Persistent growth effects of temperature and photoperiod in Atlantic cod Gadus morhua

Short-term environmental manipulations during the early juvenile stage have a large impact on harvesting size of Atlantic cod Gadus morhua nearly 3 years later. A group of juvenile Atlantic cod (initial mass 9·5 g) were reared for 3 months under simulated natural photoperiod or continuous light, and a range of temperatures (7, 10, 13 and 16° C, and a group called T-step, i.e. with temperature reduced successively from 16 to 13 and 10° C). After termination of the laboratory trial, the fish were moved to sea pens and reared at ambient conditions for 30 months before harvesting in June 2006. Observed growth gain from the 3 month laboratory trial was still persistent following the 30 months of sea-pen ongrowing. The T-step group displayed 15, 13, 1 and 10% superior mass gain respectively than the groups initially at 7, 10, 13 and 16° C at harvest in June 2006. Similarly, rearing under continuous light during the initial 3 month period during the early juvenile stage resulted in 1–9% larger size at harvesting compared to fish reared at simulated natural photoperiod. Gonado-somatic and hepato-somatic indices were similar in all groups. Contribution to the understanding of the mechanism behind size variation in adult fish can have wide range applications for Atlantic cod fisheries and aquaculture.     

Saline preferendum for the European sea bass, Dicentrarchus labrax, larvae and juveniles: effect of salinity on early development and sex determination

The sea bass, Dicentrarchus labrax, is an eurhyaline marine fish. Juveniles of this species are known to frequent estuaries and lagoons where salinity is lower than in the open sea. Sex determination occurs during this phase of fish life and has been shown labile and sensitive to environmental factors. In this work, the effect of rearing salinity on sex determination and early development of the sea bass was investigated. An excess of males (87%) was found in all groups and the salinity level [(natural sea water salinity, mean: 37‰) vs. (15‰)], when maintained constant, had no effect on the sex-ratio. The transfer from low to high salinity at 93 days post-fertilization (p.f.) increased the percentage of males (93%) suggesting that sexual differentiation in this species may be influenced by such an osmotic stress. Growth was improved by a 15‰ salinity at the beginning of larval rearing (14 days p.f.) and at the end of pre-growing (234-458 days p.f.), periods during which low temperatures were applied. Survival during larval rearing and nursery were also improved in the groups reared at low salinity and so was swimbladder inflation. These results show that sea bass juveniles have a low saline preferendum, a finding that corresponds to the conditions they actually encounter in the wild during their juvenile ecophase; sex determination is not directly modulated by the salinity level but seems to be subjected to complex environmental regulations.     

Growth of pike larvae: effects of prey, turbidity and food quality

We studied experimentally the effects of turbidity and prey composition on pike larval growth and hypothesized that pike larval growth varies with turbidity and food quality. We reared the first-feeding pike larvae (Esox lucius) in laboratory tanks with (1) clear or (2) turbid water provided with zooplankton rations from (3) an inner and (4) an outer archipelago site. The sites differ in physical features, salinity, eutrophication status, zooplankton community structure and density. Pike larvae showed the highest weight increase in clear water with zooplankton from the outer site and the poorest weight increase in turbid water with zooplankton as prey from the inner site. Our fatty acid analysis revealed that unsaturated fatty acid levels were highest in the outer site. The relative percentage of copepods was also higher in the outer site. This study supports the hypothesis that turbidity weakens the ability of pike larvae to capture certain prey. Further, zooplankton community composition matters in turbid water, but is not a primary factor in clear water.     

Hatch-period-dependent early growth and survival of Pacific herring Clupea pallasii in Miyako Bay, Japan

