Fishless Ponds Research Articles

Morphometry and Cyclomorphosis in Daphnia middendorffiana from a Fishless Pond of the Southern Andes

ABSTRACT The morphology of a population of D. middendorffiana collected during spring and autumn in a fishless pond of the Southern Andes was examined to identify seasonal variations in growth patterns. Body size, tail spine length, width, thickness and biomass were analyzed, and growth was characterized by correlating various morphological dimensions with biomass. A pattern of three growth stages was identified: a juvenile stage characterized by body growth without variation of the tail spine length, a transition stage during which the tail spine experienced a sudden length reduction, and an adult stage with growth patterns similar to the first stage. Specific cyclomorphic growth patterns were found. The dimensions displaying most apparent seasonal differences were tail spine length and body flatness.

Summer distribution patterns of the backswimmer, Anisops wakefieldi (Hemiptera: Notonectidae), in a New Zealand pond

The relative abundance of different‐sized Anisops wakefieldi in a small, fishless pond was determined from sweep‐net samples taken along one open‐water and two shoreline transects at noon on two dates, and at noon and midnight on a third date. During the day, large individuals occurred only along the shore, whereas smaller ones occurred both along the shore and in open water. At night, large individuals also occurred in the open water. The diurnal size‐class segregation suggests that young individuals migrate into less preferred, open water to avoid interference and cannibalism from larger individuals. The shoreline may be preferred during the day because it provides greater food resources or a refuge from visually feeding avian predators. Laboratory experiments in containers with floating aquatic plants at one end complemented the field data. When alone, both small and large A. wakefieldi sought cover during the day and moved into open water at night. During the day, the presence of large individuals induced small ones to move into open water. The results of this study on a notonectid population are consistent with some earlier ones in demonstrating that interactions between large and small size classes may lead to pronounced spatial segregation of size classes, and show for the first time that spatial distributional patterns during the day and night may be very different.

Indirect Monitoring of Agonistic Encounters in Larvae of Lestes viridis (Odonata: Lestidae) Using Exuviae Lamellae Status

Differences in interference competition between larvae of the damselfly Lestes viridis (Vander Linden) were examined using caudal lamellae status of exuviae. Exuviae from a small temporary fishless pond near Antwerp (Belgium) where L.viridis was the only odonate present were studied. No lamellae loss during emergence was seen. Therefore, the lamellae status of the exuviae reflects the lamellae status of the final instar larvae. The deviations of the distribution of the number of missing lamellae per individual from a binomial distribution suggested that lamellae are not always lost separately or that some animals are more prone to agonistic encounters. I found no difference in agonistic encounters between sexes. In accordance with the hypothesis of Pierce et al. (1985) interference competition was higher in the lestid species inhabiting small, temporary fishless ponds than in the coenagrionid damselfly Ischnura posita inhabiting large permanent fish containing water bodies that was studied by Robinson et al. (1991).

LIFE HISTORIES AND THE STRENGTHS OF SPECIES INTERACTIONS: COMBINING MORTALITY, GROWTH, AND FECUNDITY EFFECTS

Interactive effects of one species on another may simultaneously influence mortality, growth, and fecundity. To quantify the strength of an interaction between two species, we must therefore use techniques that integrate these various responses into estimates of overall effect. Demographic models of populations provide such a framework. Here we develop a demographic model describing the life history of a hemimetabolous insect to evaluate the relative importance of predator effects on mortality and growth of damselflies (Enallagma boreale) in fishless ponds and mayflies (Baetis bicaudatus) in trout streams. Previous experiments have shown that dragonfly predators in fishless ponds inflict direct mortality and cause reduced growth rates in Enallagma damselflies. Parameterization of the demographic model from these data show, however, that only the direct mortality effects of dragonflies should significantly influence damselfly population dynamics. This is because damselfly size at emergence does not influence adult female fecundity, so the effects of dragonflies on damselfly larval growth do not influence adult fecundity. Likewise, both trout and stonefly predators inflict mortality on larval Baetis mayflies and cause decreases in growth rates. However, our demographic analyses indicate that the growth effects of both predators should dominate the population-dynamic effects on Baetis. This is because size at emergence translates directly into adult fecundity in mayflies. We also present data suggesting that developmental responses to changes in environmental conditions (e.g., predator abundances, resource availabilities) differ between species depending on these same life history parameters. The biological significance of lethal vs. sublethal predator impacts must be evaluated in a demographic framework to identify whether alterations in growth rate, and the timing of and size at metamorphosis, significantly influence population dynamics. The demographic model used for any particular organism must be tailored to its life history, but the various impacts of interactions with other species can all be integrated into estimates of projected population growth that can then be readily compared among species with different life histories.

