Larval Fish Densities Research Articles

Larval fish movement in the River Lohajang,Tangail, Bangladesh

AbstractLarval fish drift and distribution patterns were studied in the River Lohajang, a tributary of the River Jamuna, Bangladesh, during the monsoon seasons (June ‐ October) of 1992, 1993 and 1994. Larval fish drift peaks with the water levels of the River Jamuna. In all three years, the Indian carp, Catla catla, Labeo rohita L. and Cirrhinus mrigala, were associated with the first pulses, but were absent from drift samples after September. Hilsa species and other non‐identified fish species were found throughout the monsoon season. The highest larval fish densities were found in the upper strata of the river, near the shore. The drift densities of these fish became evenly distributed through time. Water turbidity probably influenced the vertical and horizontal distribution, and the absence of diel patterns. The most important species in the larval drift were Hilsa spp., followed by Labeo rohita L., Glossogobius giuris L. and Rasbora daniconius. Among the major carp, Labeo rohita was the dominant species, contributing 80‐90%. The impact of flood control programmes on the reproduction of riverine and larval fish drift is discussed.

Competition between Larval Fishes in Reservoirs: The Role of Relative Timing of Appearance

In small, hypereutrophic reservoirs (<100 ha; >100 μg total phosphorus/L), larval gizzard shad Dorosoma cepedianum and threadfin shad D. petenense (henceforth, shad) reach high densities in the limnetic zone, virtually eliminate zooplankton, and perhaps compromise success of other planktivorous larvae, such as bluegill Lepomis macrochirus. Because relative timing of appearance of shad and bluegills probably influences their relative success, we quantified densities of fish larvae and zooplankton during spring through summer in three reservoirs across 8 years (1987–1994), and we conducted three hatchery experiments with varying larval appearance times and gizzard shad densities in plastic bags (1 m3). When shad were abundant in reservoirs, bluegill abundance often peaked either at the same time (36% of reservoirs and years combined) or after (40% of reservoirs and years combined) shad peaks. When gizzard shad were placed in bags 2 weeks before bluegills (N = 1 experiment), they depleted zooplankton, reducing growth (∼0.075 g·g−1·d−1) but not survival of bluegills. In experiments (N = 2) in which both species were added simultaneously, zooplankton declined only slightly with gizzard shad, and there was little effect on bluegill growth (∼0.21 g·g−1·d−1) and survival; in general, gizzard shad growth declined with time and increasing gizzard shad density. Based on experiments, bluegill success should vary among reservoirs and years as a function of their appearance relative to gizzard shad. In reservoirs, zooplankton availability and bluegill abundances were consistently low during years when gizzard shad dominated reservoir fish assemblages. Because gizzard shad probably reduce bluegill success in hypereutrophic Ohio reservoirs, management strategies that reduce gizzard shad should improve bluegill success.

Dynamics of Ichthyoplankton in the Kanawha River, West Virginia

ABSTRACT Ichthyoplankton distribution and abundance were examined in the upper Kanawha River in the main channel, main-channel border (nearshore), and shoreline habitats. Drift of larval fish was comprised of 25 taxa distributed among 11 families and occurred from early April to late August, with peak densities in early June. Fish larvae appeared and densities peaked at water temperatures of 8.5°C and 22°C, respectively. Larval freshwater drum (Aplodinotus grunniens) was the most abundant taxa followed by Clupeidae, common carp (Cyprinus carpio), and other Cyprinidae. Clupeidae, common carp, and freshwater drum dominated main channel and nearshore collections. Cyprinidae, Catostomidae, and bluegill sunfish (Lepomis macrochirus) dominated shoreline collections. Most fish larvae (99%) collected in the main channel and nearshore habitats were protolarvae, while the larger larvae, meso- and metalarvae, were more abundant along the shoreline. In the main channel, fish larvae and eggs were generally distributed throughout the water column, but at times were more abundant on the bottom. Generally, larval fish densities were lower in the main channel compared to nearshore habitats.