Considerable interannual variation in the abundance of larval and juvenile Pacific herring Clupea pallasii was detected in Miyako Bay, on the Pacific coast of northern Japan; abundances were high in 2001 and 2003 and low in 2000 and 2002. Hatch dates and growth rates for larval and juvenile survivors were estimated through otolith analysis. Water temperature and food availability were monitored on the spawning and nursery grounds in the inner part of the bay. The number of spawning females caught in nets set around the spawning ground was recorded during each spawning season (January to May) in 2000–2003. No correlation was found between the number of spawning females and the abundance of larvae and juveniles on the spawning and nursery grounds. The hatch dates of surviving larvae and juveniles were concentrated at the end of the spawning season in 2001 and in the middle of the season in 2003. The larvae experienced relatively high prey concentrations during the first-feeding period in 2001 but low concentrations in 2003. Survival of larvae during the first-feeding period may be a function of prey concentration as well as water temperature. In 2003, low water temperature would reduce starvation mortality during the first-feeding period. In contrast, unfavourable feeding conditions with higher temperatures during the first-feeding period seemed to result in low larval survival in 2000 and 2002. The 2001 larvae grew faster than those in 2003 because of the late hatch dates and the higher ambient temperatures that resulted. Temperature might be a major factor controlling growth rates of C. pallasii larvae in Miyako Bay.     

Early thermal history significantly affects the seasonal hyperplastic process occurring in the myotomal white muscle of <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> juveniles

The effect of early (embryonic and larval) thermal history on subsequent (juvenile) white muscle hyperplasia was studied in a teleost fish, the European sea bass (Dicentrarchus labrax L.). D. labrax, incubated and reared at constant temperatures of 13°C, 15°C or 20°C from the embryonic stage of half epiboly up to 18–19 mm in total length, were transferred to ambient seawater temperature and reared for the subsequent 14 months on commercial feed. The somatic growth of juveniles was linked to annual variations of ambient seawater temperature and inversely related to early rearing temperature, so that, after 14 months, the juveniles originally reared at low temperatures had compensated for the growth retardation experienced during early life. The white muscle growth process of juveniles was quantified after two periods of growth opportunity at ambient seawater temperature (100 and 400 days post-transfer) as well as, in order to follow total-length-dependent effects of early temperature and to discriminate total-length-independent effects of early temperature, on juveniles from the three batches sampled at six successive equivalent total lengths (31–33, 84–88, 141–145, 166–172, 196–206 and 211–220 mm). Our data demonstrate the existence of a seasonal recruitment of new white muscle fibres when seawater temperature increases and of a shrinkage of the largest white muscle fibres during the winter months. The seasonal recruitment of new white muscle fibres occurring in juveniles is linked to their early rearing temperature. Juveniles originating from low temperatures have a higher and longer capacity to recruit new white muscle fibres when seawater temperature increases, supporting their better somatic growth. This finding is discussed in relation to the early (embryonic and larval) myogenic processes of the three populations and is related to their sex ratio. This work was financed by the European Commission, FAIR Program no. PL96–1941 “Muscle Ontogeny in Sea bass and Trout”.     

The influence of food distribution upon the development of aggressive and competitive behaviour in juvenile chum salmon, Oncorhynchus keta

Groups of juvenile chum salmon were reared on food that was either dispersed throughout, or localized in one area of, the rearing tank. Groups receiving localized food displayed more aggression than those receiving dispersed food. This led to differences in growth, with fish reared on localized food having greater individual growth variability, i.e. growth depensation. However, after several months of rearing in these different feeding/social environments, fish reared on dispersed food were just as aggressive when first exposed to localized food as were fish reared on localized food. Furthermore, in competitive contests between fish of the two rearing histories, those reared on dispersed food were just as likely to become dominant as those reared on localized food. These results suggest that the behavioural development of aggressiveness is not amenable to alteration by manipulation of food distribution.     

Expression of the oligopeptide transporter, PepT1, in larval Atlantic cod (Gadus morhua)

The intestinal absorption of di- and tri-peptides generally occurs via the oligopeptide transporter, PepT1. This study evaluates the expression of PepT1 in larval Atlantic cod (Gadus morhua) during the three weeks following the onset of exogenous feeding. Larval Atlantic cod were fed either wild captured zooplankton or enriched rotifers. cDNA was prepared from whole cod larvae preceding first feeding and at 1000 each Tuesday and Thursday for the following three weeks. Spatial and temporal expression patterns of PepT1 mRNA were compared between fish consuming the two prey types using in situ hybridization and quantitative real-time PCR. Results indicated that PepT1 mRNA was expressed prior to the onset of exogenous feeding. In addition, PepT1 was expressed throughout the digestive system except the esophagus and sphincter regions. Expression slightly increased following first-feeding and continued to increase throughout the study for larvae feeding on both prey types. When comparing PepT1 expression in larvae larger than 0.15-mg dry mass with expression levels in larvae prior to feeding, no differences were detected for larvae fed rotifers, but the larvae fed zooplankton had significantly greater PepT1 expression at the larger size. In addition, PepT1 expression in the zooplankton fed larvae larger than 0.15-mg dry mass had significantly greater expression than rotifer fed larvae of a similar weight. Switching prey types did not affect PepT1 expression. These results indicate that Atlantic cod PepT1 expression was slightly different relative to dietary treatment during the three weeks following first-feeding. In addition, PepT1 may play an important role in the larval nutrition since it is widely expressed in the digestive tract.     

