The mechanical effects of water flow on fish eggs and larvae

The impact of mechanical stresses upon ichthyoplankton entrained in power plant cooling systems has long been considered negligible. Arguments and evidence exist, however, to show that such a supposition is not universally true, especially in nuclear power plants. The mechanisms of mechanical damage can be detailed in terms of pressure change, acceleration, and shear stress with in the fluid flow field. Laboratory efforts to quantify the effects of mechanical stress have been very sparse. A well-planned bioassay is urgently needed. (PDF has 11 pages.)

Effects of shear on eggs and larvae of striped bass, morone saxatilis, and white perch, M. americana

Shear stress, generated by water movement, can kill fish eggs and larvae by causing rotation or deformation. Through the use of an experimental apparatus, a series of shear (as dynes/cm2)-mortality equations for fixed time exposures were generated for striped bass and white perch eggs and larvae. Exposure of striped bass eggs to a shear level of 350 dynes/cm2 kills 36% of the eggs in 1 min; 69% in 2 min, and 88% in 4 min; exposure of larvae to 350 dynes/cm2 kills 9.3% in 1 min, 30.0% in 2 min, and 68.1% in 4 min. A shear level of 350 dynes/cm2 kills 38% of the white perch eggs in 1 min, 41% in 2 min, 89% in 5 min, 96% in 10 min, and 98% in 20 min. A shear level of 350 dynes/cm2 applied to white perch larvae destroys 38% of the larvae in 1 min, 52% in 2 min, and 75% in 4 min. Results are experimentally used in conjunction with the determination of shear levels in the Chesapeake and Delaware Canal and ship movement for the estimation of fish egg and larval mortalities in the field.

The ontogeny of haematopoiesis in the marine teleost Leiostomus xanthurus and a comparison of the site of initial haematopoiesis with Opsanus tau

The ontogeny of haematopoiesis in the perciform fish, spot Leiostomus xanthurus, differed from that reported as the norm for fishes, as exemplified by the cypriniform zebrafish Danio rerio, and observed in the batrachoidiform oyster toadfish Opsanus tau. Erythropoiesis in spot was first evident in the head kidney of yolk-sac larvae 3 days after hatching (DAH). No embryonic intermediate cell mass (ICM) of primitive stem cells or blood islands on the yolk were apparent within embryos. Erythrocytes were first evident in circulation near the completion of yolk absorption, c. 5 DAH, when larvae were c. 20 mm notochord length (LN). Erythrocyte abundance increased rapidly with larval development for c. 14 to 16 DAH, then became highly variable following changes in cardiac chamber morphology and volume. Erythrocytic haemoglobin (Hb) was not detected within whole larvae until they were 12 DAH or c. 31 mm LN, well after yolk and oil-globule absorption. The Hb was not quantified until larvae were >47 DAH or >7 mm standard length. The delayed appearance of erythrocytes and Hb in spot was similar to that reported for other marine fishes with small embryos and larvae. In oyster toadfish, a marine teleost that exhibits large embryos and larvae, the ICM and Hb were first evident in two bilateral slips of erythropoietic tissue in the embryos, c. 5 days after fertilization. Soon thereafter, erythrocytes were evident in the heart, and peripheral and vitelline circulation. Initial haematopoiesis in oyster toadfish conformed with that described for zebrafish. While the genes that code for the development of haematopoiesis are conserved among vertebrates, gene expression lacks phylogenetic pattern among fishes and appears to conform more closely with phenotypic expression related to physiological and ecological influences of overall body size and environmental oxygen availability.

Effects of suspended sediments on the development of eggs and larvae of striped bass and white perch

The possible ecological effects of suspended sediments are manifold. Briefly, suspended sediments may cause an increased surface for microorganism growth, fewer temperature fluctuations, chemical adsorption or absorption, blanketing, mechanical-abrasive actions, and light penetration reduction (Cairns, 1968). Sherk and Cronin (1970) have pointed out that the above effects have been little studied in the estuarine environment. The ecological effects of suspended sediments on fish eggs and larvae may be of prime importance t o the C and D Canal area, an important spawning and primary nursery area for a variety of estuary: e species (Johnson,1972). This section discusses the effects of suspended sediment on the eggs and larvae of striped bass and white perch.