Establishment of a Fish Community in the Hayden-Rhodes and Salt-Gila Aqueducts, Arizona

Fish populations were studied in the Central Arizona Projectˈs canal system during the first 4 years of aqueduct operation (1986–1989). Ichthyoplankton entering the canal from Lake Havasu averaged 1 larva/m3 during April–June 1987 and 1988. Larval fish densities increased significantly in downstream samples, substantiating diver observations that fish were spawning in the canal system. Of the 16 fish species collected, 14 were assumed to have originated from Lake Havasu and 2 were introduced by anglers from their bait buckets. Initially, the fish community was dominated numerically by threadfin shad Dorosoma petenense (>88%), centrarchids (< 10%), cyprinids (<2%), and striped bass Morone saxatilis (<I%). However, as annual water diversions increased from 1.3 × 108 m3 in 1986 to 9.4 × 108 m3 in 1989, community composition shifted from clupeids to centrarchids (70%). Fish densities dropped from an estimated 1,260 fish/ha in 1986 to 17 fish/ha in 1989, and biomass dropped from 116 to 73 kg/ha. Declines were attributed to higher operational velocities, associated scour, deprivation, and predation. Although initial populations adjusted downward to planned operational conditions, the fish community continued to represent a potentially valuable, but as yet unused, resource.

Development of an intensive culture system for sea bass ( Dicentrarchus labrax) larvae in sea enclosures

A system for the intensive production of sea bass larvae ( Dicentrarchus labrax) in sea structures was developed between 1987 and 1994. In 1994, this system was used successfully for two larval rearing cycles (with 400000 and 420000 2-day-old larvae) at a fish farm. One hundred days after hatching the survival rate was 11%, and the mean weight of fish was 2.5 g. The water temperature varied from 13.9 to 25.4 °C in the cylindro-conical enclosures (40 m 3) which were set in the sea. The density of fish larvae at starting time was about 10 1 −1. Larvae were fed initially with Artemia nauplii (hatched out on land). Digestive content observations showed that they also fed on natural plankton in the enclosure. Weaning onto microparticles started when the mean length of the larvae reached 12 mm. Temperature variations were largely dependent on the water surrounding the enclosure but the chemical parameters inside were quite different from those of the sea. Many problems solved during the preliminary experiments are discussed, including the control of fouling, but contamination by predators or competitors is still a risk. The natural food web which develops in the enclosure, with the fish larvae as the main predators, seems to be an advantage for larval rearing. The use of such an enclosure system, which is not expensive and is easy to set up at a farm, is discussed.

Effect of larval fish and nutrient enrichment on plankton dynamics in experimental ponds

The hypotheses that larval fish density may potentially affect phytoplankton abundance through regulating zooplankton community structure, and that fish effect may also depend on nutrient levels were tested experimentally in ponds with three densities of larval walleye, Stizostedion vitreum (0, 25, and 50 fish m−3), and two fertilizer types (inorganic vs organic fertilizer). A significant negative relationship between larval fish density and large zooplankton abundance was observed despite fertilizer types. Larval walleye significantly reduced the abundances of Daphnia, Bosmina, and Diaptomus but enhanced the abundance of various rotifer species (Brachionus, Polyarthra, and Keratella). When fish predation was excluded, Daphnia became dominant, but Daphnia grazing did not significantly suppress blue-green algae. Clearly, larval fish can be an important regulator for zooplankton community. Algal composition and abundance were affected more by fertilizer type than by fish density. Inorganic fertilizer with a high N:P ratio (20:1) enhanced blue-green algal blooms, while organic fertilizer with a lower N:P ratio (10:1) suppressed the abundance of blue-green algae. This result may be attributed to the high density of blue-green algae at the beginning of the experiment and the fertilizer type. Our data suggest that continuous release of nutrients from suspended organic fertilizer at a low rate may discourage the development of blue-green algae. Nutrient inputs at a low N:P ratio do not necessarily result in the dominance of blue-green algae.

