Habitat selection by larvae of a fluvial lamprey, <Emphasis Type="Italic">Lethenteron reissneri</Emphasis>, in a small stream and an experimental aquarium

Habitat selection by fluvial lamprey larvae, Lethenteron reissneri (Petromyzontidae), was studied in a natural stream and an experimental aquarium to clarify microhabitat requirements for future conservation of natural populations. A gross collection survey of lamprey larvae in the Monbetsu River, southeastern Hokkaido, Japan, revealed a remarkable bias toward distribution in sandy-mud beds. An analysis using Jacobs' electivity index showed that the larvae selectively utilized spaces having regard to shallow water, weak current, deep sandy-mud, and fine substrate particles. A comparison of microhabitat use between small- (≤5 cm) and large-sized larvae (>5 cm) indicated that the latter utilized the space with greater ranges in both water depth and substrate particle size than the former. Both the field survey and laboratory experiments on larval selectivity of physical habitat variables clearly demonstrated that substrate particle size was the most important variable for small-sized larvae whereas both water depth and substrate depth were more important for large larvae. These findings should be applicable in directing attempts at fluvial habitat restoration for conservation of this endangered lamprey species. Received: November 1, 2000 / Revised: September 12, 2001 / Accepted: October 18, 2001     

The concentration of cadmium,lead, copper and zinc inChironomus gr.thummi larvae (Diptera,Chironomidae) with deformedversus normal menta

The concentrations of Cd, Pb, Cu and Zn inChironomus gr.thummi were determined for 4th instar larvae from the polluted Dyle River, tributary of the Scheldt River (Belgium). Comparison was made between larvae with deformed and normal menta. Deformed larvae showed higher overall metal concentrations than normal larvae. Especially Pb and Cu had higher concentrations in deformed larvae (16.22 mg kg^–1 dry weight and 39.66 respectively) than in normal larvae (12.80 mg kg^–1 dry weight and 35.70 respectively). No significant differences were found in the concentrations of Cd and Zn (mean [Cd] = 0.81 mg kg^–1 dry weight and mean [Zn] = 313.12 mg kg^–1 dry weight). There was no difference between the two larval groups as far as total length, dry weight and developmental stage of the imaginal discs are concerned.     

Analysis of sibling cannibalism among pike,Esox lucius,juveniles reared under semi-natural conditions

Synopsis Sibling cannibalism in pike, Esox lucius, larvae and juveniles living in outdoor rearing ponds was studied using stomach contents analysis. For the two initial densities tested (6 and 18 larvae m^–2, equivalent to 12 and 36 larvae m^–3), cannibalism was non-existent during the larval period (13 to 35 mm total length) and was observed only during the juvenile stages. Initial density of larvae influenced both the date of first detection of cannibalistic individuals and the rate of development of cannibalism in the population. At initial stocking densities of 18 larvae m^–2 (36 larvae m^–3), cannibalism was observed from 21 days after the start of exogenous feeding (mean total length: 60 mm) onwards. At a mean total length of 100 mm and for initial stocking densities of 6 and 18 larvae m^–2, (12 and 36 larvae m^–3), the average proportions of cannibals in the populations of juveniles were 7.8% and 41.3% and the cannibals accounted for 15.5% and 65.9% of the total pike biomass, respectively. In stomachs of cannibals, young pike were the dominant prey in terms of weight. Dry weights of invertebrate-prey were lower in cannibals than in non-cannibals of similar size. Cannibalism among pike juveniles was characterized by the prey being swallowed whole and head first in the vast majority of cases. There was a strong positive correlation between predator and prey size and the mouth size of a cannibal was found to be an important constraint determining maximum victim size. The overall mean ratio of pike prey length to pike cannibal length was 66.2% and the average ratio of prey head depth to predator mouth width amounted to 87.6%. Prey size selection could be demonstrated for several length-groups of cannibals. These results are compared with the characteristics of early cannibalism in other fish species.     

