Functional response of Ameca splendens (Family Goodeidae) fed cladocerans during the early larval stage

We studied the functional response of the goodeid Ameca splendens , an endangered species from rivers Ameca and Teuchitlán (Jalisco, Mexico), from birth until 8 weeks old. The cladocerans, Alona glabra adults, Simocephalus vetulus neonates, Ceriodaphnia dubia adults, Daphnia pulex juveniles and Moina macrocopa adults were used as prey. The prey densities, depending on the species, ranged between 0.25, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 16.0 and 32 ind. mL⁻¹, with four replicates at each density. We found that all functional responses were Type II. During the feeding period of 30 min, the fish larvae consumed about 600 individuals of the smallest prey A. glabra (450 μm). The consumption of larger prey (<1.0 mm) such as S. vetulus, C. dubia, D. pulex and M. macrocopa ranged between 150 and 200 prey larva⁻¹ during the feeding trials. Our study shows that A. splendens reached maximal prey consumption at around 4 weeks of age, after which there was no increase in prey consumption during the feeding period with age until the end of the study period of 8 weeks. Our study indicates that prey digestion rather than handling time determines the functional response in this fish species and that M. macrocopa is most suited as live food for A. splendens .     

Strategies for Development of Rotifers as Larval Fish Food in Ponds

Strategies to sustain rotifer peak biomass, distribution of rotifer resting eggs in the sediment, and relationship between rotifers and larval fish growth were studied in a series of pond experiments. After the ponds were filled with water, herbivorous rotifers (e.g., Brachionus calyciflorus ) developed first, but were gradually replaced by predatory rotifers (e.g., Asplanchna ). Subsequently, herbivorous cladocerans (e.g., Moina sp) eventually replaced rotifers and dominated the zooplankton community. The occurrence of Asplanchna and Moina indicated the decline of B. calyciflorus . Peak rotifer biomass developed 8–10 d after the ponds were filled with water at 20–25 C, 10–15 d at 17–20 C, 15–20 d at 15–17 C, 20–30 d at 10–15 C, and >30 d at < 10 C. The abundance of resting eggs in the top 5-cm sediment varied from 6 to 83/cm². About 25% of resting eggs were buried in the top 5-cm sediment but the number of resting eggs decreased with increased sediment depth. Optimum rotifer biomass for silver carp Hypophthalmichthys molitrix larvae stocked at 1,500,000/ha was 20–40 m/gL. High rotifer biomass (>20 mg/L) usually lasted 3–5 d, but could be prolonged by pond fertilization or cladoceran controls. A weekly application of dipterex at 0.05 mg/L reduced cladoceran biomass but enhanced rotifer biomass. Our results indicate with a careful management plan it is possible to synchronize the rotifer development with larval fish stocking.     

Natural spawning, early development and first feeding of the semicircle angelfish [Pomacanthus semicirculatus (Cuvier, 1831)] in captivity

Successful natural spawning of Pomacanthus semicirculatus in captivity from 11 September to 18 October, 2006 is described for the first time. Each female laid an average of 230 000 eggs during the spawning period. Fertilized eggs were spherical, transparent and buoyant and had a mean diameter of 0.61 ± 0.03 mm (mean ± SD). Embryonic development lasted 18–21 h at 28.5 °C. Newly hatched larvae were 1.35 ± 0.02 mm in total length (TL) with 27 (12+15) myomeres and had an oil globule in the ventroposterior area of the yolk sac. Larvae completed yolk absorption within 3 days post hatching at 2.37 ± 0.05 mm TL. Larvae were fed either 100% microalgae ( Nannochloropsis sp.), 100% s-type rotifers ( Brachionus rotundiformis ), 100% dinoflagellates ( Gonyaulax sp.) or different combinations of the three (50%:50%:0%, 30%:35%:35%) to determine the effect of live feed on the survival rate. The survival was significantly ( P <0.001) better in larvae fed a combination of diets (30%: 35%: 35%) than others. These results indicate that P. semicirculatus is a potential species for captive-breeding programmes and the use of a combination of diets (microalgae plus s-type rotifers and dinoflagellates) may be a suitable first food for fish larvae.     