Reproductive Physiology of Fishes

Atlantic cod Gadus morhua larvae reached four‐fold (at low larval density) to 11 fold higher body mass (high larval density) at 50 days post hatch (dph) when fed zooplankton rather than enriched rotifers. A short period (22–36 dph) of dietary change affected larval growth positively if changed from enriched rotifers to natural zooplankton and negatively if prey type changed vice versa. Overall survival did not differ between the two larval groups at low larval density, but at high density the rotifer group had a higher overall survival (10·8% v. 8·9%). Long‐term growth was affected significantly by larval diet in favour of the zooplankton diet; juveniles reached a 23% higher mass in a 12 week growth period. No difference in growth performance was found between juveniles fed natural zooplankton during the larval period for 36, 22 or 14 days, but all these juveniles performed significantly better compared with the rotifer‐fed group. These findings suggest that optimal diet during a short period in the larval period can result in improved growth in both the larval and juvenile period. Improved rotifer quality may, therefore, hold a large potential for growth improvement in this species.     

Experimental studies on the larval development of the shrimpsCrangon crangon andC. allmanni

Larvae of the shrimpsCrangon crangon L. andC. allmanni Kinahan were reared in the laboratory from hatching through metamorphosis. Effects of rearing methods (larval density, application of streptomycin, food) and of salinity on larval development were tested only inC. crangon, influence of temperature was studied in both species. Best results were obtained when larvae were reared individually, with a mixture ofArtemia sp. and the rotiferBrachionus plicatilis as food. Streptomycin had partly negative effects and was thus not adopted for standard rearing techniques. All factors tested in this study influenced not only the rates of larval survival and moulting, but also morphogenesis. In both species, in particular inC. crangon, a high degree of variability in larval morphology and in developmental pathways was observed. Unsuitable conditions, e.g. crowding in mass culture, application of antibiotics, unsuitable food (rotifers, phytoplankton), extreme temperatures and salinities, tend to increase the number of larval instars and of morphological forms. The frequency of moulting is controlled mainly by temperature. Regression equations describing the relations between the durations of larval instars and temperature are given for bothCrangon species. The number of moults is a linear function of larval age and a power function of temperature. There is high variation in growth (measured as carapace length), moulting frequency, morphogenesis, and survival among hatches originating from different females. The interrelations between these different measures of larval development in shrimps and prawns are discussed.     

Environmental rearing conditions produce forebrain differences in wild Chinook salmon Oncorhynchus tshawytscha

Recent studies suggest that hatchery-reared fish can have smaller brain-to-body size ratios than wild fish. It is unclear, however, whether these differences are due to artificial selection or instead reflect differences in rearing environment during development. Here we explore how rearing conditions influence the development of two forebrain structures, the olfactory bulb and the telencephalon, in juvenile Chinook salmon (Oncorhynchus tshawytscha) spawned from wild-caught adults. First, we compared the sizes of the olfactory bulb and telencephalon between salmon reared in a wild stream vs. a conventional hatchery. We next compared the sizes of forebrain structures between fish reared in an enriched NATURES hatchery and fish reared in a conventional hatchery. All fish were size-matched and from the same genetic cohort. We found that olfactory bulb and telencephalon volumes relative to body size were significantly larger in wild fish compared to hatchery-reared fish. However, we found no differences between fish reared in enriched and conventional hatchery treatments. Our results suggest that significant differences in the volume of the olfactory bulb and telencephalon between hatchery and wild-reared fish can occur within a single generation.     