Biometry and trophodynamics of Salpa thompsoni foxton (Tunicata: Thaliacea) near the Antarctic Peninsula in austral summer, 1983–1984

Summary Salpa thompsoni aggregates have a biometric profile similar to that of mid-latitude salps, being approximately 96% water and only about 1% organic matter. Of its ash-free dry weight about 13.6% is carbon and 3.1% is nitrogen. All weight parameters were related to body length by a power function of 2.3. S. thompsoni was a dominant member of the zooplankton community in waters near the Antarctic Peninsula in the austral summer of 1983–1984, with biomass in mid-March ranging from 49 to 671 mgCm^–2 and 9.6 to 146 mgNm^–2. Three subpopulations occurred in separate regions: (1) the Bransfield Strait, (2) north of the South Shetland Islands, and (3) west of Elephant Island; these were dominated by 20, 30 and 40 mm individuals, respectively. Biomass was greatest in the Bransfield Strait and least near the South Shetland Islands. Clearance rate measurements of S. thompsoni on naturally occurring particulate matter were significantly lower than those previously reported for mid-latitude salps, a result which we attribute primarily to the effect of low habitat temperature (ca. 1°C). Direct measurements suggest that fecal production by 21 mm blastozoids is equivalent to 10.2% body carbon d^–1 and 6.6% body nitrogen d^–1. Grazing by S. thompsoni may have removed a majority of the daily primary production in March, but <1% in January. The comparatively low biomass of krill larvae in 1983–1984 may be attributed partially to competitive removal of food by salps, but an equally important effect may have been direct predation.     

Age and growth of Pacific herring larvae based on length-frequency analysis and otolith ring number

Synopsis Age and growth in length and dry weight of cohorts of wild Pacific herring larvae, Clupea harengus pallasi, were measured using successive modes in the length-frequencies of the catches and the number of rings in the otoliths. Average linear rates of growth in length ranged from 0.36–0.41 mm d^–1, and average exponential rates of growth in dry weight ranged from 0.063–0.084 d^–1. Length-date and dry weight-age curves were best described using one-cycle and two-cycle Gompertz functions, respectively. Weight-length relationship were, therefore, curvilinear on double logarithmic plots and were best described by a non-linear allometric function. Average rates of otolith ring deposition were 0.90, 1.09 and 0.73–1.26d^–1. Rings were deposited daily from the day of complete yolk absorption in the first two cohorts, but interrupted ring deposition was observed over the first 27 d of the third cohort. Relatively low water temperatures, <9° C, coincided with the interruption and may have caused it.     

Spawning ecology of the American brook lamprey, <Emphasis Type="Italic">Lampetra appendix</Emphasis>

Synopsis We observed spawning American brook lamprey, Lampetra appendix, in coldwater streams in Minnesota to assess various aspects of their spawning behavior and spawning habitat requirements. Spawning occurred during April and May, at water temperatures ranging from 8.7 to 15.5°C. Average adult lamprey length and mass differed significantly among streams, but there were no significant differences in length or mass between males and females. Overall sex ratio was 1:1, although one stream had significantly more males than females and one stream held significantly more females. Lampreys spawned in groups of 2–14 individuals, averaging 4.2 adults per nest across all streams. Nests were constructed in gravel and cobble substrate just upstream of riffles, spaced at an average density of three nests m⁻². The typical nest was 16 cm in diameter in water 31 cm deep with a bottom current velocity of 14 cm s⁻¹, and was excavated to a depth of 4 cm below the stream bottom; however, some nest characteristics varied significantly in a few streams. Nests were larger in streams with larger spawning groups, deeper water, and slower current velocities. American brook lamprey exhibited spawning behaviors and spawning habitat requirements similar to those of other species of lamprey in North America.     

Ecology and life history of the clown goby inhabiting the upper Banana River,Cape Canaveral,Florida