Life Histories and the Strengths of Species Interactions: Combining Mortality, Growth, and Fecundity Effects

Interactive effects of one species on another may simultaneously influence mortality, growth, and fecundity. To quantify the strength of an interaction between two species, we must therefore use techniques that integrate these various responses into estimates of overall effect. Demographic models of populations provide such a framework. Here we develop a demographic model describing the life history of a hemimetabolous insect to evaluate the relative importance of predator effects on mortality and growth of damselflies (Enallagma boreale) in fishless ponds and mayflies (Baetis bicaudatus) in trout streams. Previous experiments have shown that dragonfly predators in fishless ponds inflict direct mortality and cause reduced growth rates in Enallagma damselflies. Parameterization of the demographic model from these data show, however, that only the direct mortality effects of dragonflies should significantly influence damselfly population dynamics. This is because damselfly size at emergence does not influence adult female fecundity, so the effects of dragonflies on damselfly larval growth do not influence adult fecundity. Likewise, both trout and stonefly predators inflict mortality on larval Baetis mayflies and cause decreases in growth rates. However, our demographic analyses indicate that the growth effects of both predators should dominate the population-dynamic effects on Baetis. This is because size at emergence translates directly into adult fecundity in mayflies. We also present data suggesting that developmental responses to changes in environmental conditions (e.g., predator abundances, resource availabilities) differ between species depending on these same life history parameters. The biological significance of lethal vs. sublethal predator impacts must be evaluated in a demographic framework to identify whether alterations in growth rate, and the timing of and size at metamorphosis, significantly influence population dynamics. The demographic model used for any particular organism must be tailored to its life history, but the various impacts of interactions with other species can all be integrated into estimates of projected population growth that can then be readily compared among species with different life histories.

Grazing Effects by Green Frog Tadpoles (Rana clamitans) in a Woodland Pond

ABSTRACT I examined whether light availability mediated the extent to which herbivory by green frog tadpoles (Rana chmitans) affected lower trophic levels in a fishless pond in central Kentucky. An enclosure experiment manipulating tadpole presence/absence and light (shaded vs. unshaded) showed that tadpoles can significantly reduce benthic algal biomass in light levels that mimic springtime canopy conditions. Tadpoles, however, had little affect on algal species composition. Grazing did not indirectly affect nutrient (NO3 and PO4) concentrations in experimental treatments, probably because ambient concentrations were beyond growth-limiting levels.

THE CONSEQUENCES OF CHANGING THE TOP PREDATOR IN A FOOD WEB: A COMPARATIVE EXPERIMENTAL APPROACH

Changing the top predator in a food web often results in dramatic changes in species composition at lower trophic levels; many species are extirpated and replaced by new species in the presence of the new top predator. These shifts in species composition also often result in substantial alterations in the strengths of species interactions. However, some species appear to be little affected by these changes that cause species turnover at other positions in the food web. An example of such a difference in species responses is apparent in the distributions of coenagrionid damselflies (Odonata: Zygoptera) among permanent water bodies with and without fish as top predators. Enallagma species segregate between ponds and lakes that do and do not support fish populations, with each lake type having a characteristic Enallagma assemblage. In contrast, species of Ischnura, the sister genus to Enallagma, are common to both fish and fishless ponds and lakes. Previous research has shown that Enallagma species segregate because they are differentially vulnerable to the top predators in each lake type: dragonflies in fishless lakes and fish in fish lakes. This paper reports the results of a series of laboratory and field experiments quantifying the mortality and growth effects of interactions in the food webs surrounding Enallagma and Ischnura species in both lake types. These results are compared to determine how features of the food web change to force segregation of Enallagma species between the lake types but permit Ischnura species to inhabit both. The results of experiments conducted in a fishless lake show that damselflies are not food limited in this lake type, but that they do strongly compete via interference mechanisms. Interference effects between the genera are symmetrical. Ischnura species have substantially higher growth rates than Enallagma species under all conditions in fishless lakes. Although both Enallagma and Ischnura experience substantial mortality from predation by dragonflies (Anax and Aeshna species, the top predators in fishless lakes), these dragonflies display a significant bias towards feeding on Ischnura. Mortality rates due to dragonfly predation are not density dependent. The results of experiments done in a fish lake indicate that damselflies are food limited and thus compete for resources in fish lakes. Ischnura growth rates are also substantially higher than Enallagma species in the fish-lake system. Dragonfly species that coexist with fish (Basiaeschna and Epitheca species) do not impose significant mortality on coexisting damselflies, but they do compete for resources with the damselflies, and they may also generate feeding interference in the damselflies. Fish impose significantly higher mortality on Ischnura species than on coexisting Enallagma species, and this mortality is negatively density dependent. The coexistence of Enallagma and Ischnura species is fostered in both lake types by trade-offs in their abilities to avoid predators and to utilize resources. Native Enallagma species are better at avoiding coexisting predators in each lake type, but these abilities come at the expense of the ability to utilize resources effectively and to avoid the predator found in the other lake type. In contrast, Ischnura are better at utilizing resources in both lake types, but these abilities come at the expense of effectively avoiding both fish and dragonflies. Understanding the trade-offs faced by species at similar trophic positions within a food web is critical to predicting changes in food webs following major environmental perturbations such as changing the top predator.