The environmental and genetic control of seasonal polyphenism in larval color and its adaptive significance in a swallowtail butterfly

Seasonal polyphenism, in which different forms of a species are produced at different times of the year, is a common form of phenotypic plasticity among insects. Here I show that the production of dark fifth-instar caterpillars of the eastern black swallowtail butterfly, Papilio polyxenes, is a seasonal polyphenism, with larvae reared on autumnal conditions being significantly darker than larvae reared on midsummer conditions. Both rearing photoperiod and temperature were found to have individual and synergistic effects on larval darkness. Genetic analysis of variation among full-sibling families reared on combinations of two different temperatures and photoperiods is consistent with the hypothesis that variation in darkness is heritable. In addition, the genetic correlation in larval darkness across midsummer and autumnal environments is not different from zero, suggesting that differential gene expression is responsible for the increase in larval darkness in the autumn. The relatively dark autumnal form was found to have a higher body temperature in sunlight than did the lighter midsummer form, and small differences in temperature were found to increase larval growth rate. These results suggest that this genetically based seasonal polyphenism in larval color has evolved in part to increase larval growth rates in the autumn.     

Observations on the reproductive and larval biology ofBlennius pavo (Pisces: Teleostei)

Social behaviour and spawning of adultBlennius pavo kept in the laboratory are described. Eggs are deposited in batches on the walls of artificial spawning places (PVC pipes). One male guards and tends the eggs of different females in one spawning place. Larval hatching occurs in groups according to oviposition. Minimum incubation temperature is around 14–15°C. Larval survival in 1-1 rearing jars is not related to larval total length but to density of larval stock. An experimental population of laboratory reared juvenile and adolescentB. pavo displays a male to female ratio of 1:1.4. Factors possibly influencing the sex ratio of this littoral fish are discussed in view of the situation in its natural environment.     

Occurrence of Larval and Early Juvenile Fishes in the Surf Zone Adjacent to two Intermittently Open Estuaries, South Africa

I monitored larval and early juvenile fishes in the surf zone adjacent to two warm temperate, intermittently open estuaries in South Africa. Mugilidae (59–67%) dominated fish assemblages in the surf zones adjacent to the Van Stadens and Kabeljous estuaries. Other dominant families included the Atherinidae, Sparidae and Soleidae. The most abundant species caught during the study were the catadromous mugilid Myxus capensis, in a postflexion or early juvenile stage of development, and the sparid Rhabdosargus holubi, in a postflexion stage of development. Species displaying a degree of dependence on estuaries during the early phase of their life cycle dominated (96–98%) surf zone catches. Most fish encountered were at the postflexion stage of larval development. Larval and early juvenile fishes were more abundant during the summer and autumn months with density peaking several-fold during natural estuary opening events, particularly in the surf zone adjacent to the Kabeljous Estuary. Decreases in salinity showed a significant relationship with increases in fish density during a March opening event in the surf adjacent to the Kabeljous Estuary where catches were concentrated along a current-driven estuarine plume. Catches adjacent to the Van Stadens Estuary also increased considerably during two smaller opening events in March and November although salinity played no statistically significant role in these increased catches. Results from the surf adjacent to the Van Stadens Estuary suggested that either very small amounts of estuarine water entering the surf zone can elicit an accumulation response by estuary-dependent larval and early juvenile fishes or that an additional characteristic of estuary/river water, other than salinity per se, is aiding the cueing process.     

The effect of initial larval stocking density on growth and survival in common barbel Barbus barbus (L.)

Aim of the study was to determine the effect of initial larval density on growth and survival of the common barbel Barbus barbus (L.) under controlled conditions. The experiment examined fish density from 20 to 200 ind. L^?1 during intensive rearing at 25°C. Rearing lasted 21 days whereby the average total fish length, weight and survival were recorded. During the entire period fish were fed live nauplii Artemia sp. The data provided the basis for calculating the specific growth rate (SGR), Fulton’s condition index (K), and analysis of the relationship between biomass and the stocking density. The documentation was also used to determine the level of ontogeny. The study data obtained indicated that initial larval density has no effect on survival (over 98% in each treatment), level of ontogeny, or on the rearing indexes. Fish achieved the juvenile stage during the second week of rearing (<23 mm total length). At the end of the experiment fish reached 26.50–27.78 mm TL. SGR ranged from 22.75 to 23.53 (% day^?1). No statistical differences were found among all treatments (P > 0.05). The findings of this study suggest that stocking density in common barbel larvae is not a factor limiting growth or the ontogenetic development rate during initial rearing. This creates considerable potential for improvement in stocking material production under controlled conditions and should have a positive effect on the economic effectiveness of production.     