Ichthyoplankton Abundance along a Recruitment Corridor from Offshore Spawning to Estuarine Nursery Ground

Two temporally separate larval fish assemblages were identified from ichthyoplankton samples collected between November 1987 and January 1990 along a transect from offshore to Oyster Bayou tidal pass into Fourleague Bay, Louisiana. The warm water species (e.g. bay anchovy, naked goby, Microgobius sp., spotted seatrout and skilletfish) dominated in water temperatures >23 °C and the cooler water species (e.g. gulf menhaden and Atlantic croaker) dominated in water temperatures <23 °C. These assemblages were characterized by different life-history strategies, distributions, and seasonal abundances suggesting that they utilize resources in different locations and times. Analysis of Oyster Bayou tidal pass data indicated that larvae from all species were more abundant on flood than ebb tides and larval fish densities were often statistically greater near bottom, suggesting tidal transport and/or retention. In addition, larger larval bay anchovy and gulf menhaden were taken in the middle of the tidal pass during flood tides. During ebb tides, however, larger bay anchovy larvae were taken along the pass edges, suggesting behaviourally mediated transport into and/or retention within the estuary.

Growth and Survival of Larval Fishes: Roles of Competition and Zooplankton Abundance

-Interactions among larval gizzard shad Dorosoma cepedianum, bluegills Lepomis macrochirus, and their zooplankton prey were examined in a controlled mesocosm experiment and by field sampling. In the mesocosm experiment, gizzard shad growth and survival were negatively correlated with gizzard shad density and positively correlated with macrozooplankton prey. Bluegill growth was positively correlated with prey availability, but survival was uniformly high despite differences in zooplankton abundance and fish density. Macrozooplankton and copepod biomasses were negatively correlated with fish density. In Lake Shelbyville, co-occurrence of larval gizzard shad and bluegills in the limnetic zone was limited to a 3-week period, and the period of greatest larval gizzard shad abundance preceded the appearance of bluegills. Zooplankton abundance declined greatly after the peak in larval gizzard shad abundance and remained low when bluegills were present. Growth rates of gizzard shad were highest early and declined throughout the summer, whereas bluegill growth was highest during mid to late summer. Growth rates of gizzard shad and bluegills in the field were not correlated with fish density. However, as in the mesocosm experiment, zooplankton biomass was negatively correlated with fish density, bluegill growth was correlated with the abundance of zooplankton prey, and bluegill survival was uniform through time and not related to fish density or zooplankton abundance. Diet overlap was substantial; gizzard shad and bluegills fed selectively on smaller prey items in June, switching to larger cladocerans and copepods by July. Our results suggest that growth and survival of planktivorous larval gizzard shad and growth of larval bluegills are affected by availability of zooplankton prey, which may become limiting when larval fish densities are high.

Ichthyoplankton abundance along a recruitment corridor from offshore spawning to estuarine nursery ground

Two temporally separate larval fish assemblages were identified from ichthyoplankton samples collected between November 1987 and January 1990 along a transect from offshore to Oyster Bayou tidal pass into Fourleague Bay, Louisiana. The warm water species (e.g. bay anchovy, naked goby, Microgobius sp., spotted seatrout and skilletfish) dominated in water temperatures >23 °C and the cooler water species (e.g. gulf menhaden and Atlantic croaker) dominated in water temperatures <23 °C. These assemblages were characterized by different life-history strategies, distributions, and seasonal abundances suggesting that they utilize resources in different locations and times. Analysis of Oyster Bayou tidal pass data indicated that larvae from all species were more abundant on flood than ebb tides and larval fish densities were often statistically greater near bottom, suggesting tidal transport and/or retention. In addition, larger larval bay anchovy and gulf menhaden were taken in the middle of the tidal pass during flood tides. During ebb tides, however, larger bay anchovy larvae were taken along the pass edges, suggesting behaviourally mediated transport into and/or retention within the estuary.