Vertical distribution of jack mackerel Trachurus japonicus larvae in the southern part of the East China Sea

ABSTRACT:   The vertical distribution of jack mackerel Trachurus japonicus larvae was described based on discrete depth sampling using a MTD net system from the surface down to 100 m depth at 13 stations in the southern East China Sea between 27 February and 10 March 2002. Of the 20 782 fish larvae collected, T. japonicus larvae were most abundant, accounting for 37.0% of the total catch. The average abundance of the larvae was 419.0 individuals/10 m², with the average (± standard deviation [SD]) body length of 2.6 ± 0.3 mm (range 1.8–7.5 mm). The larvae were concentrated in the mixed layer, with peak densities in the 10–30 m layer. The average (±SD) weighted mean depth was 21.5 ± 7.8 m. There was no evidence of either diel or ontogenetic vertical migration for the early larvae of <5 mm. More than 90% of the T. japonicus larvae were collected in the water temperature ranging from 21 to 23°C. Vertical profiles of the larval densities and chlorophyll a coincided with each other, which might reflect the abundance of their main prey organisms, copepod nauplii and copepodites, since copepod production is known to be closely related with the chlorophyll a concentration.     

Modification of 0+ perch foraging behaviour by indirect cues of predation risk

Abstract –  Intake rate and prey size selection of 0+ perch, Perca fluviatilis , from Lake Wallersee (Austria) was studied at different illumination (day light: 400 lx, twilight: 2 lx) during 5 days of habituation to novel surroundings in aquaria. The hypothesis was tested that high illumination and novelty of surroundings (transfer from holding to test aquaria) as indirect cues of predation risk influences 0+ perch foraging behaviour. Significantly lower total intake and lower proportion of large Daphnia magna (two prey size groups, 2.9 and 1.2 mm, were used) were observed at higher illumination and under novel surroundings. Habituation to novelty caused an increase in consumption of large prey and decrease in consumption of small prey. During the whole period of habituation, more large prey was ingested at twilight than at daylight; no light-induced difference in ingestion of small prey was found. Foraging 0+ perch responded to indirect nonspecific cues of predation risk by reduction of intake of large prey, which are costly in terms of handling time. This allows fish to be more vigilant without ceasing their foraging activity even in potentially dangerous situations. In the lake, young perch are most vulnerable to abundant piscivorous fish and birds during the day; in twilight perch can afford a more time-consuming foraging activity.     

Comparison of pelvic fin rays, scales and otoliths for estimating age and growth of bull trout, Salvelinus confluentus

Abstract  The suitability of three anatomical structures to determine age and growth of bull trout, Salvelinus confluentus (Suckley), was assessed. Scales and pelvic fin rays collected from recaptured bull trout 96–265 mm TL were used to validate annulus formation and assess the accuracy and precision of back calculation. Ageing precision and agreement of assigned ages were compared among scales, fin rays and otoliths from bull trout 52–711 mm TL. Annulus formation was validated for 88% (14 of 16 fish) of recaptured bull trout using pelvic fin rays and 68% using scales (15 of 22 fish). Annulus formation in fin rays occurred between late April to early June, and the hyaline (non-growth) band began forming in late August. Back-calculated length was not significantly different from measured length at initial capture either for fin rays or scales ( P  ≥   0.19), and absolute percent error was 7.2 ± 1.2 (mean ± SE; n  =   14) for fin rays and 8.7 ± 1.9 ( n  =   15) for scales. Consistency of back-calculated lengths at age between tag and recapture samples for individual fish was similar for fin rays (mean absolute difference = 8.2% ± 0.9; n  =   33) and scales (9.4% ± 1.4; n  =   40). However, fin rays (87% precision) and otoliths (90%) provided notably higher ageing precision than scales (68%) and closer agreement of assigned ages, particularly for fish older than age 4. Pelvic fin rays appear to offer more accurate and precise age and growth determinations than scales and a non-lethal alternative to otoliths, but further work is needed to validate the accuracy and precision of ageing large, migratory bull trout.     