Development of feeding structures in larval fish with different life histories: winter flounder and Atlantic cod

The size at which feeding structures developed and shifts in head proportions occurred, differed between Atlantic cod Gadus morhua and winter flounder Pseudopleuronectes americanus. The sequence and timing of the development of feeding structures may not be dependent on size, but may occur because they are necessary to meet specific requirements offish larvae feeding in the plankton. In early larval stages development of feeding structures was similar in number and type and was necessary for first-feeding in both species. In later stages, significant differences between species occurred in the timing of the development of feeding structures. In cod differentiation of new structures and changes in head proportions occurred at about two-thirds of the way through larval life, which coincided with an increase in growth. In flounder changes in feeding morphology did not occur during the symmetrical larval stage, but occurred only after metamorphosis to the asymmetrical demersal juvenile stage. Differences between cod and flounder in the size at which feeding structures develop may reflect life history adaptations expressed in the duration of the pelagic larval stage, as well as differences in juvenile habitat and feeding ecology.     

Ultrastructure of the mushroom body: digestion during metamorphosis of Utterbackia imbecillis (Bivalvia: Unionidae)

Abstract. Larvae of the freshwater mussel Utterbackia imbecillis metamorphose to juveniles either during their attachment to a host fish, or in vitro in a culture medium. This transformation includes degeneration of larval structures and development of the juvenile morphology. Early in metamorphosis the cells comprising the larval mantle enlarge and project into the mantle cavity, forming a structure referred to as the mushroom body. Its cells, which are ultrastructurally very similar to digestive cells of adult bivalves, are involved in pinocytosis or phagocytosis of the larval adductor muscle and of tissue from the host fish that is enclosed between the larval shells. Ingested material is passed from pinosomes to heterophagosomes which in turn fuse with heterolysosomes, where final degradation of ingested material occurs. Acid phosphatase activity was detected in heterophagosomes and heterolysosomes of all animals examined. In larvae that metamorphosed in vitro , the apical cytoplasm of the cells of the mushroom body, and the extracellular spaces among them, also exhibited acid phosphatase activity. Larvae reared on a host fish accumulated substantial deposits of lipids and glycogen within larval mantle cells during metamorphosis, whereas larvae reared in vitro did not. The larval mantle cells which constitute the mushroom body appear to be the primary sites of intracellular digestion of the larval adductor muscle and host tissue during metamorphosis.     

Allometric and ontogenetic larval development of common barbel during rearing under optimal conditions

The rearing of finfish larvae is a key element in their further culture. Improper breeding protocols may result in high mortality rates, body deformation and growth rate decreases in both the larval and fattening periods. These errors can be avoided by thorough exploration of various aspects of early larvae biology, at least in model fish species. In this study, anatomical and morphological developments were analysed using allometric growth patterns of common barbel, Barbus barbus, larvae reared under optimal controlled conditions. Larvae of common barbel, which is a model species for fish of the genus Barbus, were reared for 30 days at 25 °C in the recirculated aquaculture system (RAS). Four periods of the barbel larval development were identified: pre-flexion (0–5 days post hatching – DPH; total length – TL: 9.5 ± 0.3 to 12.3 ± 0.3 mm), flexion (6–11 DPH; TL 12.4 ± 0.3–15.4 ± 0.3 mm), post-flexion (12–21 DPH; TL 16.1 ± 0.5–21.2 ± 0.8 mm) and juvenile (from 22 DPH; TL from 21.4 ± 1.7 mm). The largest changes in barbel growth were observed during the first two periods of their life (pre-flexion and flexion), which resulted in the frequency of noted flexion points (64.3% flexion points) and was also associated with intensive morphometric growth, primarily the head and tail parts of the body. Despite a low degree of growth progress upon hatching (e.g. no eye pigment, no distinct liver or pancreas, no unobstructed alimentary tract), barbel larvae pass through the larval periods very quickly in comparison to other cyprinids and enter the juvenile period (22 days).     

