________ some feed on _________ in pools some seize ____________ adult insects Resource _______________ Some fish are ____________, while others are very specialized in their selection of food. This resource partitioning means that the fish eat only ______________ of the available food and thus avoid too much _________________ with others. Example: Two species of trout: _______ trout (Salvelus fontinalis) and _________ trout (Oncorhynchus mykiss) brook feed mainly on bottom, taking chironomid and _________________ rainbow, feed near the surface on ____________ organisms in summer Resource partitioning Another example: In streams, the largest, most aggressive carnivores (such as trout) pick off the ________________ above and below __________, or near banks of submerged vegetation. smaller fish, (such as sculpin and dace) catch benthic invertebrates in the _______________ of the riffles suckers ________________ at the bottom of the pools. Mottled sculpin, Cottus bairdi ___________ in flowing waters ____________ or negative, (positive) _____________ (yes or no) negative buoyancy is advantageous for fish that ________________ as _________ tends to hold it in place. many stream and river fish that live and feed on the bottom, _______ or have reduced swimbladders. A fish with neutral buoyancy has no __________ in water. Energy ____________: resting on bottom versus continuous swimming against current (_________) Dace have a swimbladder and continuously swim they use _______________ than if they sat on bottom feed largely on insect larvae taken from the bottom Dace Perhaps they catch more ________ by swimming above the bottom than they could if they crept about on the bottom. In this case ___________ swimming increases a fish’s success in finding food and ___________ the extra metabolic cost of swimming. Many fish that live in fast ________________ are negatively bouyant and they possess _________. ____ may be expanded to form a relatively small sucker around the mouth (Gyrinocheilus) The entire ______________ of the body acts as a sucker (Gastromyzon) both are members of Cyprinidae A fish attached by a sucker depends on friction to ____________________, an extra _________ force is applied by the sucker, increasing the friction. Roanoke hog sucker, Hypentelium roanokense Most _____________ fish feed on algae which encrust the rocks. They collect a large quantity of food from one rock before making a ________________ for another. Stream ecology/fish ___________ Distribution of fish is impacted by water temperature ____________________ and discharge level of _______________ substrate type, sediment load depth, food _____________/abundance etc....later Stream ecology/fish zonation Stream zones have been named for the _______________________ or associations found there. These zones or associations have mainly _______ application. Measurement: ______________________ Fishery studies involve: collection & ______________ of the species present _____ determination growth ______ habitat __________ ___________ structure Collecting/Sampling ______________ Nylon nets: __________, gill nets, _______ nets or _____ nets (for collection of live migrating fish in streams and small rivers) fixed-trap nets with __________ throats which the fish enter but have difficulty exiting. __________ trawls _______________ (streams and shallow regions of lakes) Rotenone (blocks ____________________) _______________ assessment (estimates population abundance, temporal and spatial distribution)