Predation on fish larvae by moon jellyfish <Emphasis Type="Italic">Aurelia aurita</Emphasis> under low dissolved oxygen concentrations

ABSTRACT:   Laboratory experiments were conducted to test the hypothesis that low dissolved oxygen concentrations have the potential to enhance the predation rate on fish larvae by moon jellyfish Aurelia aurita which is increasing in abundance in the coastal waters of Japan. Larvae of the red sea bream Pagrus major in four size classes (2.9, 4.1, 6.2 and 8.6 mm in standard length) were used as prey in a short-term predation experiment. No change in the bell contraction rate of the jellyfish (mean bell diameter, 100.4 ± 10.2 mm) was observed at the oxygen concentrations tested (1, 2 and 4 mg/L, and air-saturated, 5.5–6.0 mg/L), suggesting a strong tolerance to a decline in the oxygen concentration. More than 80% of the 2.5 and 4.1-mm size-class larvae were predated on by the jellyfish at all oxygen concentrations during the 15-min trials in 10-L tanks. The 6.2 and 8.6-mm size-class larvae were able to escape from the jellyfish apparently due to their developed swimming ability at the two higher dissolved oxygen concentrations. There was an increase in predation on larvae of these two size classes at the two lower dissolved oxygen concentrations. Predation by moon jellyfish on fish larvae can be more intense at low dissolved oxygen concentrations that commonly occur in the coastal waters of Japan.     

Ontogeny of anti-predator behavior in hatchery-reared jack mackerel Trachurus japonicus larvae and juveniles: patchiness formation, swimming capability, and interaction with jellyfish

ABSTRACT:   Laboratory rearing and behavioral observations of larval and juvenile jack mackerel Trachurus japonicus were conducted to elucidate their life-history traits with emphasis on the interaction with the moon jellyfish Aurelia aurita . Jack mackerel were raised from naturally spawned fertilized eggs and they attained 10.3 ± 0.7 (mean ± standard deviation) mm in body length (BL) by 30 days post hatching (dph) and 26.6 ± 1.8 mm BL at 48 dph raised at 19.3–25.0°C. Patchiness (dense aggregation) was confirmed from 5–16 dph (2.9–5.9 mm BL) during the day and from 9–48 dph (4.0–27 mm BL) at night. Cruise and burst swimming speeds were 1.5–1.9 BL/s and 16–24 BL/s, respectively, during larval and juvenile stages, in experimental tanks. Although escape performance from jellyfish was not different between the larvae of jack mackerel and chub mackerel Scomber japonicus , both species showed better survival compared to red sea bream Pagrus major larvae of a similar size. Although jack mackerel were slow in growth, their slow cruise swimming may reduce the chance of encountering predators and fast burst swimming may help escape from gelatinous predators.     

Size-dependent predation on marine fish larvae by Ctenophores, Scyphomedusae, and Planktivorous fish

Size-dependent predation rates on marine fish larvae by the ctenophore Mnemiopsis leidyi , scyphomedusa Chrysaora quinquecirrha , and planktivorous fish Anchoa mitchilli were estimated via experiments in 3.2 m³ me-socosms. Predation rates on larvae of the goby Gobio-soma bosci were estimated in relation to 1) length of larval prey, 2) presence or absence of alternative < 1 mm zooplankton prey, and 3) a predator-prey interaction between the scyphomedusa and ctenophore. The consumption rate of larvae by the three predators generally declined as larval length increased. The ctenophore ate fewer (1.0 d^-1 per predator) larvae than did the medusa (7.8 d ^-1 per predator) or bay anchovy (4.0 d ^-1 per predator), but it consumed larvae in all size classes tested (3.0–9.5 mm SL). Predation by bay anchovy and the medusa was more size-dependent: 3.0–5.0 mm larvae were most vulnerable. Fewer larvae were eaten by the ctenophore and bay anchovy when zooplankton alternative prey was available, but predation on larvae by the medusa was not influenced by alternative zooplankton prey. Consumption rate of fish larvae by the medusa was reduced 20–25% when the ctenophore was present as its alternative prey. An encounter-rate model was developed and its parameters estimated from the experimental results. Model simulations indicated that the relationship between larval size and vulnerability is dependent on size, swimming speed, and behavior of both predators and larvae, and that bigger or faster-growing fish larvae are not always less vulnerable to predation.     

