Yolk utilization and growth to yolk-sac absorption in summer flounder (Paralichthys dentatus) larvae at constant and cyclic temperatures

Rates of development, growth and yolk conversion efficiency were determined in larvae of the summer flounder Paralichtys dentatus at constant temperatures of 21°, 16°, 12° and 5°C and in temperature cycles of 21°–16°, 16°–11°, and 11°–5°C. In constant incubation temperatures, development rate increased with increasing temperature. Larvae reared in the cyclic temperature regimes exhibited development rates intermediate to those at the temperature extremes of the cycle. All larvae reared at 5°C and in the 11°–5°C cycle regime died prior to total yolk-sac absorption. Although development rates were temperature dependent, no significant differences in notochord length ash-free dry weight or yolk utilization efficiency were found at the time of total yolk-sac absorption. The similarity in growth and yolk utilization efficiency for larvae reared under these various temperature regimes suggests that the physiological mechanisms involved are able to compensate for temperature changes encountered in nature.Contribution No. 195 from EPA, Environmental Research Laboratory, Narragansett, Rhode Island 02882, USA     

Effects of delayed feeding and temperature on the age of irreversible starvation and on the rates of growth and mortality of Pacific herring larvae

The time periods from exhausion of the yolk to the age of irreversible starvation for Pacific herring Clupea harengus pallasi larvae were 8.5, 7.0 and 6.0 d at 6°, 8° and 10°C, respectively. These periods are within the range perviously measured for Atlantic herring larvae and other temperature zone fish species; they are long compared to the periods for tropical species. The variation in the length of this period is due almost entirely to temperature; the natural logarithm of the time period from fertilization to irreversible starvation is highly correlated (r=0.91) with the mean rearing temperature for 25 species of pelagic marine fish larvae. The rates of growth and mortality, measured for 26 experimental populations of Pacific herring larvae reared at 6°, 8° and 10°C and ten ages of delayed first feeding, decreased and increased, respectively with increasing age of first feeding and increasing temperature. These rates, adjusted for the effects of rearing conditions, were compared with the rates for natural populations of herring larvae. Growth is generally faster in the sea than in experimental enclosures. Two of the eleven estimates of natural mortality rate were high enough to indicate possible catastrophic mass starvation. This is consistent with Hjort's critical period concept of year class formation and it suggests that mass starvation occurs in 18 to 36% of the natural populations of first feeding herring larvae.     

Effects of temperature on oxygen consumption,growth, and development of embryos and yolk-sac larvae of Siganus randalli (Pisces: Siganidae)

Eggs from laboratory spawnings of the coralreef fish Siganus randalli Woodland were incubated at two temperatures (27 and 30 °C). Eggs and larvae were sampled until larval starvation, while changes in oxygen consumption, growth, yolk utilization, and development were monitored. Oxygen consumption, which peaked at hatching, was higher for embryos incubated at 30 °C than at 27 °C. Rates of oxygen consumption (nl h^-1 individual^-1) at hatching were similar to those for other temperate and tropical species. Rates of oxygen consumption by yolk-sac larvae were highly variable, and these data suggest that larval oxygen consumption prior to yolk-sac absorption may not be significantly influenced by temperature. Rates of yolk depletion were higher for larvae at the higher temperature. After an initial rapid increase in length, length of larvae at 30 °C decreased with age. Egg size, egg weight, and maximum notochord length of larvae differed significantly between spawns. Age-specific oxygen consumption rates by the embryos varied between spawns, but regressions describing oxygen consumption as a function of age did not differ significantly. The initiation and completion of eye pigmentation were used as developmental markers to calculate the amount of yolk remaining for larvae at the different temperatures. Larvae maintained at 30 °C completed eye pigmentation approximately 3 h sooner than those maintained at 27 °C, but had less endogenous reserves. This finding indicates a trade-off between rapid development and efficient utilization of the endogenous reserves. The completion of eye pigmentation in larvae incubated at the higher temperature occurred at midnight and, depending on the amount of time that the larvae have to initiate feeding prior to the point-of-no-return, the timing of completion of eye pigmentation could influence larval survival.     