Synopsis Monthly collections of clown goby,Microgobius gulosus, were made from March 1984 through February 1985 at two stations located at the head of the Banana River, Brevard County, Florida, as part of the long-term environmental monitoring program at the John F. Kennedy Space Center. A total of 18921 fishes comprising eight families and 12 genera was collected.M. gulosus represented 6.4% of the total catch. Populations ofM. gulosus exhibited aggregation behavior, which varied in intensity depending on densities of individuals m^–2 and habitat characteristics. Capture data were best described by the negative binomial distribution. Mean estimates of individuals m^–2 ranged from 0.0 to a high of 22.1 during periods of peak recruitment. The total length-weight regression for all individuals measured was log₁₀ weight = –4.65 + 2.72 log₁₀ length.M. gulosus obtained a size of 35–40 mm TL the first year and 50–60 mm TL the second year. Total lengths of all specimens ranged from 11 to 71 mm. Young of the year first appeared in May with smallest individuals collected in June and July. A protracted spawning period was observed. Stomach and gut analyses revealed that crustaceans and annelids combined represented 65% and 66% of the total diet forM. gulosus from stations 1 (open) and 2 (impounded), respectively. However, differences in proportions of the two groups were present between the two stations. Crustaceans represented 47.1% of the diet for gobies collected at station 1 and annelids 40.8% for specimens collected from station 2. Fecundity was low with the mean number of ova being 305 ± 77.5 for females between 35 and 49 mm TL. Estimated mortality rate was approximately 95% annually.     

Selection and preference of benthic habitat by small and large ammocoetes of the least brook lamprey (<Emphasis Type="Italic">Lampetra aepyptera</Emphasis>)

In this laboratory study, we quantified substrate selection by small (<50 mm) and large (100–150 mm) ammocoetes of the least brook lamprey (Lampetra aepyptera). In aquaria, ammocoetes were given a choice to burrow into six equally-available substrate types: small gravel (2.360–4.750 mm), coarse sand (0.500–1.400 mm), fine sand (0.125–0.500 mm), organic substrate (approximately 70% decomposing leaves/stems and organic sediment particles, and 30% silt and fine sand), an even mixture of silt, clay, and fine sand, and silt/clay (<0.063 mm). Fine sand was selected with a significantly higher probability than any other substrate. Fine sand habitat is limited in many streams, in part owing to geology, but also as a result of channelization and excessive silt/clay sedimentation, which is a conservation concern. Our results indicate that ammocoetes of least brook lampreys are habitat specialists that prefer fine sand habitat. Hence, availability of fine sand habitat may limit distributions and population sizes.     

Growth,fecundity, and egg size of least brook lamprey,Lampetra aepyptera

Synopsis Eight geographically-diverse (33°11N to 39°14N) populations of least brook lamprey varied significantly in density of larvae and mean length of metamorphosing and adult lampreys (101–152 mm). Absolute fecundity (503–5900 eggs) did not change significantly with stage of post-larval development, suggesting little post-metamorphic atresia; egg dry weight increased to stage 6, the penultimate stage of metamorphosis. Absolute fecundity increased with the cubic power of total length. Relative fecundity (250–1124 eggs per gram total body weight) decreased significantly with increasing length within two streams. Relative fecundity, adjusted to a common length, increased with mean length of the population. Conversely, mean egg dry weight (0.09–0.24 mg, stages 6–8) increased with maternal length within three streams, and decreased with length among streams. In populations where spawning occurs at a small body size, females produce comparatively fewer but larger eggs. Large eggs may be required to counter the effects of an unproductive environment and the accompanying reduction in relative fecundity is compensatory. No relationship was evident between latitude, annual thermal units, or density and relative fecundity or egg size. Mean length of a population was also unrelated to these environmental factors.     

Biometrical relationships, energy content and biochemical composition of Neomysis mercedis from Lake Washington

Morphometric relationships, caloric content and biochemical composition of Neomysis mercedis were determined for freshly caught mysids. Strong positive correlations between telson length, carapace length, dry weight, energy content and total length are described by the equations: Ln (Dry weight) = –5.02 + 2.57^* Ln (Total Length), Telson Length = 0.13^* Total Length, and Energy (Calories) = –37.13 + 4.85^* Mean Total Length. Energy (4.92 cal mg^–1 AFDFW), ash (8.61% dry weight) and total Kjeldahl nitrogen (10.6% dry weight) content are comparable to values reported for other species. A comparison of the length-weight relationship for N. mercedis with similar equations published previously for other mysid species indicated that the predicted mean dry weight at any particular length varied among species.     

