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Brown trout , Salmo trutta. Brook trout , Salvelinus fontinalis. Rainbow trout , Oncorhynchus mykiss. Fry, ~6 wk. Sac fry, alevin, <6 wk. Hatching. Fingerling, 6 mo. Adult 2-3 yr. Fish. Fish dominate the ______________ in most lakes, streams, rivers and estuaries.
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Fry, ~6 wk Sac fry, alevin, <6 wk Hatching Fingerling, 6 mo 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.
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 Cl- through 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 _____________________.
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 __________________.
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.
___________ 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