Suitability of estuarine nursery zones for juvenile weakfish (Cynoscion regalis): effects of temperature and salinity on feeding,growth and survival

Juvenile weakfish, Cynoscion regalis (Bloch and Schneider, 1801), exhibit significant spatial diffrences in growth rate and condition factor among estuarine nursery zones in Delaware Bay. The potential influence of temperature and salinity on the suitability of estuarine nursery areas for juvenile weakfish was investigated in laboratory experiments by measuring ad libitum feeding rate, growth rate and gross growth efficiency of juveniles collected in Delaware Bay in 1990 (40 to 50 mm standard length; 1.4 to 2.1 g) in 12 temperature/salinity treatments (temperatures: 20, 24, 28°C; salinities: 5, 12, 19, 26 ppt) representing conditions encountered in different estuarine zones during spring/summer. Feeding rates (FR) increased significantly with temperature at all salinities, ranging from 10 to 15% body wt d^-1 at 20°C to 33–39% body wt d^-1 at 28°C. Specific growth rates (SGR) ranged from 1.4 to 9.4% body wt d^-1 (0.3 to 1.5 mm d^-1) and gross growth efficiencies (K ₁) varied from 13.6 to 26.4% across temperature/salinity combinations. Based on nonlinear multiple regression models, predicted optimal temperatures for SGR and K ₁ were 29 and 27°C, respectively. Salinity effects on SGR and K ₁ were significant at 24 and 28°C where predicted optimal salinity was 20 ppt. At these warmer temperatures, SGR and K ₁ were significantly lower at 5 than at 19 ppt despite higher FR at 5 ppt. Therefore, maximum growth rate and growth efficiency occurred under conditions characteristic of mesohaline nurseries. This finding is consistent with spatial patterns of growth in Delaware Bay, implying that physicochemical gradients influence the value of particular estuarine zones as nurseries for juvenile weakfish by affecting the energetics of feeding and growth. Laboratory results indicate a seasonal shift in the location of physiologically optimal nurseries within estuaries. During late spring/early summer, warmer temperatures in oligohaline areas permit higher feeding rate and faster growth compared to mesohaline areas. By mid-late summer, spatial temperature gradients diminish and mesohaline areas provide more suitable physicochemical conditions for growth rate and growth efficiency whereas oligohaline areas become energetically stressful. Substantial mortality occurred at 5 ppt and 28°C, providing additional evidence that oligohaline conditions are stressful during late summer. Furthermore, juveniles provided a choice among salinities in laboratory trials preferred those salinities which promoted higher growth rates. The extensive use of oligohaline nurseries by juvenile weakfish despite the potential for reduced growth rate and growth efficiency suggests this estuarine zone may provide a substantial refuge from predation.     

Feeding of laboratory-reared larvae of the sea bream Archosargus rhomboidalis (Sparidae)

Feeding by larvae of the sea bream Archosargus rhomboidalis (Linnaeus) was investigated from late September, 1972 to early May, 1973 using laboratory-reared larvae. Fertilized eggs were collected from plankton tows in Biscayne Bay, and the larvae were reared on zooplankton also collected in plankton nets. Techniques were developed to estimate feeding rate, food selection, gross growth efficiency, and daily ration. Daily estimates of these were obtained through 16 days after hatching at rearing temperatures of 23°, 26°, and 29°C. Feeding rate increased exponentially as the larvae grew, and increased as temperature was raised. At 23°C larvae began feeding on Day 3, at 26° and 29°C larvae began feeding on Day 2. Feeding rates at initiation of feeding and on Day 16 were, respectively: 23°C, 7.16 food organisms per larva per hour (flh) and 53.78 flh; 26°C, 7.90 flh and 168.80 flh; 29°C, 17.62 flh and 142.07 flh. Sea bream larvae selected food organisms by size. At initiation of feeding they selected organisms less than 100 m in width. As larvae grew they selected larger organisms and rejected smaller ones. The major food (more than85% of the organisms ingested) was copepod nauplii, copepodites, and copepod adults. Minor food items were barnacle nauplii, tintinnids, invertebrate eggs, and polychaete larvae. Mean values for gross growth efficiency of sea bream larvae ranged from 30.6% at 23°C to 23.9% at 29°C. Mean values for daily ration, expressed as a percentage of larval weight, ranged from 84% at 23°C to 151% at 29°C and tended to decline as the larvae grew.This paper is a contribution from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA     