Effect of different diets on larval production, quality and fatty acid profile of the marine ornamental shrimp Lysmata amboinensis (de Man, 1888), using wild larvae as a standard

The present work evaluates the influence of broodstock diets [Marine Cuisine^®– MC, MC supplemented with highly unsaturated fatty acid- (HUFA) enriched Artemia biomass – MC + AB, and MC supplemented with squid – MC + S] on larval production, newly hatched and early zoeal stage survival and fatty acid profile of newly hatched larvae of Lysmata amboinensis . These parameters are compared with those from larvae hatched from embryos spawned in the wild. The number (±SE) of larvae produced with MC and MC + S (1077 ± 219 and 1103 ± 184, respectively) was similar to that in broodstock carrying embryos spawned in the wild (1224 ± 111), while those fed MC + AB displayed significantly lower values (1044 ± 161). Larvae produced with MC + AB displayed lower survival for all starvation periods, while larvae spawned in the wild displayed the highest survival. No larvae resisted 144 h of starvation and none moulted to zoea II. The fatty acid comparison revealed that larvae from embryos spawned in the wild displayed the highest levels of DHA, as well as higher DHA/EPA and n -3/ n -6 ratios. These results suggest that broodstock diets commonly used to promote ornamental shrimp's maturation (based on mixed frozen components) are far from being optimal.     

Morphological development of eggs, larvae and juveniles of laboratory-reared Ryukyu-ayu Plecoglossus altivelis ryukyuensis

ABSTRACT:   The development of embryos, larvae and juveniles of the Ryukyu-ayu, Plecoglossus altivelisryukyuensis are described based on laboratory-reared specimens.The eggs were spherical, 0.98–1.18 mm (mean 1.06 mm)in diameter with an adherent membrane. The incubation period after fertilizationwas approximately 155 h at a water temperature of 19.7–22.0°C(mean 20.7°C). Newly hatched larvae were 5.0–5.9 mm(mean 5.5 mm) in body length (BL) with 59–62 myotomes.Within 5 days after hatching, the larvae had attained 6.4–8.2 mm(mean 7.8 mm) BL and had completely consumed their yolk.Notochord flexion began at 13.7 mm BL and was completedby 16.3 mm BL. The rudimental dorsal, anal, pelvic andadipose fins appeared at 14.7, 16.3, 21.8 and 21.8 mm BL, respectively.All fin rays reached the same fixed number of adult fish at about28 mm BL. The comb-like teeth began to form at approximately30 mm BL and were fully developed at about 40–50 mm BL.The proportions of P. a. ryukyuensis specimens,which were consistent with adult fish, occurred at approximately40 mm BL.     

Assessment of residency and movement of the endangered bullhead (Cottus gobio) in two Flemish rivers

Abstract –  Residency and movement of bullheads ( Cottus gobio ) were assessed by mark-recapture from November 2001 to June 2002 in two Flemish rivers [Steenputbeek (SPB), Laarse Beek (LB)]. Although the majority of the recaptured bullheads (SPB: 66%; LB: 55%) was found in their initial tagging site before the spawning season, some fish had covered distances between 10–100 m (mean: 17 ± 2 m) and 10–70 m (mean: 18 ± 7 m), respectively. During the spawning season, the proportion of fish that moved (SPB: 58%; LB: 75%) and the distances travelled (SPB: between 10 and 90 m, mean 26 ± 3 m; LB: between 30 and 260 m, mean 133 ± 3 m) were significantly larger. In addition, analysis of individual movement behaviour of multiple recaptured bullheads showed that some fish were either always resident or mobile, while others switched between both behaviours. In general, our results suggest that not all bullheads exhibit sedentary behaviour but that the populations under study consist of both stationary and mobile individuals.     

Diet and Light Intensity Effects on Survival, Growth and Pigmentation of Southern Flounder Paralichthys lethostigma

Interest in the culture of flatfishes has increased globally due to high consumer demand and decreased commercial landings. The Southern flounder Paralichthys lethostigma inhabit South Atlantic and Gulf of Mexico waters and support important commercial and recreational fisheries. In spring, 1996, a two-part larval rearing study was performed with Southern flounder to examine the effects of three larval diets and two light intensities on survival, growth, and pigmentation. The first part of the study consisted of feeding 6 d post-hatch (dph) (3.0 ± 0.1 mm TL) larvae three diets: 1) rotifers Brachionus plicatilis at a rate of 10/mL from day 1–9 and Artemia nauplii (3/mL) from day 7 through metamorphosis; 2) rotifers fed day 1 through metamorphosis and Artemia fed day 7 through metamorphosis; or 3) same diet as treatment 1 plus a commercial larval diet added day 13 through metamorphosis. The second part of the study examined the effects of two light levels: low-light (mean 457 lux) and high-light (mean 1362 lux). At 24 C, metamorphosis began on day 23 (mean fish size 8.2 ± 0.6 mm TL) in all treatments and was completed by day 30. Analysis of survival, size, and pigmentation data indicated there were no significant differences among feed treatments or between light treatments. Overall survival was 33.4% (±15.9) and mean length was 11.5 mm TL ± 1.3. Only 35% of the larvae were normally pigmented. Reexamination of the pigmentation on day 37 indicated fish reared at the low light intensity through metamorphosis (day 30) but exposed to high light intensity for 1 wk post-metamorphosis had become significantly more pigmented.     