Temporal and spatial distribution and abundance of flathead sole (Hippoglossoides elassodon) eggs and larvae in the western Gulf of Alaska

Data from ichthyoplankton surveys conducted in 1972 and from 1977 to 1999 (no data were collected in 1980) by the Alaska Fisheries Science Center (NOAA, NMFS) in the western Gulf of Alaska were used to examine the timing of spawning, geographic distribution and abundance, and the vertical distribution of eggs and larvae of flathead sole (Hippoglossoides elassodon). In the western Gulf of Alaska, flathead sole spawning began in early April and peaked from early to mid-May on the continental shelf. It progressed in a southwesterly direction along the Alaska Peninsula where three main areas of flathead sole spawning were indentified: near the Kenai Peninsula, in Shelikof Strait, and between the Shumagin Islands and Unimak Island. Flathead sole eggs are pelagic, and their depth distribution may be a function of their developmental stage. Data from MOCNESS tows indicated that eggs sink near time of hatching and the larvae rise to the surface to feed. The geographic distribution of larvae followed a pattern similar to the distribution of eggs, only it shifted about one month later. Larval abundance peaked from early to mid-June in the southern portion of Shelikof Strait. Biological and environmental factors may help to retain flathead sole larvae on the continental shelf near their juvenile nursery areas.

Variability in the distribution of planktonic fish eggs and larvae in the nearshore waters off Bombay

Distribution of planktonic fish eggs and larvae in the nearshore waters off Bombay was studied during November 1979 to December 1980. Monthly samples were collected along three transects (Versova, Mahim and Thana) covering eleven stations which represented different environmental conditions. Fish eggs and larvae were common in the area of study with maximum abundance in December 1979 and April/August 1980. Mean density of fish eggs was maximum along the Mahim transect while population of larvae was more in the Versova transect. Total number of families of fish larvae represented in the collections increased from nearshore to offshore area.

Seasonal fluctuation in the distribution of eggs and larvae of flat fishes (Pleuronectiformes - Pisces) in the Cochin backwater

Attempts have been made to correlate the abundance of eggs and larvae of flat fishes belonging to families Cynoglossidae and Soleidae with the hydrographical parameters of the environment, particularly the salinity. The eggs and larvae were found to occur in the Cochin backwater during the pre-monsoon period but not during the south west monsoon period. During the south west monsoon period larvae belonging to very early stages were found at the marine end (Fairway Buoy). The continued or prolonged existence of very low salinity appears to restrict the distribution of flat fish larvae. In the post-monsoon period also the eggs and larvae were not found in regions of very low salinity. Larvae of Cynoglossus puncticeps (Richardson), C. brevis Gunther, C. cynoglossus (Ham. Buch), C. lida (Bleeker) and Solea heinii Steindachner were obtained in the collection taken from the estuary. From the data it is seen that each species has specific spawning period.

Results of drift card experiments and considerations on the movement of milkfish eggs and larvae in the northern Sulu Sea

For a period of one year beginning December 1977, drift card experiments were conducted off the western and southern coasts of Panay Island to determine the surface currents in the area. Of a total 2,384 drift cards released during the study, 382 (16.02%) were recovered, 92% of them within 30 days following dispatch. The surface currents in the study area are strongly influenced, in direction and speed, by the prevailing monsoon winds. During the NE monsoon period, the surface currents move away from the coast; during the SW monsoon, toward and/or parallel to the coast. Based on the results, the probable movement and transport of milkfish (Chanos chanos) eggs and larvae from the spawning ground to the fry collection ground are also discussed.