Effects of temperature on morphological landmarks critical to growth and survival in larval Atlantic cod (Gadus morhua)

The morphology and function of structures important to energy acquisition were studied from spawning to the stage of transformation of larva to pelagic juvenile in Atlantic cod, Gadus morhua L., from December 1991 to July 1992. Fertilized eggs produced by adult fish from two genetically discrete populations (Newfoundland and Scotian Shelf) were raised under similar conditions in the laboratory at temperatures of 5 and 10°C. Subsamples of larvae were removed from cultures daily for 10 d, and then less frequently, and fixed for light microscopy and scanning electron microscopy. Nine functional morphological landmarks important to feeding, respiration and locomotion were chosen from observation of 280 ind. These landmarks defined 12 major developmental stages, from hatching to the pelagic juvenile stage. One of the feeding landmarks, intestinal stage, varied as a function of age and size and the variance in development was higher at 10°C than at 5°C; Newfoundland larvae developed more complex intestines than did Scotian Shelf larvae. In addition, Newfoundland larvae had significantly higher growth rates than those of Scotian Shelf larvae. Despite the higher growth rates and greater structural complexity of the intestine in Newfoundland larvae, the rate of yolk utilization was not significantly different between Newfoundland and Scotian Shelf larvae. Staging of respiratory landmarks showed that the gill arches were probably used preferentially in feeding while respiration was cutaneous. The gills, operculum and gill rakers developed late in larval life and accompanied the transition from cutaneous to branchial respiration. In the yolk-sac period, development of feeding and respiratory structures may be largely genetically controlled. During exogenous feeding, extrinsic factors also become important, as shown by the size and age-independent variation in intestinal development of larval cod raised at different temperatures.     

Effect of temperature on the escape responses of larval herring,Clupea harengus

Herring (Clupea harengus L.) larvae from spring and autumn spawning stocks were reared at different constant temperatures from 5° to 17 °C. At equivalent developmental stages, the spring larvae were longer than the autumn larvae and the larvae reared at low temperatures were longer than those reared at high temperatures. At hatching and at the end of the yolk-sac stage, the larvae were induced, by a probe, to make C-start escape responses, which were recorded and analysed using a high-speed video recording at 400 frames s^-1. The response was rapid and of short duration. The tailbeat frequency and swimming speed were measured during the burst of swimming following the C-start at different test temperatures and in larvae with different temperature histories. The tail-beat frequency was strongly temperature-dependent, rising from 19 Hz at 5 °C to 37 Hz at 17 °C with no effect of temperature history, season or developmental stage. The burst-swimming speed ranged at hatching from 75 to 90 mm s^-1 at 5 °C to 110 to 160 mm s^-1 at 17 °C and at yolk resorption from 90–115 mm s^-1 at 5 °C to 175–190 mm s^-1 at 17 °C. The longer, spring-spawned larvae swam faster than the shorter autumn-spawned larvae. When the swimming speeds were expressed as body lengths (L) s^-1, these differences disappeared. Larvae swam from 7–9 L s^-1 at 5 °C to 15–20 L s^-1 at 17 °C at hatching, and from 8–9 L s^-1 at 5 °C to 15–17 L s^-1 at 17 °C at yolk resorption. There was, however, a significantly faster specific swimming speed by the larvae reared at 12 °C in spring 1991.Honorary Research Fellow of the Scottish Association for Marine ScienceUnfortunately, Karen Fretwell was drowned in an accident on 9 January 1993     

Feeding energetics and metabolism in demersal fish species from Antarctic,temperate and tropical environments