Microhabitat use by marsh-edge fishes in a Louisiana estuary

We used a drop sampler to characterize use of the marsh-edge ecotone by small fishes along two transects running inland from the Gulf of Mexico for ca. 25 km in Louisiana's Barataria-Caminada Bay System. Monthly sampling was stratified among upper, middle, and lower reaches and within reaches to characterize fish responses to salinity, depth, distance from shore, substrate, dissolved oxygen concentration, temperature, turbidity, velocity, and emergent stem density. In 681 quantitative samples, covering 658 m2, collected between October 1987 and October 1989, we collected 57 fish species and 16 864 individuals, primarily larvae and juveniles. The 15 most abundant fishes, comprising 97.7% of all individuals, were concentrated near the marsh edge (i.e., 0 to 1.25 m distance). Some significant differences within species for seasonal variables (e.g., temperature and dissolved oxygen concentration) reflected the ephemeral duration of early life history stages. Other differences reflected ontogenetic microhabitat shifts (e.g., depth and distance from shore). Within ecological groups, characterized as demersal residents, nektonic transients, and demersal transients, spatial and temporal segregation reflected the particular habitat requirements of each species. In a principal component analysis of microhabitat use, the first three components were interpreted as seasonal, depth-and-distance, and salinity axes, respectively. The array of species and size classes in principal component space reflected the complex dimensionality of microhabitat use. The high density of fish larvae and juveniles near the marsh edge confirmed the importance of the marsh-edge ecotone as a nursery for many estuarine-dependent fishes.

The surface accumulation of larval fishes by hydrodynamic convergence within the Mississippi River plume front

In September 1987 and May 1988 densities of larval fishes at the surface were greater within the frontal zone of the Mississippi River plume than they were in plume or shelf waters. Sharp turbidity discontinuities of 10–50 m width accompanied by temperature and salinity discontinuities were embedded within this large-scale frontal zone, which itself spanned 2–20 km. Apparent convergent motion normal to turbidity discontinuities had velocities in the range of 0-0.8 m s −1: lateral shear was also evident. Exceptionally high densities of larval fishes were not always observed at turbidity discontinuities. Turbidity discontinuities, often sinuous in configuration, formed and dissipated over time scales of 2–6 h. Expected densities of larval fishes within frontal convergence zones, calculated with a simplified advection-diffusion model, approximated mean and median densities observed within the large-scale frontal zone.

Composition, distribution and abundance of neustonic ichthyoplankton off northeastern New Zealand

Patterns in the distribution and abundance of ichthyoplankton off the northeastern coast of New Zealand were investigated. Neuston samples were collected monthly between November 1986–November 1987 at stations located 0·5, 3·2 and 6·0 km offshore from each of three locations that were separated by 3–5 km. Three abundant taxa, tripterygiids ( Forsterygion spp.), an engraulid ( Engraulis australis ) and a clupeoid ( Sardinops neopilchardus ) accounted for 80% of the total catch. Ichthyoplankton was at least three times more abundant during the winter month of July than in any other month, primarily due to the large numbers of tripterygiids. Low densities of fish larvae were found during the spring and summer, but many taxa had peaks in abundance at this time. Patterns of along-shore distribution were inconsistent; they varied between months for most taxa. In general, more fish larvae were caught at the sampling stations that were 3·2 or 6·0 km from the shore.

Is dispersal of fish eggs, embryos and larvae an insurance against density dependence?

Dispersal of eggs, embryos and larvae appears to be an effective mechanism for maintaining the densities of fish larvae at sea below levels at which competition for food becomes a critical survival factor. A hypothesis that competition is the selective agent for the evolution of dispersal, also involving unfavourable transportation as a trade-off of dispersal, is proposed. The validity of this hypothesis is investigated by seeking for adaptive connections between the dispersal or retention tendencies and the ecological or biological properties of the species.

