Fish Of Different Sizes Research Articles

Factors Affecting the Diet of Crested Terns, Sterna-Bergii

For crested terns, Sterna bergii Lichtenstein, changes in the accessibility of prey may cause changes in the composition of the terns' diet during the course of the tidal cycle, or in where and when the terns hunt. Some active selection of prey may also occur, for the terns feed fish of different sizes to chicks of different ages. Furthermore, some adults may hunt in specific places at specific times since many of the prey species are site-specific and are accessible only at certain times during the tidal cycle. More skill may be required to catch prey species that dwell on the bottom or in mid-water than those that dwell at or near the surface. We did not find a strongly consistent pattern in the times at which the terns feed their chicks, which may reflect the terns' opportunistic foraging habits.

Optimal Intra- and Interseasonal Harvesting Strategies when Price Varies with Individual Size

A major concept in fisheries management is the optimal age for first capture. Because there can be separate market categories for fish of different sizes and different costs for their harvest, a more rational statement of the problem would be to find the optimal range of harvest sizes in any given year. Two models for solving this problem are presented. The shrimp model discusses optimal harvest of a single cohort of shrimp as it grows through a season. The lobster model discusses optimal simultaneous harvest of several cohorts over several seasons. The difficulty of defining a cost per fish in the lobster model makes it a much more complex undertaking.

Size Selectivity and Bias in Estimates of Population Statistics of Smallmouth Bass, Walleye, and Northern Squawfish in a Columbia River Reservoir

Abstract We describe size selectivity of five types of gear, size selectivity in combined gear samples, and potential bias in estimates of population statistics of smallmouth bass Micropterus dolomieui, walleye Stizostedion vitreum, and northern squawfish Ptychocheilus oregonensis in John Day Reservoir on the Columbia River. We sampled from 1983 to 1986 with two types of gill nets, boat electrofishers, trap nets, and rod and reel. Different gears selectively sampled different sizes of each species. Recapture rates indicated that different sizes of fish remained differentially vulnerable to capture even when samples from all gears were pooled. Vulnerability of smallmouth bass declined with increasing size. Vulnerability of walleye was not related to size. Vulnerability of northern squawfish increased with size. Size selectivity of gear resulted in estimates of abundance potentially biased by 2–16%, estimates of proportional stock density (size structure) biased by 11–46%, and estimates of annual rate of mo...

Selectivity of hooks in the handline fishery of the Saya de Malha banks (Indian Ocean)

Experimental handline fishing trials were conducted on the coral-reefs of the Saya de Malha banks with different hooks within a size range difference of 96% between the biggest and the smallest ones. The major species of fish captured was Lethrinus mahsena representing about 90% of the total catch. For a given population, no effect of modifying the size of tooks and baits on selectivity under varying fishing conditions was identified. The relative abundance of larger fish catch, however, obtained in preference to smaller fish indicates the existence of competition among fish of different sizes.

Visual detection by the rod system in goldfish of different sizes

New rods are continually generated and inserted across the entire differentiated retina in juvenile and adult goldfish; no other retinal cells share this characteristic. How does the preferential addition of rods affect visual function? To examine the relation between continued rod addition and visual sensitivity, we measured absolute threshold in fish of different sizes. Twenty-nine fish were trained in a classical conditioning paradigm and psychometric functions were obtained for each of them for detection of a 532 nm light 5 sec in duration, 140 deg in angular subtense, presented while the fish was fully dark adapted. We found that absolute threshold (expressed in terms of retinal photon density) was lower in larger fish, but by a very small amount: on average, large fish (15.4 ± 0.5 cm standard body length) were 1.45 times more sensitive than small fish (4.3 ± 0.3 cm). Morphometric analysis showed that the planimetric density of rods in goldfish retina increases at a similar rate between small and large fish, while the density of retinal ganglion cells declines between small and large fish (by a factor of 3.8). The ratio of rods to ganglion cells (a possible indicator of neural convergence) increased, but by a factor that is too large to reconcile with the psychophysical results (5.3 ×). The results suggest that absolute visual threshold in the goldfish is closely related to the density of rods in the retina.