Effects of induced variation in anuran larval development on postmetamorphic energy reserves and locomotion

Anuran larvae exhibit high levels of phenotypic plasticity in growth and developmental rates in response to variation in temperature and food availability. We tested the hypothesis that alteration of developmental pathways during the aquatic larval stage should affect the postmetamorphic performance of the Iberian painted frog (Discoglossus galganoi). We exposed tadpoles to different temperatures and food types (animal- vs. plant-based diets) to induce variation in the length of the larval period and body size at metamorphosis. In this species, larval period varied with temperature but was unaffected by diet composition. In contrast, size at metamorphosis was shaped by the interaction between food quality and temperature; tadpoles fed on an animal-based diet became bulkier metamorphs than those fed on plant-based food at high (22°C) but not at low (12°C) temperature. Body condition of newly metamorphosed frogs was unrelated to the temperature or food type experienced during the premetamorphic stage. Frogs maintained at high temperature during the larval period showed reduced jumping ability, especially when fed on the plant-based diet. However, when considering size-independent jumping ability, cold-reared individuals exhibited the lowest performance, and herbivores reared at 17°C the highest. Cold-reared (12°C) frogs accumulated larger amounts of energy reserves than individuals raised at 17°C or 22°C. This was still the case after correction for differences in body mass, thus indicating some size-independent effect of developmental temperature. Despite the higher lipid content of the carnivorous diet, the differences in energy reserves between herbivores and carnivores were relatively weak and associated with differences in body size. These results suggest that the consequences of environmental variation in the larval habitat can extend to the terrestrial phase and influence juvenile growth and survival.     

Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river

We reared juvenile Chinook salmon for two consecutive flood seasons within various habitats of the Cosumnes River and its floodplain to compare fish growth in river and floodplain habitats. Fish were placed in enclosures during times when wild salmon would naturally be rearing in floodplain habitats. We found significant differences in growth rates between salmon reared in floodplain and river enclosures. Salmon reared in seasonally inundated habitats with annual terrestrial vegetation experienced higher growth rates than those reared in a perennial pond on the floodplain. Growth of fish in the non-tidal river upstream of the floodplain varied with flow in the river. When flows were high, there was little growth and high mortality, but when the flows were low and clear, the fish grew rapidly. Fish displayed very poor growth in tidally influenced river habitat below the floodplain, a habitat type to which juveniles are commonly displaced during high flow events due to a lack of channel complexity in the main-stem river. Overall, ephemeral floodplain habitats supported higher growth rates for juvenile Chinook salmon than more permanent habitats in either the floodplain or river. Variable responses in both growth and mortality, however, indicate the importance of providing habitat complexity for juvenile salmon in floodplain reaches of streams, so fish can find optimal places for rearing under different flow conditions.     

Effects of ambient colour on colour preference and growth of juvenile rainbow trout Oncorhynchus mykiss (Walbaum)

Colour preference of individual juvenile rainbow trout Oncorhynchus mykiss was tested at 1 and 12° C, and also at 12° C after a 42 day growth experiment under white, blue, green, yellow or red ambient colour. All experiments were carried out under controlled laboratory conditions and the preference was assessed by the location of the fish in a preference tank with four chambers. Rainbow trout showed a preference for blue and green at 1° C and for green at 12° C. After the growth experiment the fish reared in blue tanks preferred blue and green but green was the most preferred colour for the fish reared in green, yellow and red tanks. Yellow and especially red chambers were avoided, irrespective of the ambient colour during the growth trial. The final mass of fish reared in the red aquaria was significantly smaller than that of the fish in green tanks. In addition, when the data of the preference tests were correlated with the data of the growth experiment using mean values of the four tested colours, a very good linear relationship was observed between the preference ( i.e. visit frequency in coloured compartments) and growth rate as well as food intake. When considering the results both from the preference and growth trials it is suggested that green is the best environmental colour for rearing juvenile rainbow trout while rearing in a red environment cannot be recommended.