Decreasing trophic efficiency in cool-water aquaculture ponds: size-selective predation removes large prey

Maximizing young-of-year (YOY) fish production in an aquaculture setting depends on matching predatory demand with prey availability. With a size-selective YOY fish species (saugeye: Sander vitreus Mitchell females × S. canadense Griffith & Smith males) supplied with natural zooplankton prey ( Bosmina sp. Baird), selective removal of larger individuals may decrease prey fecundity. However, increased nutrient fertilization may also ameliorate the top-down effects of fish predation. We tested these interactions in outdoor earthen production ponds (ca. 4000 m²; n =12) by measuring Bosmina sp. size at first reproduction (SFR), maximum size (MAX) and neonate size (NEO) in ponds that varied in YOY saugeye densities (18–50 saugeye m⁻³) and also differed in phosphorus maintenance levels (either 20 or 30 μg PO₄-P L⁻¹). We found that SFR decreased by 8% [from 0.298 mm±0.007 (mean±1 SE) to 0.275 mm±0.005], MAX decreased by 11% (from 0.367 mm±0.009 to 0.328 mm±0.009) and NEO decreased by 5% (0.198 mm±0.004 to 0.189 mm±0.003) over the range of saugeye densities, and that SFR increased by 4% (from 0.279 mm±0.004 to 0.290 mm±0.003) and MAX increased by 3% (from 0.336 mm±0.004 to 0.347±0.004) with increased fertilization. Further, prey offspring lengths strongly related to mother lengths and lengths differed from early to late in the production season. These results indicate that multiple factors affect prey sizes and emphasize that the removal of large prey individuals by size-selective YOY predators may decrease trophic efficiency, ultimately decreasing fish production.     

Diet shift of larval and juvenile landlocked Ryukyu-ayu <Emphasis Type="Italic">Plecoglossus altivelis ryukyuensis</Emphasis> in the Fukuji Reservoir,Okinawa Island,Japan

ABSTRACT:   The diet shift of larval and juvenile Ryukyu-ayu Plecoglossus altivelis ryukyuensis was investigated for the landlocked population stocked in the Fukuji Reservoir, Okinawa Island. Gut contents of 274 specimens (5.1–31.4 mm in body length) including 31 yolk-sac larvae (5.7–8.0 mm) were examined. The diet of larval and juvenile landlocked P. a. ryukyuensis was mainly composed of zooplankton such as dinoflagellates, rotifers, copepods, and cladocerans. Feeding incidence was 48% in total and it gradually increased with growth. Diet analysis clearly demonstrated a diet shift during the larval and juvenile periods. For yolk-sac larvae and 5.0–19.9 mm fish, the diet was dominated by dinoflagellates Gymnodinium sp., and Peridinium sp., both numerically and by frequency, followed by rotifers that mainly consisted of Polyarthra spp. Diet breadth (Levin's standardized index B_A) diversified with growth, and feeding on copepods and cladocerans gradually increased in 10.0–14.9 mm fish. Diet overlap (Morisita's index: C) showed that diet drastically changed in 20.0–24.9 mm fish with a specialization on cladocerans Bosminopsis deitersi and Diaphanosoma brachyurum . This diet shift probably corresponded with an increase of feeding ability resulting from an enlargement of the mouth, increased swimming ability, and the development of sense organs.     

Production and predation rates in a cannibalistic Arctic char (Salvelinus alpinus L.) population

Abstract – Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11–14.30) kg · ha⁻¹. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50–1.06) kg · ha⁻¹. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74–8.03) kg · ha⁻¹ · year⁻¹, and production (±95% CL) of cannibalistic char to 0.19 (0.15–0.33) kg · ha⁻¹ · year⁻¹. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%.     