Experimental estimation of the food intake of larval vendace (Coregonus albula L.) under field conditions

We estimated the food intake of larval vendace (Coregonus albula L.) directly in an experimental chamber under field conditions. The larvae were stocked into net enclosures and reared without additional feeding for 6 weeks immediately after the ice melted in Lake Ylä-Enonvesi, Eastern Finland. The food intake was estimated on the basis of the decrease in zooplankters due to larval predation in the transparent plastic chambers anchored in the littoral zone. The experiments were carried out twice in 1988 and three times in 1989 (May–June). The numbers of zooplankters inside the chambers were counted from the subsamples using an inverted microscope. The relative daily ingestion rate (mg dry mass of prey animals mg dry mass of fish ^–1 24 h^–1) of the larvae of different sizes was: 1.09 and 0.84 for 9–11 mm larvae, 1.27 for 11–13 mm larvae and 0.34 for 17–20 mm larvae. The measured ingestion rate is presumed to be near the maximum consumption of the larvae. This method could provide accurate estimates of food consumption in the field or in the laboratory.     

Small-scale patterns in distribution and feeding of Atlantic mackerel (Scomber scombrus L.) larvae in the Celtic Sea with special regard to intra-cohort cannibalism

Short-term variability in vertical distribution and feeding of Atlantic mackerel (Scomber scombrus L.) larvae was investigated while tracking a larval patch over a 48-h period. The patch was repeatedly sampled and a total of 12,462 mackerel larvae were caught within the upper 100 m of the water column. Physical parameters were monitored at the same time. Larval length distribution showed a mode in the 3.0 mm standard length (SL) class (mean abundance of 3.0 mm larvae =75.34 per 100 m³, s=34.37). Highest densities occurred at 20–40 m depth. Larvae <5.0 mm SL were highly aggregated above the thermocline, while larvae ≥5.0 mm SL were more dispersed and tended to migrate below the thermocline. Gut contents of 1,177 mackerel larvae (2.9–9.7 mm SL) were analyzed. Feeding incidence, mean number (numerical intensity) and mean dry weight (weight-based intensity) of prey items per larval gut were significantly dependent on larval size. However, while weight-based feeding intensities continued to increase with larval length, numerical intensity peaked at 4–4.9 mm SL, indicating a shift in the larval diet. While first-feeding larvae relied most heavily on copepod nauplii and eggs, larvae ≥5.0 mm SL initiated piscivorous feeding. All identifiable fish larvae were Atlantic mackerel. Thus, the piscivory was cannibalism. Larval feeding incidence and numerical feeding intensities peaked during daytime and were reduced at night. Daily ration estimates for first-feeding mackerel larvae <4.0 mm SL were extremely low = 1.43% body dry weight, but increased dramatically at 5.0 mm SL, i.e., at the onset of cannibalism, reaching >50% body dry weight in larva ≥8.0 mm SL. Received in revised form: 31 October 2000 Electronic Publication     

The food and growth of pelagic 0+ Alestes nurse (Characidae) from the Blue Nile,near Khartoum

The food, feeding habits and growth of 0+ Alestes nurse (Rüppel) from the Blue Nile near Khartoum, was investigated. 0+ A. nurse were observed to change their food from phytoplankton and small zooplankton during their pre-metamorphosis stages, to larger zooplankton (Daphnia spp., Chydorus sp.) and insects (larvae, pupae and imagines) during their post-metamorphosis stage.Their growth in length and weight was characterized by two distinct stanzas; during the first stanza, the fish increased in total length at a rate of 0.196 mm mm^–1 wk^–1, and in wet weight at a rate of 0.430 g g^–1 wk^–1. These rates were reduced during the second stanza to 0.046 mm mm^–1 and 0.080 g g^–1 wk^–1, respectively. The calculated value of the exponent b in their length-weight relationship suggested that their growth was allometric.     