The energetics of feeding has been investigated in demersal fish with similar sedentary lifestyles from the Antarctic (Notothenia neglecta Nybelin), North Sea (Myoxocephalus scorpius L.) and Indian Ocean (Cirrhitichys bleekeri Bleeker). In general, the metabolic rates of fasting individuals were positively correlated with adaptation temperature: values for a standard 100 g fish (mg O₂/h) were 3.3 for N. neglecta at around 0 °C, 2.7 for winter-acclimatized M. scorpius at 5 °C, 4.3 for summer-acclimatized M. scorpius at 15 °C, and 7.0 for C. bleekeri at 25 °C. In all species, following a single satiating meal, oxygen consumption increased to a peak of 2 to 3.5 times the fasting values. Maximum rates of oxygen consumption after feeding were several-fold higher in the warm-than in the cold-water species. After controlling for the effects of body mass and energy intake by analysis of covariance, the duration of the increase in metabolic rate, referred to as specific dynamic action (SDA), was found to be 3 to 4 times shorter in the warm- than in the cold-water fish, ranging from 57 h in C. bleekeri to 208 h in N. neglecta. In contrast, the SDA was not significantly different in the various species, corresponding to 15 to 23% of the energy ingested. Seasonal influences on metabolism and feeding were also studied in N. neglecta acclimated to simulated winter (-1.0 to-0.5 °C; 3 h light:21 h dark) or summer (0 to 0.9 °C; 21 h light:3 h dark) conditions. The metabolic rates of fasting and fed individuals, and the characteristics of the SDA were found to be independent of acclimation conditions. This suggests that N. neglecta is capable of processing food at similar rates throughout the year. Energy stores and enzyme activities were measured in the swimming muscles and liver of fish fed ad libitum. Summer-acclimated fish had higher concentrations of liver triglyceride stores and elevated activities of some enzymes of intermediary metabolism relative to winter-acclimated fish. The observed changes in intermdiary metabolism are probably related to annual cycles of growth and reproduction. It is suggested that the low aerobic scope for physiological performance in Antarctic fish may necessitate the seasonal switching of energy allocation between growth and reproduction.     

Effects of nutrition and temperature on metabolic enzyme activities in larval and juvenile red drum,Sciaenops ocellatus,and lane snapper,Lutjanus synagris

The metabolic enzyme activities were determined in larvae of red drum, Sciaenops ocellatus, and lane snapper, Lutjanus synagris, to determine the effect of temperature and nutrition on metabolic enzyme activities and to evaluate if metabolic enzyme activities are useful in assessing the feeding condition of larval fish. During experiments conducted during the spring of 1990, lactate dehydrogenase (LDH) activities in both red drum and lane snapper were approximately an order of magnitude lower than values typical for adult fish; LDH and citrate synthase (CS) activities increased during early developmental stages, but nutritional effects were apparent. Clear differences (up to 4-fold) between well-fed and starving fish were evident in both LDH and CS activity in red drum. Differences between well-fed and poorly fed larvae were evident until 9 d after hatching. Lane snapper larvae reared at a 25°C had significantly lower LDH activities than larvae reared at 28°C.     

Yolk resorption,onset of feeding and survival potential of larvae of three tropical marine fish species reared in the hatchery

This paper provides basic early life-history information on milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) which may explain in part the observed differences in their survival performance in the hatchery. Egg size, larval size, amount of yolk and oil reserves and mouth size are all greater in milkfish than in seabass, and greater in the latter than in rabbitfish. During the first 24 h after hatching, rabbitfish larvae grow much faster than milkfish and seabass larvae at similar ambient temperatures (range 26°–30°C, mean about 28°C). The eyes become fully pigmented and the mouths open earlier in seabass and rabbitfish (32–36 h from hatching) than in milkfish (54 h). Seabass larvae learn to feed the earliest. Yolk is completely resorbed at 120 h from hatching in milkfish, and yolk plus oil at 120 h in seabass and 72 h in rabbitfish at 26° to 30°C. Milkfish and seabass larvae have more time than rabbitfish to initiate external feeding before the endogenous reserves are completely resorbed. Delayed feeding experiments showed that 50% of unfed milkfish larvae die at 78 h and all die at 150 h from hatching. Milkfish larvae fed within 54 to 78 h after hatching had improved survival times: 50% mortality occurred at 96 to 120 h, and 10 to 13% survived beyond 150 h. Unfed seabass larvae all died at 144 h, while 6 to 13% of those fed within 32 to 56 h after hatching survived beyond 144 h and well into the subsequent weeks. Unfed rabbitfish larvae all died at 88 h, while 7 to 12% of those fed within 32 to 56 h after hatching survived beyond 88 h. A delay in initial feeding of more than 24 h after eye pigmentation and opening of the mouth may be fatal for all three species.Contribution No. 167 from the SEAFDEC Aquaculture Department     