Experimental Analysis of Trout Effects on Survival, Growth, and Habitat Use of Two Species of Ambystomatid Salamanders

Introduced fish have been implicated as reducing abundance or eliminating ambystomatid salamanders from montane lakes in wester North America. We tested the null hypotheses that survivorship, growth, and refuge use of larvae reared for 30 d did not differ between artificial ponds with trout and without trout Larval survivorship for both A. macrodactylum and A. gracile was significantly lower in ponds with trout than in fishless ponds. Both species had significantly lower snout-vent lengths in ponds with trout than in fishless ponds at the conclusion of the experiments. Only A. gracile had significantly lower body weight in ponds with trout than in ponds without trout For both species, substrate locations of larvae were significantly influenced by trout at the conclusion of the experiments. Larvae of both species were found in a narrower range of substrates in ponds with fish than in control ponds. Our findings support inferences from field studies that the presence of trout have negative impacts on larval A. macrodactylum and A. gracile.

屋外実験池を用いたラン藻類優占に及ぼす魚の影響に関する研究

Experiments using six outdoor experimental ponds equipped with a continuous flow-through system of the same influx nitrogen and phosphorus concentrations and with different fish (goldfish) densities were conducted from Aug., 1993 to Sep., 1994 to investigate the factors influencing the dominance of blue-green algae in summer. In general, blue-green algae predominated in fish ponds, in contrast to green algae in fishless ponds. Blue-green algae started to flourish after the latter half of August, when the PO4-P concentrations decreased to less than 10 μg·l-1. The difference in dominated phytoplankton between fish and fishless ponds could be explained by the reduction of total phosphorus and subsequently the depletion of PO4-P in pond water due to the feces of fish and their growth, the condition of which is advantageous for blue-green algae than others.

Changes in the structure of a zooplankton community during a Ceratium (dinoflagellate) bloom in a eutrophic fishless pond

The community structure of zooplankton was studied in a eutrophic, fishless Japanese pond. The ecosystem was dominated by a dinoflagellate, Ceratium hirundinella , two filter-feeding clado-cerans, Daphnia rosea and Ceriodaphnia reticulata , and an invertebrate predator, the dipteran Chaoborus flavicans . The midsummer zooplankton community showed a large change in species composition (the Daphnia population crashed) when a heavy Ceratium bloom occurred. It is shown that (i) the rapid density decline of D.rosea in mid-May was mainly caused by a shortage of edible phytoplankton, which was facilitated by the rapid increase in Chirundinella abundance; (ii) the low density of D.rosea in June-July was considered to be mainly caused by the blooming of Ceratium hirundinella (which may inhibit the feeding process of D.rosea), while predation by Cflavicans larvae, the changing temperature, the interspecific competition and the scarcity of edible algae were not judged to be important; (iii) the high summer biomass of the planktonic Cflavicans larvae was maintained by the bloom of C.hirundinella, because >90% of the crop contents of C.flavicans larvae were C.hirundinella during this period. The present study indicates that the large-sized cells or colonies of phytoplankton are not only inedible by most cladocerans, but the selective effect of the blooming of these algae can also influence the composition and dominance of the zooplankton community, especially for the filter-feeding Cladocera, in a similar way as the selective predation by planktivorous fish. The large-sized phytoplankton can also be an important alternative food for ominivorous invertebrate predators such as Chaoborus larvae, and thus may affect the interactions between these predators and their zooplanktonic prey. In this way, such phytoplankton may play a very important role in regulating the dynamics of the aquatic food web, and become a driving force in shaping the community structure of zooplankton.