Interdisciplinary study on the thermohaline front at the mouth of Tokyo Bay in winter

An intensive field observation was carried out around the thermohaline front at the mouth of Tokyo Bay in order to reveal the physical, chemical and biological characteristics of a thermohaline front. The low water temperature, low salinity, nutrient-rich and high chlorophyll a coastal water and the high water temperature, high salinity, nutrient-poor and low chlorophyll a offshore water converge at the thermohaline front in the surface layer, mix there and sink downward. Some mixed water intrudes into the intermediate layer of offshore water and the other flows into the bottom layer of coastal water like a shirt. The density of fish larvae is higher in coastal water than in offshore water and the highest at the front. On the other hand, the density of copepods is higher in offshore water than in coastal water. The concentration of dissolved oxygen is low near the front due to the respiration of large biomass which are accumulated in the surface layer of the front.

Physicochemical factors affecting larval fish densities in mississippi river floodplain ponds, Louisiana (U.S.A.)

We collected water-quality data from 15 artificial floodplain ponds along the Mississippi River during May 1988 and quantified shoreline length, shoreline sinuousity, volume, and depth variation. Ponds regarded as high-quality nurseries (based upon larval fish densities) contained higher dissolved oxygen concentrations and lower total organic carbon concentrations than ponds of lower nursery quality (p < 0.02). High-quality nurseries also maintained higher conductivity and turbidity than low-quality nurseries (p < 0.05). Results indicated that dissolved oxygen and pH probably fluctuated less in high quality nurseries and therefore provided better conditions for survival and growth of larval fishes. Total organic carbon and conductivity were directly related to pond morphometry (p < 0.004) and affected dissolved oxygen and pH in ponds. Large, high-volume ponds with sinuous shorelines and variable depths tended to contain both high conductivities and low total organic carbon concentrations. Pond morphometry may have affected water quality and subsequently determined the nursery value of artificial floodplain ponds.

Northern Large-River Benthic and Larval Fish Drift: St. Marys River, USA/Canada

Seasonal (summer, winter), diel (day, night), water column (surface, mid-depth, bottom), proximity to shore, weather (calm, windy), and among-transect differences in benthic and larval fish drift were measured during 1985 using 355 μm-mesh nets at three transects in the St. Marys River, the connecting channel between Lake Superior and Lake Huron. Overall, there were 65 benthic ( x ¯ density = 562/1,000 m 3) and 5 larval fish ( x ¯ density = 383/1,000 m 3) taxa collected. Occurrence of significantly higher densities of larval rainbow smelt at the middle transect, Lake Nicolet, indicates that areas above are important spawning sites for this species. Because densities declined at the downstream-most transect, Point aux Frenes, we concluded that rainbow smelt must be utilizing the Lake Munuscong area as a nursery area. Larval fish densities in summer were greater in the channel than nearshore, were greater at night than during the day, and higher in the upper half of the water column than near bottom. Densities of benthos and larval fish were greater in summer than winter. Chironomidae (52–82% of total) was the winter dominant, while Hydra (60%) dominated summer drift. Drift was greater at night than during the day for benthos and fish at two of the three transects, with benthic abundances greater at the bottom than at other depth strata. In summer, benthic drift was highest at shoreline stations and lowest in the channel; in winter there were minimal onshore/offshore differences. Current appeared to be the major factor causing elevated benthic drift rates in winter, while in summer, high winds with concomitant high waves and currents were the main factors producing significantly higher drift densities. High wind conditions produced a reversal of the usually observed diel trend of higher night benthic drift rates at one of the transects, and underscores the importance of wind in modulating drift rates in large river systems such as the St. Marys River. Overall, the multiple regression factors utilized were much more predictive of the drift of benthos than of larval fish.