The use of RNA:DNA ratios to predict growth limitation of juvenile summer flounder (Paralichthys dentatus) from Delaware and North Carolina estuaries

Nutritional indices were used to develop biochemical correlates of feeding and growth rates for juvenile summer flounder, Paralichthys dentatus (Linnaeus), from North Carolina (NC) and Delaware (DE). Six parameters (Fulton's condition K=10⁴xweight/(length³), wet weight/dry weight, [protein], [RNA], [DNA], and RNA:DNA) were related to feeding and growth rates of fish from previously reported 10 to 14-d experiments at temperatures ranging from 2 to 20 °C with varying feeding levels (0 to 100% and libitum). RNA:DNA ratios were the best predictors of growth rates, but inclusion of a temperature term improved the relationship between RNA:DNA ratios and growth rate for Delaware fish. Feeding rates were poorly correlated with all parameters. RNA:DNA ratios of fish in the laboratory changed significantly within 1 d of starvation and refeeding at 16 °C. RNA:DNA of juvenile summer flounder collected from one site in Indian River Bay, DE and two sites in the Newport River Estuary, NC, between January and June 1992 were used to estimate in situ growth rates following settlement. Predicted growth rates in both estuaries were close to maximum (suggesting ad libitum feeding) until early May. Growth rates of juveniles from Delaware were <0% d^-1 from December through early March, and were higher (0.6 to 3% d^-1) from April through early June. However, growth rates of DE juveniles during May were <50% of maxinum. North Carolina juveniles had growth rates of 2 to 5% d^-1 from February through early April. Juveniles from one of the Newport River sites (a marsh habitat) were also severely growth limited (<20% of maximum) after April. Prolonged periods of sub-optimal growth may be important to survival and recruitment of juvenile summer flounder in northern mid-Atlantic estuaries. A model is presented which illustrates the potential impact that small changes in temperature and growth limitation can have on recruitment success in both delaware and North Carolina estuaries.     

A dispersal model for larvae of the deep sea red crab Geryon quinquedens based upon behavioral regulation of vertical migration in the hatching stage

Behavioral responses to gravity, hydrostatic pressure, and thermoclines are described for Stage I zoeae of the deep sea red crab Geryon quinquedens Smith. Survival and rate of development as a function of temperature is presented for all larval stages. Although temperatures between 10° and 25°C have no direct effect upon survival, development time is five times longer at 10°C than at 25°C. Stage I larvae show strong negative response to gravity. Swimming rate increases with an increase in pressure up to 20 atm above ambient at 11°C, but not at 15°C. Swimming rates at 15°C are higher than those measured at 11°C at each pressure tested. Stage I larvae readily penetrate sharp thermoclines. Potential dispersal ranges of G. quinquedens larvae in the Mid-Atlantic Bight are suggested based on larval behavior, development time, and coastal hydrography. A testable recruitment model is proposed for G. quinquedens.Contribution no. 1365 of the Center for Environmental and Estuarine Studies     

Temperature influences muscle differentiation and the relative timing of organogenesis in herring (Clupea harengus) larvae