Studies on the fungal diseases in crustaceans. I. Lagenidum scyllae sp. nov. isolated from cultivated ova and larvae of the mangrove crab (Scylla serrata)

Lagenidium scyllae , a marine mastigomycete from the ova and larvae of the mangrove crab, is described and illustrated as new. The fungus grew at a temperature range of 16-42 C, with an optimum at 22.5-31.8 C. It grew well in peptone-yeast-glucose (PYG) broth containing 2-3% NaCl. In PYG-sea water medium, it grew at a pH range of 5-11.

Effects of maternal age and size on embryonic energy reserves, developmental timing, and fecundity in quillback rockfish (Sebastes maliger)

Maternal effects on the quality of progeny can have direct impacts on population productivity. Rockfish are viviparous and the oil globule size of larvae at parturition has been shown to have direct effects on time until starvation and growth rate. We sampled embryos and preparturition larvae opportunistically from 89 gravid quillback rockfish (Sebastes maliger) in Southeast Alaska. Because the developmental stage and sampling period were correlated with oil globule size, they were treated as covariates in an analysis of maternal age, length, and weight effects on oil globule size. Maternal factors were related to developmental timing for almost all sampling periods, indicating that older, longer, and heavier females develop embryos earlier than younger, shorter, or lighter ones. Oil globule diameter and maternal length and weight were statistically linked, but the relationships may not be biologically significant. Weight-specific fecundity did not increase with maternal size or age, suggesting that reproductive output does not increase more quickly as fish age and grow. Age or size truncation of a rockfish population, in which timing of parturition is related to age and size, could result in a shorter parturition season. This shortening of the parturition season could make the population vulnerable to fluctuating environmental conditions.

The effects of temperature on hatching and survival of northern rock sole larvae (Lepidopsetta polyxystra)

Northern rock sole (Lepidopsetta polyxystra) is a commercially important flatfish in Alaska and was recently classified as a distinct species from southern rock sole (L. bilineata). Taxonomic and vital rate data for northern rock sole are still not fully described, notably at early egg and larval stages. In this study, we provide new taxonomic descriptions of late-stage eggs and newly hatched larvae, as well as temperature-response models of hatching (timing, duration, success), and larval size-at-hatch and posthatch survival at four temperatures (2°, 5°, 9°, and 12°C). Time-to-first-hatch, hatch cycle duration, and overall hatching success showed a negative relationship with temperature. Early hatching larvae within each temperature treatment were smaller and had larger yolk sacs, but larvae incubated at higher temperatures (9° and 12°C) had the largest yolk reserves overall. Despite having smaller yolks, size-at-hatch and the maximum size achieved during the hatching cycle was highest for larvae reared at cold temperatures (2° and 5°C), indicating that endogenous reserves are more efficiently used for growth at these temperatures. In addition, larvae reared at high temperatures died more rapidly in the absence of food despite having more yolk reserves than cold-incubated larvae. Overall, northern rock sole eggs and larvae display early life history traits consistent with coldwater adaptation for winter spawning in the North Pacific.

Ontogenetic patterns and temperature-dependent growth rates in early life stages of Pacific cod (Gadus macrocephalus)

Pacific cod (Gadus macrocephalus) is an important component of fisheries and food webs in the North Pacific Ocean and Bering Sea. However, vital rates of early life stages of this species have yet to be described in detail. We determined the thermal sensitivity of growth rates of embryos, preflexion and postflexion larvae, and postsettlement juveniles. Growth rates (length and mass) at each ontogenetic stage were measured in three replicate tanks at four to five temperatures. Nonlinear regression was used to obtain parameters for independent stage-specific growth functions and a unified size- and temperature-dependent growth function. Specific growth rates increased with temperature at all stages and generally decreased with increases in body size. However, these analyses revealed a departure from a strict size-based allometry in growth patterns, as reduced growth rates were observed among preflexion larvae: the reduction in specific growth rate between embryos and free-swimming larvae was greater than expected based on body size differences. Growth reductions in the preflexion larvae appear to be associated with increased metabolic rates and the transition from endogenous to exogenous feeding. In future studies, experiments should be integrated across life transitions to more clearly define intrinsic ontogenetic and size-dependent growth patterns because these are critical for evaluations of spatial and temporal variation in habitat quality.