Effects of aquatic insect predators on zooplankton in fishless ponds

We removed the surface-orienting aquatic insects from a fishless pond to determine their predation effects on zooplankton behavior and size structure. A second fishless pond served as the unmanipulated reference system in this two year study. In the reference pond and the treatment pond prior to manipulation, daphnids exhibited pronounced diel vertical migrations. Following the removal of surface-orienting aquatic insects from the treatment pond, daphnid migration changed to a reverse migration strategy that was significantly different from that observed in the reference system. Average daphnid body size increased significantly following predator removal in the treatment system. Our data indicate that predation by aquatic insect predators, such as notonectids and dytiscids, may affect daphnid migration behavior in fishless systems. Vertical migration by daphnids may allow coexistence with surface-orienting insects in ponds that are deep enough to provide a spatial refuge from these predators.

Predator Community Composition and Patterns of Variation in Life History and Morphology Among Hyalella (Amphipoda) Populations in Southeast Michigan

-The amphipod, Hyalella azteca, is found in an ecologically diverse array of permanent freshwater habitats, including lakes with predatory fish and fishless ponds and marshes. To determine the extent to which Hyalella populations vary among habitats and the degree of covariation between predator community composition and Hyalella traits, I examined morphological and life history traits of adult individuals collected from nine diverse habitats in SE Michigan. Two distinct Hyalella morphotypes were apparent in the samples. A small-bodied morphotype had smaller adult body size, smaller size at first reproduction, and smaller eggs than a second, large-bodied morphotype. For morphological traits other than size, differences between morphotypes were less clear, with small but significant differences found in one sex only in antennal segment number and dorsal spine length and no differences between morphotypes in gnathopod width. Morphotype was consistently associated with habitat type. In general, fishless habitats and habitats in which sticklebacks (Culaea inconstans) are dominant fish predators contained only individuals of the largebodied morphotype, whereas habitats with well-developed centrarchid fish communities contained only individuals of the small-bodied morphotype. I suggest that the regime of sizebiased predation experienced by Hyalella in each habitat may be the primary determinant of the pattern of association between Hyalella morphotype and habitat type. Morphotypes co-occur in a single habitat, probably because the unusual character of this water body provides extensive regions that are suitable for each morphotype.

Trophic Control of Fishless Ponds by Tiger Salamander Larvae

We examined the extent to which predation by larval tiger salamanders (Ambystoma tigrinum nebulosum) affected lower trophic levels in fishless ponds in montane eastcentral Arizona. An enclosure experiment manipulating salamander densities showed that effects associated with larval presence can cascade downward through three trophic levels in environments of low complexity. Enclosures with larvae contained comparatively lower herbivorous zooplankton biomasses and densities, higher chlorophyll a concentrations, and lower orthophosphate levels than those without larvae. Relative frequency of zooplankton species also varied significantly among enclosure treatments. Cyclopoid copepod frequencies were higher in treatments with salamanders than without, while ostracods were found only in treatments without salamanders. Salamander presence negatively affected cladoceran abundance and influenced cladoceran species composition. Proportions of both Ceriodaphnia quadrangula and Simocephalus vetulus were significantly greater in treatments without salamanders than in treatments with salamanders. Although Daphnia pulex frequencies were similar in enclosures with cladocerans across treatments, individuals were on average larger and biomasses were greater in enclosures without salamanders than they were in enclosures with salamanders. Trophic interactions analyzed from our survey of 14 ponds, however, were most often uncorrelated, and the few top-down effects exerted by salamanders were limited to contiguous trophic links below them. Densities of only one zooplankter, ostracods, and two taxa of macroinvertebrates, Baetis spp. mayflies and odonate larvae, were negatively related to salamander density. In contrast, benthic chironomid densities correlated positively with salamander density. However, in the two salamander-free ponds surveyed, we observed a distinct pattern of alternating responses of trophic levels that paralleled those in enclosure treatments without salamanders. Although modulating factors operate in ponds to complicate salamander impacts, salamanders have discernible direct and indirect effects on pond trophic webs.