Eggs from spring spawning stocks of herring (Clupea harengus L.) were fertilized and reared at either 5, 8 or 12°C in 1991 and 1992. The differentiation of myotomal muscle fibres was investigated in relation to the development of other organs and tissues using light and electron microscopy. The gut, notochord, eyes and haemocoel appeared at the same relative point in development between fertilization and hatching at all temperatures. In contrast, the formation of the spinal cord, pronephros, pectoral fin buds and muscle fibres was relatively retarded at 5°C compared with 8 and 12°C. Myogenesis in the presumptive inner muscle mass occurred after 12 to 16 d at 5°C, 7 to 10 d at 8°C and 3.5 to 6 d at 12°C. Myoblasts aligned in orderly rows running from myosept to myosept prior to fusion to form myotubes. Actin and myosin filaments were synthesised throughout the cytoplasm in associated with presumptive Z-lines at the periphery of myotubes and immature muscle fibres. Differentiation of the superficial and inner muscle fibres types of larvae occurred at around the same time. Following this initial period of myogenesis, the number of myotomal muscle fibres remained constant until after hatching, so that increases in muscle bulk in the late embryo were entirely due to fibre hypertrophy. At hatching, the number of superficial muscle fibres present in myotomes just posterior to the yolk-sac was significantly less at 5°C (108±12) than at either 8°C (132±10) or 12°C (140±10) (mean±SD, 12 fish/temperature). In contrast, there were around 280 inner muscle fibres/myotome, comprising 90% of the trunk cross-sectional area, at all three temperatures. Myofibrillargenesis occurred relatively slowly at low temperatures, so that the volume density of myofibrils in the inner muscle fibres of larvae at hatching was significantly less at 5°C (39.2±9.0) than at either 8°C (49.6±8.8) or 12°C (50.2±9.8) (mean ±SD, 20 fibres/temperature from total of 5 fish). Undifferentiated myoblasts remained at hatching to form a population of presumptive myosatellite cells. The number of presumptive myosatellite cells per mm² cross-sectional area of muscle fibre was more than two times higher at 8°C (1493±335) than at either 5°C (478±102) or 12°C (924±233) (mean±SD, 5 fish/temperature). The results suggest that temperature can influence the commitment of myoblasts to differentiation at a critical stage in embryogenesis, thereby providing a potential mechanism for influencing future growth characteristics. Correspondence to: I.A. Johnston at Gatty Marine Laboratory     

Effect of temperature on the egg and yolk-sac larval development of common pandora,<Emphasis Type="Italic"> Pagellus erythrinus</Emphasis>

Temperature is one of the most critical environmental factors for fish ontogeny, affecting the developmental rate, survival and phenotypic plasticity in both a species- and stage-specific way. In the present paper we studied the egg and yolk-sac larval development of Pagellus erythrinus under different water temperature conditions, 15°C, 18°C and 21°C for the egg stage and 16°C, 18°C and 21°C for the yolk-sac larval stage. The temperature-independent thermal sum of development was estimated as 555.6 degree-hours above the threshold temperature (the temperature below which development is arrested), i.e. 7°C for the egg and 12.1°C for the yolk-sac larval stage. Higher hatching and survival rates occurred at 18–21°C. At the end of the yolk-sac larval stage, body morphometry differed significantly (p<0.05) between the temperatures tested. The growth rate of the total length increased as temperature rose from 16°C to 18°C, while in the range of 18–21°C it stabilized and was independent of water temperature. The estimated Gompertz growth curve for the yolk-sac larvae of P. erythrinus was (r²=0.992) for the 16°C, (r²=0.991) for the 18°C and (r²=0.981) for the 21°C treatment. The efficiency of vitelline utilization during the yolk-sac larval stage was higher at 18°C.Communicated by O. Kinne, Oldendorf/Luhe     

Rearing<Emphasis Type="Italic"> Pandalus borealis</Emphasis> (Krøyer) larvae in the laboratory