Using underwater cameras to describe the reproductive behaviour of the endangered eastern freshwater cod Maccullochella ikei

Abstract –  Underwater cameras were used to observe the breeding behaviour of the endangered eastern freshwater cod, Maccullochella ikei , over 3 years and across three areas in the Mann and Nymboida rivers, Australia. The annual breeding season for M. ikei was short and succinct, lasting only 8–10 weeks. Spawning commenced each year in the lowest altitude area during the first week of spring, and approximately 1 week later in the closest upstream area. Day-length is the primary spawning cue for M. ikei , but increasing water temperature may also be of importance. Nesting sites were located in slow-flowing pools, under cover such as large boulders and bedrock shelves, at depths of 0.9–4.0 m, and with one or two entrances only. The nesting site was vigorously cleaned by the male up to 1 week prior to spawning and was only entered by the female for spawning. Paternal care of eggs and larvae was undertaken for up to 24 days, after which larvae dispersed. Greater protection of breeding M. ikei must be a management priority to ensure long-term conservation of the species.     

Effect of light intensity,prey density,and ontogeny on foraging success and prey selection of larval yellow perch (Perca flavescens)

Light intensity has been shown to influence the foraging success of larval fish. However, the effect of light intensity on larval foraging is likely variable and influenced by both the density and characteristics of planktonic prey. In this study we examined the influence of light intensity of 0.1, 2.0, and 60 μmol·s^?1·m^?2 Photosynthetically Active Radiation (PAR) on foraging of yellow perch (Perca flavescens) larvae at two prey densities. We fed them with a mixture of zooplankton taxa common to lakes inhabited by yellow perch. In addition to light intensity and prey density, the effect of larval yellow perch size was examined by using fish ranging from 9 to 15 mm. The results of our study indicated that yellow perch larvae are well adapted to feed at a wide range of light intensities, as there was no difference in foraging success at investigated light intensities. Increasing prey density from 25 to 150 (zooplankton·l^?1) significantly improved the foraging success of larval yellow perch. However, the influence of prey density on foraging success was dependent on fish length. Improved foraging success at increased prey densities occurred only for individuals with a total length >10 mm. Overall, prey selection by fish larvae was influenced by light intensity, prey density, and fish length. However, the factors that influenced selection for specific prey types differed. Our study, combined with evidence from other field and laboratory work, highlight the need for a better understanding of the influence of prey density on foraging throughout ontogeny.     

Nutritional and density-dependent responses of some cladocera

Abstract. Four cladoceran species of importance as fish food organisms, viz. Daphnia similes (Claus), Simocephalus vetulus (Schodler). Moina macrocopa (Straus) and Ceriodaphnia cornuta (Sars), were raised in the laboratory on nutrient sources including manures, rice bran and Chlorella. The organisms responded better with rice bran and Chlorella.
The productivity of culture organisms appeared to depend upon inoculum and residual densities, indicating a relationship between periodic harvesting and increased production. Associated study reveals the importance of space per individual in the success of laboratory cultures. The optimum space requirement of each species determined by the size of culture organism may vary from 4·5cm³ per individual for small species like Ceriodaphnia to 41·8cm³ per individual for the larger species, Daphnia.     

温瑞塘河后生浮游动物群落结构及其与环境因子的关系

2011年1-7月对温瑞塘河后生浮游动物的群落结构及其栖息环境进行了调查,10个采样点共鉴定出后生浮游动物24种;其中,轮虫15种、枝角类6种、桡足类3种;优势种包括萼花臂尾轮虫(Brachionus calyciflorus)、壶状臂尾轮虫(B.urceus)、镰状臂尾轮虫(B.falcaty)、前节晶囊轮虫(Asplanchna priodonta)、长三肢轮虫(Filinia longiseta)、长足轮虫(Rataria neptunia)、指状许水蚤(Schmackeria inopinus)、广布中剑水蚤(Microcyclops leuckarti)和多刺裸腹溞(Moina macrocopa),优势种组成随季节变化略有不同;浮游动物的月均密度为13.39 ～310.8个/L,月均生物量为0.29 ～ 26.04 mg/L,两值均随水温的升高而增高;就空间分布状况看,浮游动物密度和生物量在各样点间存在明显差异.浮游动物与环境因子的典范对应分析(CCA)结果显示,温瑞塘河的水温是影响浮游动物密度变化最主要的因素(P≤0.05);而高锰酸钾指数( CODMn)、总氮(TN)和氨氮(NH4+)对浮游动物密度的分布也有重要影响,但总氮的变化趋势由NH4+的多少决定.建议在温瑞塘河水环境治理过程中,重点关注水体CODMn和NH4+的分布状况.