Size-Biased Predation and Prey Life Histories: A Comparative Study of Freshwater Amphipod Populations

A prior survey of Michigan populations of a freshwater amphipod, Hyalella azteca, indicted that populations occur as one of two morphotypes that differ in body size and life history traits. Population types, which may represent separate species, are associated with distinct habitat types. Generally, lakes with centrarchid fish contain a small—bodied form, and fishless ponds and marshes contain a large—bodied form. In this comparative study of two Hyalella populations, I examine the potential role of size—biased feeding by major predators in maintaining, and perhaps generating, the pattern of association between Hyalella morphotype and habitat type. In Duck Lake (Centrarchid fish present), overall mortality generally increased with body size in each of two study years, and adult mortality exceeded juvenile mortality. The opposite pattern was observed in a nearby fishless habitat, Duck Marsh, where mortality generally declined with size, so that juvenile mortality exceeded adult mortality. To determine the degree to which size—biased predation might cause the observed mortality patterns, I used stomach content analysis to assess prey size preferences of fish in the lake habitat and laboratory foraging trials to examine size—biased predation by invertebrate predators from the marsh. Fish predators displayed a strong tendency to prey on larger, adult Hyalella. Size preferences exhibited by larval dragonflies, the principal invertebrate predators in the marsh habitat, depended on predator body size, with small larvae preferring juvenile Hyalella and the largest larvae preferring adults. In general, size—selective predation by major predators in each habitat appeared to contribute importantly to overall mortality patterns, the exception being the marsh habitat in a year of low predator density. Observed differences in life history traits between populations are in close agreement with predictions derived from life history models addressing the influence of size—biased mortality on the evolution of reproductive allocation, size at maturity, and egg size. Life history characteristics of Hyalella were measured both on field—collected individuals and on individuals reared for approximately two generations in replicated predator—free artificial ponds. In field samples, the lake Hyalella population exhibited a smaller mean adult body size, smaller size at maturity, smaller egg size, and higher size—specific fecundity and reproductive investment that the marsh population. These life history differences were also observed in the artificial pond experiment, indicating that these traits are genetically based and nonplastic.

Growth, Density, and Interspecific Influences on Pumpkinseed Sunfish Life Histories

I collected data on 27 pumpkinseed (Lepomis gibbosus) populations in eastern and central Ontario and conducted a transplant experiment with one of these populations to test growth and competition—related predictions of several life history models. The predictions are that early maturity and high gonadal investment will occur: (1) in large and fast—growing juveniles; (2) in populations with low adult: juvenile growth ratios; (3) in populations with low density; and (4) in the absence of bluegill sunfish (Lepomis macrochirus), a competing congener. Predictions 1 and 4 were fully supported and Prediction 2 was partly supported, but Prediction 3 was not. The earliest maturing juveniles within populations were significantly larger than conspecifics of the same age that did not mature. Females from a lake population that were transplanted into a fishless pond exhibited both significantly faster growth and a significantly higher gonad to body mass ratio (gonado—stomatic index) that females living in the lake. At the population level, juvenile growth was significantly correlated with age at maturity (r = 0.52), but not with gonadostomatic index, whereas the Adult : Juvenile Growth Ratio showed a significant, negative correlation wih gonadosomatic index (r = 0.66), but not with mean age at maturity. Mean age at maturity showed a stronger correlation with the indicator of life—span and adult survival rate (r = 0.74), suggesting that mortality is more important than growth in the shaping of reproductive life histories of pumkinseed. High population density was associated with early maturity and high gonadal investment, the opposite of what was predicted. However, pumpkinseed populations that co—occurred with bluegills did mature significantly later and at a larger size and tended to have a lower gonadal investment than populations living in waterbodies without bluegills. This difference in reproductive patterns in the presence of bluegill is consistent with two—stage life history theory and may be the result of a direct effect of bluegills on pumpkinseed growth and survivorship, as well as differences in environmental conditions were the two species do or not co—occur.