Comparison of trace metal concentrations in muscle tissue of a benthopelagic fish ( Coryphaenoides armatus) from the Atlantic and Pacific oceans

Specimens of Coryphaenoides armatus, a benthopelagic fish, were collected from the North Atlantic and North Pacific for trace metal analysis. Concentrations of cadmium and lead in muscle tissue of Atlantic fish were not significantly different from those of Pacific fish. Differences in copper concentrations in the two groups may be related to size difference. Higher concentrations of nickel, cobalt, iron and manganese observed in muscle tissue from the Pacific fish may be due to differences in fish size and differences in deep water metal chemistry between the two oceans.

Sex and Year Comparisons of Lake Superior Pink Salmon ( Oncorhynchus Gorbuscha) Adipose Fins

The adipose fins of pink salmon ( Oncorhynchus gorbuscha Walbaum) from the Carp River, a southeastern Lake Superior tributary, are sexually dimorphic. The adipose fins of males are consistently longer than those of females for all sizes of fish measured, despite sex and year differences in fish size. Greater relative adipose fin size in males may help reduce caudal peduncle wear resulting from agonistic interactions among competing males on the spawning grounds. Differences in relative adipose fin size between years were not found, consistent with the lack of segregation between even- and odd-year stocks which characterizes Great Lakes populations. Adipose fin size increased in a positive allometric fashion with increasing fish length in both sexes. Compared to British Columbia pink salmon, adipose fin sizes are less distinct sexually but similarly variable. This finding holds promise for use as a technique for sexing older Great Lakes pinks externally, and hence may have management implications.

Stomach contents of the Antarctic Silverfish Pleuragramma antarcticum from the southern and eastern Weddell Sea (Antarctica)

The stomach contents of 142 Pleuragramma antarcticum from the southernmost part of the Weddell Sea (Gould Bay: 77°19′S) and from the eastern coast (72°–74°S) were analyzed. The fish were collected in February 1983 and stored frozen. Size range of the investigated specimens was from 6.4 cm SL (7.3 cm TL) to 21.9 cm SL (24.1 cm TL). The fish were caught by bottom trawl (Gould Bay) and Agassiz Trawl and pelagic RMT-m net in the upper 300 m layer at the eastern coast, respectively. Thirty-six stomachs were empty or contained sand only. The most important prey in terms of biomass were euphausiids, which occurred in 49 stomachs at a mean number of 2. Their dry weight was estimated to be 15–50 times that of the next important food items, which were copepods, gastropods and gammarids. Krill (Euphausia superba) constituted up to 14% of the euphausiids in the diet of fish caught in the eastern Weddell Sea. The rest was usually made up by Euphausia crystallorophias. This species was taken with preference even when the abundance of E. superba in accompanying plankton catches was 16 times higher. In the Gould Bay, gastropods were frequently eaten despite high numbers of copepods in the plankton, whereas in the eastern Weddell Sea, copepods were abundant both in plankton and in the stomach content. The almost complete absence of the early stages of fish in the diet of Pleuragramma antarcticum in the southern and eastern Weddell Sea is due to a pronounced vertical segregation of fish of different sizes. This distribution pattern is thought to be an adaptive mechanism to avoid intraspecific predation, as 90% of the ichthyoplankton in that area is Pleuragramma antarcticum.

The assessment of flow characteristics at certain weirs in relation to the upstream movement of migratory salmonids

A major problem in relation to the rehabilitation of migratory salmonids into many industrial rivers in South Wales is the presence of large abstraction weirs which can, under certain flows, constrain the upstream migration of fish. A method is presented whereby the constraints at two weirs on the River Afan were assessed by relating the swimming capacities of different sizes of fish and the flows needed to stimulate upstream movement to the distribution of flows and current velocities. The ‘gateways’ for fish to ascend the weir are calculated, and their significance in relation to historical flow data and the requirement for remedial action are assessed.