Evaluation of entomopathogenic nematodes against the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae)

Infectivity of six entomopathogenic nematode (EPNs) species against Bactrocera oleae was compared. Similar infection levels were observed when third-instar larvae were exposed to infective juveniles (IJs) on a sand-potting soil substrate. When IJs were sprayed over naturally infested fallen olives, many larvae died within treated olives as well as in the soil; Steinernema feltiae caused the highest overall mortality of 67.9%. In addition, three laboratory experiments were conducted to optimize a time period for S. feltiae field application. (1) Abundance of fly larvae inside fallen olives was estimated over the 2006–2007 season with the highest number of susceptible larvae (3 mm and larger) per 100 olives being observed during December, 2006. (2) S. feltiae efficacy against fly larvae dropped to the soil post-IJ-application was determined. B. oleae added to the substrate before and after nematode application were infected at similar levels. (3) Effect of three temperature regimes (min–max: 10–27, 6–18, and 3–12 °C) corresponding to October through December in Davis, California on S. feltiae survival and infectivity was determined. After 8 weeks, the IJs at the 3–12 °C treatment showed the highest survival rate. However, the cold temperature significantly limited S. feltiae infectivity. Our results demonstrate that B. oleae mature larvae are susceptible to EPN infection both in the soil and within infested olives. Being the most effective species, S. feltiae may have the potential to suppress overwintering populations of B. oleae. We suggest that November is the optimal time for S. feltiae field application in Northern California.     

Overwintering habitat selection by the mummichog, Fundulus Heteroclitus, in a Cape Cod (USA) salt marsh

This study tracked the seasonal distribution and winter habitat selection of the mummichog, Fundulus heteroclitus (Linnaeus), in a Cape Cod, Massachusetts salt marsh. Fish (mean size = 43.1 mm total length, range = 10–93 mm) were collected with a 1 m² throw trap and by excavating sediments. In fall, F. heteroclitus began migrating upstream in creeks and eventually moved into upstream pools where they remained throughout winter. F. heteroclitus burrowed into the sediments of these pools at a density of 0.5 fish m^–2, but was not found burrowed in the sediments of downstream pools or any creeks. Sediments in upstream pools were composed of a higher proportion of fine-grained particles and organic content than other marsh pools and creeks, and winter temperatures in upstream pool sediments remained above 1 °C. Temperatures in the water column and sediments of downstream pools regularly dropped below –1.8 °C, exceeding the lethal limit for F. heteroclitus. These results support other recent work showing that F. heteroclitus migrates upstream in salt marshes in fall and overwinters in salt marsh pools. Moreover, this study demonstrates that F. heteroclitus does not utilize all available pools as overwintering habitat but apparently selects pools with sediments that offer a thermal refuge from lethal winter temperatures.     

Habitat selection of larval brook lampreys (Lampetra planeri,Bloch) in a South Swedish stream

Summary The burrowing larvae of the brook lamprey Lampetra planeri (Bloch) were shown by discriminant analysis to inhabit stream sites having certain qualities. Although a few larvae occurred in far-from-optimal habitats, most larvae selected those with low current velocity, low water depth, a low number of particles in the 0.5–1 mm range, and with low chlorophyll content. Other factors normally positively attributed to larval lamprey distribution such as organic content, shade, and presence of algae did not improve the discriminant model. The last factor even showed a negative correlation. Stream bed stability was considered to be of great importance although it was not possible to estimate quantitatively.     

Factors affecting entomophilic activity of Neoaplectana feltiae in mushroom compost

The host-searching ability of Neoaplectana feltiae Filipjev (= S. bibionis Bovien) (Nematoda: Steinernematidae) in response to larvae of a mushroom fly, Lycoriella solani Winn. was examined in a mushroom substrate. Individuals of L. solani were less attractive for the parasite than larvae of Galleria mellonella L. The nematode juveniles penetrated a 22 cm layer of casing mixture within 2–4 days. In the casing alone nematode effectiveness was better than in mushroom compost or in compost and casing together. In the casing mixture parasite dosages of 20 and 100 juveniles per cm² led to 22% and 45% parasitization of L. solani respectively, while all G. mellonella larvae were parasitized at both dosages. The prevalence of nematode infection depended on the content of water in the mushroom substrate. The highest N. feltiae infectivity was observed, when the ratio of the dry casing weight to the weight of water content was 1: 2.5. The practical aspects of the observed phenomena, essential for the use of N. feltiae in the protection of commercial mushroom cultivation are discussed.     