Northern shrimp Pandalus borealis (Krøyer) larvae hatch in the northern Gulf of St. Lawrence from early May to the end of June, and larval development occurs over a range of relatively cold water temperatures. Because of the long duration of the pelagic phase and the difficulty of sampling all successive larval stages at sea, we used laboratory experiments to assess the effects of water temperature on larval development and growth. In spring 2000, P. borealis larvae were reared from hatching to the first juvenile stages (i.e., stage VI and VII) at three temperatures (3, 5, and 8°C) representing conditions similar to those in spring in the northern Gulf of St. Lawrence. Larval development and growth were dependent on temperature, with longer duration and smaller size (cephalothorax length, CL, and dry mass, DM) at 3°C relative to the 5 and 8°C treatments. There were no significant differences in the morphological characters of the different stages among treatments, indicating that regular moults occurred at each temperature. The results suggest a negative impact of cold temperatures (lower intra-moult growth rates and smaller size) and, possibly, higher cumulative mortality due to longer development time that could affect the success of cohorts at sea. However, CL and DM for stage III and later larvae were smaller than those of larvae identified at the same developmental stage in field locations. It is possible that the diet offered to larvae in this experiment (Artemia nauplii, either newly hatched nauplii or live adults, depending on the developmental stage) was not optimal for growth, even though it is known to support successful P. borealis larval development. In the field, there is the possibility that phytoplankton contributes to the larval diet during the first stages and stimulates development of the digestive glands. Furthermore, the nutritional quality of the natural plankton diet (e.g., high protein content, fatty acid composition) might be superior and favourable to higher growth rates even at lower temperatures.Communicated by R.J. Thompson, St. Johns     

Growth rate and reproductive differences in a widespread estuarine harpacticoid copepod (Scottolana canadensis)

We demonstrate the presence of significant genetically based differentiation in growth rate (g dry weight d^-1) and reproductive traits (percent reproductive females and mean clutch size g dry weight^-1) among females of an harpacticoid copepod (Crustacea),Scottolana canadensis (Willey), taken from a broad range of latitudes and reared in the laboratory under the same conditions. As temperature increases (15°–25° C), the growth rate of southern-derived copepods continues to increase, while that of northern-derived copepods levels off or decreases. Southern-derivedS. canadensis also have a higher percentage of reproducing females at high temperature (25°C) when rations (cells ml^-1) are reduced, while northern-derived females are at an advantage at low temperature (15°C). Both life-history traits indicate local adaptation to maximize scope for growth and reproduction at prevailing temperatures. The data support our hypothesis that evolution has occurred to maximize feeding minus metabolic energy expended, and that this maximization requires changes in feeding efficiency with differing temperatures.     

Effect of temperature on specific dynamic action in the common octopus,<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> (Cephalopoda)

Feeding causes an increase of metabolic rate, which initially escalates rapidly, reaches a peak value and then gradually declines to the pre-feeding rate. This phenomenon, termed specific dynamic action (SDA), reflects the energy requirements of the behavioral, physiological and biochemical processes that constitute feeding. The effect of temperature on SDA of the common octopus, Octopus vulgaris, was evaluated, by measuring the temporal pattern of the oxygen consumption rates of octopuses, after feeding, at two constant temperatures, 20°C and 28°C. At 20°C, the relative increase in the oxygen consumption rate after feeding (relative SDA) was significantly greater than at 28°C. The peak of the relative SDA occurred 1 h after feeding, and it was 64% at 20°C and 42% at 28°C. However, the SDA absolute peak, SDA duration (9.5 h) and SDA magnitude (the integrated postprandial increase in oxygen uptake) did not differ significantly between the two temperatures, indicating that the energetic cost of feeding was the same at both temperatures. The SDA response in O. vulgaris was much faster than it was in polar species, which have extended SDA responses due to low temperatures, and was also relatively fast in relation to the response in other temperate species, which is probably connected to the remarkably high growth rates of the species. A possible explanation of the observed summer migration of large octopuses from shallow to deeper areas is given, based on the effect of temperature on the energetic requirements of octopuses.     