Trophic Resource Allocation between Percina sciera and P. ouachitae in the Tombigbee River, Mississippi

Aspects of the trophic ecology of Percina sciera and P. ouachitae from a site on the Tombigbee River, Mississippi, were compared to: (1) determine the extent of seasonal, sexual and size class trophic allocation in the two species; (2) describe the feeding habits of the two species and compare these habits to a syntopic group of benthic fishes, and (3) determine whether a relationship exists between predator morphology and prey characteristics. The two species had similar diets which corresponded closely to diets for darters of similar habitats. There were small qualitative differences in diet, and gut content changed seasonally in both species. Percina sciera took larger prey than P. ouachitae in the autumn, and this was related to differences in fish size (standard length). Males and females differed in prey size selectivity and the differences were greatest in the spring. With the exception of standard length, no morphological trait of the two species was highly correlated with prey size. Trophic competition is likely of minor importance between these species. INTRODUCTION One means by which species of similar habits may coexist is by allocation of trophic resources (Schoener, 1974a). The gut contents of sympatric fishes of similar feeding habits may differ in prey kind (e.g., Hartley, 1948; Keast, 1966; Mathur, 1972), actual prey length (e.g., Northcote, 1954; Tyler, 1972; Ross, 1977; Yoshiyama, 1980); and prey may be selected on the basis of prey size (O'Brien et al., 1976) or prey evasiveness (Vinyard, 1980). Trophic resource partitioning may also be effected by ontogenetic use patterns (Ross, 1978; Nakashima and Leggett, 1978; Fahy, 1980). Limiting morphological similarity relating to the trophic function of the species within the community may also be important (Hartman, 1958; Werner, 1974; Montgomery, 1977; Smartt, 1978; Gatz, 1979b; Ricklefs and Travis, 1980). Studies of resource partitioning are best carried out on functional groups of species, or guilds (Root, 1967; Krebs, 1978), which exploit a common resource base in a similar way and in which competition is expected to be greatest. Comparative studies of the trophic ecology among guilds of fishes are common (e.g., Hartley, 1948; Northcote, 1954; Keast and Webb, 1966; Keast, 1966, 1978; Thomerson and Wooldridge, 1970; Tyler, 1972; Ross, 1977; Yoshiyama, 1980). However, even though the feeding habits of benthic stream fishes have been studied (e.g., Scalet, 1972; Page and Smith, 1970; Page, 1974; Schenck and Whiteside, 1977; Burr and Page, 1978), fewer studies are available which directly compare the food habits of closely related darters (Percidae). Cordes and Page (1980) compared aspects of the trophic ecology of Etheostoma zonale and E. microperca in Illinois. Adamson and Wissing (1977) observed the diets of E. careruleum, E. flabellare and E. zonale in an Ohio stream. Daiber (1956) compared the food habits of the darter E. flabellare with Cottus bairdi in New York, and Thomas (1970) examined diets of four species of darters in Illinois. This study describes aspects of the trophic ecology of two ecologically and morphologically similar darters, Percina sciera and P. ouachitae, from the Tombigbee River in Mississippi. I compare diet complement, prey size and volume and the morphology of trophic structures, as well as seasonal, size class and sexual differences in diet. I evaluate one assumption of the ecomorphological model (Gatz, 1979a) by comparing 'Present address: Department of Entomology, Mississippi Entomological Museum, Drawer EM, Mississippi State, Miss. 39762.

Growth studies with fish—overcoming the problems of size variation

The relationship between growth rate and fish size is described by the equation logeGw=a—0·4 loge W, where Gw is the specific growth rate and W is fish weight. Since the intercept (a) represents the loge Gw of a fish unit size, the relationship presents a method allowing comparison of data from experiments involving fish of different sizes. The application of the method is demonstrated by examining the effects of environmental temperature on growth rates of cod, Gadus morhua, and it is suggested that the optimum temperature for growth of cod is 13–15° C.