Changes in biochemical composition and energy utilization during metamorphosis of leptocephalous larvae of the bonefish (Albula)

Synopsis Energy use and changes in whole-body content of lipid, protein, nitrogen, carbohydrate and ash were followed during metamorphosis of leptocephalous larvae of the bonefish (Albula). During metamorphosis, which requires about 8–12 days, larvae lost about 3–4 mg of lipid, or about 50% of the total lipid content. Lipid levels, calculated on a dry weight basis, showed no discernible trends, with values ranging from 138–185 mg (g dry wt)^–1. Protein content was 8.4 mg per larva and showed no significant change. However, protein levels increased from 147 to 329 mg (g dry wt)^–1. Nitrogen content decreased slightly from about 3.5 to 3.2 mg per larva. A comparison of protein and nitrogen values, expressed as % dry weight, showed that, in larvae which were just beginning to metamorphose, 70% of the total nitrogen was non-protein nitrogen (NPN). The NPN decreased to 58% of the total nitrogen towards the end of metamorphosis. Carbohydrate content fell from about 3.5 to 0.6 mg per larva, which represents an 83% loss. Carbohydrate levels also fell from about 81 to 32 mg (g dry wt)^–1. In addition, most of the carbohydrate appears to be bound to protein. Ash content decreased by 52%, from 4.6 to 2.2 mg per larva. Caloric content fell slightly from about 182 to 141 calories per larva whereas caloric density showed no discernible trends, with values ranging from 4.180 to 4.725 kcal (g dry wt)^–1. These results indicate that metamorphosing leptocephali, which apparently do not feed, probably derive most of their energy requirements from metabolizing endogenous lipid and carbohydrate stores formed during the premetamorphic interval.     

Food preferences of tanypodinae larvae (Diptera: Chironomidae)

Analyses of the gut contents of larvae of three species of Tanypodinae, collected from four sites in north-east England and Scotland, invariably showed small particles (1–10 µm²), predominantly of detritus, to be more abundant than large particles (10–100 µm²), mostly algae and diatoms. No animal remains, such as carapaces, head capsules and chaetae, or vascular plant fragments were found in any of the intestines. In contrast, food-choice and growth experiments suggested that animal food (particularly Tubificidae and Chironominae larvae) was important in the tanypod diet. In the food-choice experiments, six different foods offered to small (4–7 mm long) and to large (8–12 mm long) larvae of Procladius choreus Meigen, were chosen in the following order: live Tubificidae spp.; detritus; live Chironominae larvae; a mixture of algae and diatoms; live Ostracoda spp.; and live Cladocera spp. However, when the results of the individual choices were examined, it was clear that the small larvae had consumed greater amounts of the small types of food (i.e. detritus, algae and diatoms) in comparison to the large larvae. In the growth experiment, those larvae of P. choreus reared solely on Tubificidae, detritus or Chironominae larvae thrived, while those fed on algae and diatoms, ostracods or cladocerans grew more slowly and fewer survived the experimental period.It was concluded that although Tanypodinae larvae are primarily predators with definite food preferences in ideal foraging conditions, in adverse conditions they will utilize a range of available stand-by foods, the most important of which appears to be detritus.     

Growth and habitat separation in eight cohorts of three species of cyprinids in a subalpine lake

Synopsis Distribution and growth of the embryos, larvae and juveniles of Rutilus rutilus (roach), Scardinius erythrophthalmus (rudd) and Leuciscus cephalus (chub) from an oligotrophic subalpine lake in Tyrol, Austria, were studied during the first three to four months after hatching. R. rutilus was the first to spawn, a single cohort hatching around May 23rd. Four cohorts of S. erythrophthalmus hatched between June 19 and August 1. Three cohorts of L. cephalus hatched between July 3 and 25. The length/weight relationship of all species changed at a length of approximately 15–16 mm. R. rutilus, hatching at the lowest temperature, also showed the lowest growth rate during early life (maximum 10.4 per cent fresh body weight day^–1). In the other two species relative growth rates up to 20% day^–1) were measured. Rudd and chub remained in the shallow littoral during the whole period of observation, whereas roach left the littoral a few weeks after hatching and migrated into deeper water. A subtle shift in vertical distribution was observed for the first cohort of rudd which moved into slightly deeper water when the second cohort made its appearance.To whom correspondence should be addressed