Egg survival,embryonic development,and larval characteristics of northern shrimp (<Emphasis Type="Italic">Pandalus borealis</Emphasis>) females subject to different temperature and feeding conditions

Laboratory experiments on ovigerous females of northern shrimp (Pandalus borealis) were used to assess the effects of temperature and food ration on female condition during incubation and examine how combined effects of temperature and female condition influenced egg survival, embryonic development, and larval characteristics. Ovigerous females were maintained at 2°C, 5°C, and 8°C and fed on a low (three times/week; 2–2.7% W/W) or high ration (five times/week at satiation). The increase in temperature accelerated the developmental time of the eggs but their survival at 8°C was reduced. Conversion efficiency of yolk reserves in developing embryos was significantly reduced at elevated temperatures and larvae hatching at 2°C and 5°C were significantly larger and heavier than those hatching at 8°C. The experimental design did not result in any effect of food ration on the energetic condition of females or on egg characteristics and their biochemical composition. However, lower energy reserves were observed for females held at 8°C.     

Embryogenesis and larval biology of the ahermatypic scleractinian<Emphasis Type="Italic"> Oculina varicosa</Emphasis>

The ivory tree coral Oculina varicosa (Leseur, 1820) is an ahermatypic branching scleractinian that colonizes limestone ledges at depths of 6–100 m along the Atlantic coast of Florida. This paper describes the development of embryos and larvae from shallow-water O. varicosa, collected at 6–8 m depth in July 1999 off Fort Pierce, Florida (27°32.542 N; 79°58.732 W). The effect of temperature on embryogenesis, larval survival, and larval swimming speed were examined in the laboratory. Ontogenetic changes in geotaxis and phototaxis were also investigated. Embryos developed via spiral cleavage from small (100 µm), negatively buoyant eggs. Ciliated larvae developed after 6–9 h at 25°C. Embryogenesis ceased at 10°C, was inhibited at 17°C, and progressed normally at 25°C and 30°C. Larval survival, however, was high across the full range of experimental temperatures (11–31°C), although mortality increased in the warmest treatments (26°C and 31°C). Larval swimming speed was highest at 25°C, and lower at the temperature extremes (5°C and 35°C). An ontogenetic change in geotaxis was observed; newly ciliated larvae swam to the water surface and remained there for approximately 18 h, after which they swam briefly throughout the water column, then became demersal. Early larvae showed no response to light stimulation, but at 14 and 23 days larvae appeared to exhibit negatively phototactic behavior. Although low temperatures inhibited the development of O. varicosa embryos, the larvae survived temperature extremes for extended periods of time. Ontogenetic changes in larval behavior may ensure that competent larvae are close to the benthos to facilitate settlement. Previous experiments on survival, swimming speeds, and observations on behavior of O. varicosa larvae from deep-water adults indicate that there is no difference between larvae of the deep and shallow populations.Communicated by J.P. Grassle, New Brunswick     

Rearing Pandalus borealis larvae in the laboratory

Larvae of the northern shrimp Pandalus borealis (Krøyer) are pelagic. In the Estuary and Gulf of St. Lawrence, Canada, the early stages are found in the upper 25-m of the water column in spring and early summer and are expected to experience a range of water temperatures from as low as 0°C to as high at 6°C. Little is known of the impact of water temperature on metabolic requirements of northern shrimp larvae. In this study, routine respiration (VO₂), maximum respiration (electron transport system activity, ETSA) and metabolic scope for growth (MS, ETSA–VO₂) of northern shrimp larvae were measured as a function of temperature (3, 5 and 8°C), developmental stage (I–V at 3°C, I–VII at 5°C and 8°C) and growth rate in dry mass. After logarithmic transformation, all three metabolic variables were linearly related to dry mass. The increase in VO₂ with body mass was faster at 5°C than at 3 or 8°C, whereas with ETSA this increase was slower. As a result, MS increased more slowly with dry mass at 5°C than at 3 and 8°C. However, MS did not limit growth in this study, since it explained only 39% of the variability in growth. All three metabolic variables as well as growth varied together as a function of temperature and ontogeny. Q₁₀ of all three metabolic variables ranged from 1.6 and 2.2 for stages I–V larvae, except for VO₂ at stage I (3.9) and stage III (2.9).