The effect of feeding thyroid hormones on saltwater tolerance and growth rate of Atlantic salmon

Two experiments, involving the addition of thyroid hormones to the diet of salmon parr (Salmo salar) were carried out. The prime purpose of these experiments was to study the effect of feeding thyroid hormones on saltwater tolerance. Saltwater tolerance is interrelated with size and therefore growth rate was investigated. In experiment I three different thyroid preparations were used: thyroid extract, 3,5,3′-triiodo-L-thyronine (T3), and thyroxine (T4). Each thyroid preparation was fed to two different sizes of fish with two different concentrations in the diet. T3 gave the best overall results, both for saltwater tolerance and growth rate. No interaction was found between fish size and concentration of thyroid hormone in the diet. In experiment II three different concentrations of T3 in the diet were fed to salmon parr of two different ages. Feeding T3 improved saltwater tolerance and growth rate of 7-month-old fish but had a negative effect upon growth for 19-month-old fish. For the 7-month-old fish 10 mg T3/kg dry food gave the best effect on saltwater tolerance, while 1 mg T3/kg dry food was enough to improve growth. It is concluded that it is possible to induce smoltification in underyearling Atlantic salmon out of season by feeding thyroid hormones.

Timing and Relative Intensity of Size-Selective Mortality of Juvenile Chum Salmon (Oncorhynchus keta) During Early Sea Life

Available evidence indicates that mortality of juvenile salmon during early sea life is high and probably size dependent. I used scale analysis to determine the timing and relative intensity of size-selective mortality in chum salmon (Oncorhynchus keta) during early sea life. Significant size-selective mortality could be demonstrated only over the time period that the fish were laying down circuli 2–4 on their scales. The relative intensity of mortality for different sizes of fish suggested that mortality was strongly size selective over the size range 45–55 mm fork length. No particular mortality agent could be identified, but the size range involved corresponds with the size at which chum salmon move from very shallow water and nearshore habitat to open water pelagic habitat.Key words: size-selective mortality, salmon, early sea life

Effects of water hardness and pH on vanadium lethality to rainbow trout

Seven-day LC 50s of vanadium pentoxide for 2.5-g trout showed only a small range, from 1.9 to 6.0 mg V I −1, in tests at all 12 combinations of 30, 100 and 355 mg 1 −2 total hardness with pH 5.5, 6.6, 7.7 and 8.8. Toxicity decreased from low to high hardness by an average factor of 1.8, probably because of regulated vanadium intake at the gill membranes. Hardness did not exert a major effect, probably because vanadium is present in water as various anions and does not complex with carbonates and bicarbonates as do most metals which behave as cations. Toxicity was greatest at pH 7.7, and the predominating ion H 2VO − 4 was apparently the most toxic one. HVO 2− 4 which prevailed at high pH, was calculated to be 60% as toxic as H 2VO − 4. Toxicity decreased at pH 6.6 and 5.5, probably because much of the metal was then present as decavanadates, which were found to be half as toxic as H 2VO − 4 on the basis of vanadium content. Small fish were more resistant to vanadium than larger ones, at least up to 12 g wet wt. However cumulative mortality continued to increase until 2 weeks of exposure, and incipient lethal levels were probably much the same for fish of different size, at about 60–70% of the 7-d LC 50s stated in the paper. The toxicity of vanadium is similar to that of zinc except that it does not show a major change with water hardness.

Improved rotatory-flow technique applied to Cod ( Gadus morrhua L.)

An improved version of rotatory-flow apparatus is described, allowing tests of fitness with fish of different size at constant temperature. Cod ( Gadus morrhua, L.) was used as experimental animal, and its treatment and behaviour during different phases of the test are described in some detail. Each test results in determination of the “critical rev min −1” at which the fish is just brought to rotate with the water. The mean of a series of 10 critical rev min −1 with the same fish, multiplied by the interior circumference of the rotational tube used, gives the “critical peripheral velocity” of the specimen. Critical peripheral velocities of a sample of fish, plotted against the standard length of the fish, arrange themselves along a straight line which intersects the vertical axis near the origin. Divided by the corresponding standard lengths the critical peripheral velocities give “reaction quotients”, the mean of which describe the reaction of the whole sample of fish. Optimal experimental conditions have been found by investigating the effects of systematic variation in streaming velocity, relationship between rotational tube diameter and fin-breadth, temperature, and effects of repetition of test-series on successive days etc. on the results of testing.