Effect of Egg and Larval Survival on Year-Class Strength of Lake Whitefish in Grand Traverse Bay, Lake Michigan

A study was conducted in Grand Traverse Bay, Lake Michigan, during 1983 and 1984 to identify factors that are important in determining year-class strength of lake whitefish Coregonus clupeaformis. The major determinants of year-class success were overwintering egg survival and the amount of food available to larval lake whitefish during the first 7 weeks of life, Egg mortality was related to the timing of ice cover, with an early cold winter producing the highest survival. Larval survival was affected by the abundance of available prey, i.e., copepod zooplankton between the sizes of 0.7 and 1A mm in total length. In 1983, when zooplankton of this size were abundant relative to larval fish density, high rates of growth and survival of lake whitefish ensued. In 1984, the prey-per-fish ratio declined greatly, and poor growth and low survival were observed. The dynamics of these early life stages appear to significantly influence both lake whitefish year-class strength and eventual recruitment in Grand Traverse Bay.

Larval fishes and zooplankton in a cyclonic eddy in Hawaiian waters

A cold-core eddy occurred off the Kona coast of the island of Hawaii in July 1982. It remained in that area for ~70 days, sufficient time for many reef fish species to complete their planktonic larval phase. The deployment of eight current drogues in the eddy showed how entrainment of plankton from the reef and adjacent offshore waters can occur and that passive drift can return drifters from the deep sea to shore. Larval fishes may be swept past the island every 7-8 days in a weak eddy and 3.5-5 days in a strong eddy. Plankton collections were made at night near the surface and at the same depth as the current drogues. Zooplankton were most concentrated at the eddy center. Taxonomic analysis of the plankton showed that the dominant animals were calanoid copepods, malacostracans, hyperiid amphipods, gastropod and bivalve larvae and chaetognaths. The densities of zooplankton and larval fishes in the eddy were higher than in the same area before the arrival of an eddy. Larval fishes were most abundant in the periphery and among these, midwater Gsh larvae (gonostomatids and myctophids) were the most numerous. Other numerous Gsh larvae in the eddy included scombrids, particularly Thunnus albacares, carangids and the reef fish, Abudefduf abdommalis (Pomacentridae).

Predation on Larval Fish by Atlantic Mackerel Scomber scombrus, with a Comparison of Predation by Zooplankton

This study reports on the feeding selectivity of Atlantic mackerel, Scomber scombrus, on larval fish (3-10 mm in length) presented as part of natural zooplankton assemblages. As with other vertebrate planktivores, prey preference was positively size selective, contrary to the pattern observed for several invertebrate carnivores. Larval fish density did not significantly influence predation rates. Furthermore, there was no evidence of either switching or saturation of the predator's functional feeding response with changes in alternative prey abundance, again unlike invertebrate predators. A review of previous experiments revealed that capture success of larval fish by predators is a function of the size of larval fish relative to the size of the predator, independent of predator taxa (i.e. vertebrate versus invertebrate).

Spatial Distribution of Entrained Fish Larvae in a Power Plant Discharge Canal

Larval fish were sampled with plankton nets during June and July at 1-, 3-, and 5-m depths at three stations in the 6-m-deep discharge canal of the Monroe electricity-generating plant on western Lake Erie. Of nine species, gizzard shad (Dorosoma cepedianum) accounted for 96% of all larval fish collected in June and, along with freshwater drum (Aplodinotus grunniens), 78% of those taken in July. Densities of fish larvae at the three depths, and at two of the three stations sampled, were not significantly different. Mean densities of gizzard shad and total fish larvae in June were significantly higher at one station. Fluctuating and significantly lower velocity at that station, causing the flowmeter not to turn while the net was still filtering water, was suspected of causing inflated densities. Generally sizes of larvae were not stratified by depth or station; differences that were found were small. Thus, we concluded that to obtain samples with representative species, densities, and sizes of entrained fish larvae, a stationary net should be positioned where the water has uniform high velocity and is well mixed.