The Response of Naive Breeding Adults of the Spotted Salamander To Fish

Several recent investigations have shown that somc species of salamanders are capable of perceiving the presence of fish in breeding ponds through olfaction. It has been suggested that breeding adult salamanders may avoid depositing eggs in pools containing fish. We examined the hypothesis that breeding salamanders avoid fish ponds through olfactory cues in two field tests. In the first, naive spotted salamanders (Ambystoma maculatum) restrained within screened enclosures were submerged in either fish or fishless ponds. The number of eggs laid within each enclosure was counted at the conclusion of breeding. There was no difference in the number of eggs within and among four fishless and three fish ponds. In the fourth fish pond the fish harassed the salamanders and completely inhibited reproduction. We repeated the experiment using double screened enclosures in which the salamanders were free from direct fish attack but were still exposed to fish scent. There was no difference in egg production. The second test repeated the design of the first but provided the salamanders with the choice of remaining in the double screened enclosures or exiting the pond. The test animals from both the fish and fishless ponds responded similarly in their breeding activities. We conclude that naive spotted salamanders do not avoid fish ponds based solely on olfactory cues.

Plasticity of Daphnia Life Histories in Response to Chemical Cues from Predators

The possible induction of life-history shifts in prey by chemicals released into the environment by potential predators was examined. Laboratory life-table experiments were conducted to examine the influence of chemical substances released from vertebrate (fish) and invertebrate (Notonectidae) predators on life-history features of two clones (B―coexists with fish, W―from a fishless pond) of the freshwater cladoceran crustacean, Daphnia magna. Significant differences between treatments in key life-history features (i.e. size and age at first reproduction) were detected for each clone. Both clones showed a significantly smaller size at first reproduction when raised under fish-treated water, when compared with animals raised under invertebrate-treated water

Effect of Nile Tilapia (Oreochromis niloticus) on the Ecosystem of Aquaculture Ponds, and Its Significance to the Trophic Cascade Hypothesis

The trophic cascade hypothesis holds that an increase in fish biomass causes a decline in food organisms of the fish, which cascades down to regulate lower trophic levels by altered consumptive demands. This hypothesis was evaluated by stocking Nile tilapia (Oreochromis niloticus) at densities of 0, 1, 2, or 3 fish/m3 in triplicated 220-m3 ponds near Bangkok, Thailand. All ponds were fertilized with 500 kg chicken manure∙ha−1∙wk−1. We measured phosphorus, nitrogen, chlorophyll a, primary productivity, zooplankton abundance, and fish yield in all ponds. Increased stocking density resulted in decreased adult fish growth but similar yields among the three density treatments. Regressions relating the abundance of each trophic level to the next higher trophic level were either positive or nonsignificant, which is contrary to trophic cascade predictions. Zooplankton became significantly more dense over time in fishless ponds than the other three treatments, but no other trophic level differed among treatments. These results indicate that presence of fish had a significant effect on zooplankton in ponds, but biomass of fish or abundance of zooplankton did not significantly affect other trophic levels.

A Field Test for the Cues of Disapause in a Freshwater Copepod

The freshwater calanoid copepod Diaptomus sanguineus switches each year in spring from making eggs that hatch immediately to making diapausing eggs that rest in lake sediments for an extended period. In lakes and ponds containing planktivorous fish, the timing of the switch is highly consistent between years and comes at the theoretically optimal time (late March) to avoid intense summer predation. In fishless ponds the timing comes 1—2 mo later. We investigate here the environmental cues used by the copepods to time the switch to diapause. Through the use of both field and laboratory manipulations, we show that temperature and photoperiod play central roles as diapause stimuli. A field manipulation of fish density failed to reveal either a direct induction of diapause or any more subtle effects of fish occurrence on diapause timing. The copepods made immediately hatching eggs under short—day or low—temperature conditions, and diapausing eggs under long days or high temperatures. There appears to be variation between individuals in their responses to temperature and photoperiod so that similar diapause phenologies are produced by different sensitivities to the environmental cues.

Effect of Golden Shiners on Plankton and Water Quality in Ponds Managed for Intensive Production

AbstractWater quality variables and plankton were monitored and compared between ponds that were stocked or not stocked with golden shiners in order to determine what changes occur in the plankton community and water quality of ponds managed for intensive production. Ponds with shiners had significantly lower phosphate and carbon dioxide concentrations and lower carbonate alkalinity than ponds without shiners. No significant difference in nitrite, nitrate, ammonia, temperature, secchi disk readings, or turbidity levels was found between the treatments. The standing crop of phytoplankton was nearly twice as great in ponds with fish. Ponds with fish had significantly fewer copepods but more rotifers than fishless ponds. Although the fish were offered a commercial feed with 29.5% protein and 1.5% crude fat at 3% of their biomass daily, they apparently continued to feed on crustacean zooplankton.