The Fish Size, Prey Size, Handling Time Relation in Several Sunfishes and Some Implications

The relation between fish size, prey size, and handling time was determined for bluegill (Lepomis macrochirus) and green (L. cyanellus) sunfishes with both artificial and natural prey. When scaled by plotting handling time against the ratio of prey size to mouth size, the relation was quite general across fish size and species and is described by a modified exponential equation. Handling time increases [Formula: see text] fold as fish approach satiation. Curves of handling time/unit return define optimal prey size for fish of different size and/or species and illustrate comparative aspects of the breadth of diet for different sized sunfish. Certain life history features of the bluegill are interpreted on the basis of these curves. Optimal prey size occurs at a prey size to mouth size ratio of 0.59 regardless of fish size.

The Effects of Angling and Hatchery Trout on the Abundance of Juvenile Steelhead Trout

We assessed the effects of angling and planted trout on the abundance of wild juvenile steelhead trout in a rearing stream with underwater censusing of abundance and angling for steelhead in sections with and without planted trout. A large proportion of the juvenile steelhead were removed by angling. The presence of hatchery reared, catchable-size rainbow trout did not affect the angling harvest of juvenile steelhead trout. Angling reduced the abundance of juvenile steelhead in the catch-remove study sections but did not alter the numbers of juvenile steelhead in catch-release study sections. Partial recolonization of fished-out areas occurred. Angling was selective for larger juvenile steelhead in the test sections, but had no detectable effect on the average size of fish in subsequent samples because fished-out areas were recolonized by fish of the same size as those originally removed. Differences in fish size and habitat preferences reduced interactions between hatchery rainbow trout and juvenile steelhead trout. Hatchery trout released into study sections slightly altered the distribution of juvenile steelhead trout.

Under-water sounds of the Japanese gurnard Chelidonichthys kumu

The sound-producing mechanism of Chelidonichthys kumu (Lesson and Garnot) is described. Descriptions are also given of sounds produced among groups of fish of different sizes, as well as the sound of each individual in the group. Sound patterns and peaks of dominant frequency do not change with size of the fish or of its swim-bladder. The dominant frequency range varies slightly in fish of very different sizes.

Food Habits of the Otter Lutra lutra L. and the Mink Mustela vison Schreber in a Trout Water in Southern Sweden

The feeding habits of otter and mink were studied in a trout water in southern Sweden in 1966-68. 350 otter scats and 122 mink scats, collected from all the seasons, were analysed. The fish fauna was studied by means of electrofishing. The food of the two predators greatly overlapped (60-70% approximately) as they both exploited easily available prey. The otter fed for most of the year almost exclusively on fish (frequency analysis indicated 90.8 % of food). The mink fed not only upon fish but also upon water-fowl and mammals, mainly small rodents (24.4% and 9.5% respectively of food). The corresponding figures for the otter were 5.5 % and 0.2 %. The two predators tended to feed upon fish of different sizes. About 30% of the fish taken by otter exceeded the maximum size of fish

Species Associations of Benthic Fishes on the Continental Shelf and Slope off Oregon

Four species associations of benthic fishes found off the coast of Oregon within the depth interval from 40 to 1829 m were characterized by two or three most abundant species, depth range, and average sediment type.Little overlap was found among species associations because many species had maximum abundance or were found only in one association. When a species occurred in more than one association, different sizes of fish were often found. Species on the lower continental slope had the broadest depth range, and a few species were found only in the deepest association.Sixty-seven species of bottom fishes representing 21 families were collected, but 86% of the total number of fishes were from the families Pleuronectidae, Scorpaenidae, and Bothidae.