Early Juvenile Growth Research Articles

Variable larval growth in a coral reef fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 206:213-226 (2000) - doi:10.3354/meps206213 Variable larval growth in a coral reef fish Steven P. Searcy*, Su Sponaugle** Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, New York 11794-5000, USA Present addresses: *Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695-8208, USA. E-mail: spsearcy@unity.ncsu.edu **Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida, Miami 33149-1098, USA ABSTRACT: Understanding the functional linkages between the pelagic and demersal stages of marine organisms is a central goal in ecology. To better understand events that occurred during the larval period as well as their initial influence on juvenile traits, we examined individual level variation in early life-history traits (larval and early juvenile otolith growth rates, size-at-age, and larval duration) of 3 seasonal cohorts of the common coral reef fish Thalassoma bifasciatum (Bloch) (Labridae). Juveniles were collected at regular intervals (every second day) for 2 wk following their first appearance on the nearshore reefs of Barbados, West Indies. Otolith analysis indicated that each cohort exhibited a broad range of larval traits. Individuals with shorter larval durations had faster otolith growth and settled at relatively smaller sizes (based on otolith length and standard length) than larvae with longer larval durations, which exhibited slower otolith growth rates. Despite the range in larval durations for T. bifasciatum, otolith growth records revealed no evidence for delay of metamorphosis. Instead, the range in larval durations is likely to be the result of a variable pelagic environment influencing growth rates. Because metamorphosis in this species is an energetically costly non-feeding (3 to 5 d) period, we propose that successful metamorphosis requires a minimum energy reserve. Slower growers may need to remain in the plankton longer (consequently attaining larger sizes) to obtain this minimum condition. Variability in early life-history traits also occurred among the seasonal cohorts. Despite differences in patterns of larval otolith growth, mean larval duration was similar for the 2 fall cohorts (57 and 55 d), but much shorter for the spring cohort (42 d). Such inter-cohort variability in early life-history traits suggests a variable pelagic environment. In contrast to the larval period, juvenile growth rates were much less variable within and among cohorts, reflecting a more constant physical and biological environment on the reef. KEY WORDS: Coral reef fish · Early life-history traits · Juvenile growth · Larval growth · Growth plasticity · Otolith · Pelagic larval duration · Condition at settlement · Thalassoma bifasciatum Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 206. Online publication date: November 03, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

Food Availability is not a Limiting Factor in the Growth of Three Australian Temperate Reef Fishes

An assumption often made but rarely tested is that post-recruitment stocks of temperate reef fishes are rarely resource limited, particularly for resources influencing growth. This has been particularly attributed to significant interranual variation in recruitment strength such that in most years stocks are not structured by intra-specific competition for resources. This assumption was tested for three temperate Australian species, the labrids Notolabrus fucicola and N. tetricus, and the monacanthid Penicipelta vittiger, by comparing growth rates from 4 to 5 randomly selected, isolated locations sharing similar habitats in south eastern Tasmania. If food resources were limiting, growth should have differed between locations depending on the ratio of population density to available food resources at each location. In comparisons of the length at age relationships between locations by ANOVA, no significant differences were detected, either in growth curve elevation or shape. These results indicate that growth is similar between locations, both spatially and temporally, and suggest growth is unlikely to be limited by density-dependent factors. Growth rates were also compared between two regions subject to differing environmental conditions. One region was influenced by river discharge waters, the other by oceanic waters. Growth differences were detected between the regions for N. fucicola and N. tetricus but not P. vittiger. The growth differences were related to either early juvenile growth rates or differing timing of recruitment between regions. For most species of temperate fishes, environmental conditions may influence growth to a greater extent than variations in food availability, presumably because local population sizes are usually below the level at which competition for food becomes important.

Positive effects of large concentration in culture on the development of the lecithotrophic larvae of Babylonia formosae (Sowerby) (Prosobranchia: Buccinidae)

The negative effects of large larval concentration on larval development have been reported for many marine planktotrophic invertebrates. Comparable data for the lecithotrophic species are, however, not available. The present study was therefore undertaken to determine the influence of varying larval concentrations on the developmental performance of Babylonia formosae (Sowerby). The larvae of B. formosae were cultured at four concentrations: 1, 2, 4 and 8 larvae ml−1. Over the 6-day experimental period, the cumulative percent settlement increased from 73, 83, 89 to 95%, and the mean settling time decreased from 3.88, 4.46, 3.62 to 3.21 days as the concentration increased from 1, 2, 4 to 8 larvae ml−1, respectively. What was found was a positive correlation between larval concentration and cumulative percent settlement (Y=74.35+2.80X; R2=0.61; p<0.01) as well as a negative correlation between larval concentration and mean settling time (Y=4.31−0.14X; R2=0.59; p<0.01). It was hypothesized that lecithotrophic larvae accelerate their developmental rate to shorten the suboptimal planktonic period and to minimize substrate competition with increased larval concentration. When juveniles were reared at 0.2 individuals ml−1 in one experiment, they all survived regardless of the concentration at which larvae were reared, and no significant difference was found in the cumulative increment of shell length on days 4, 8, 12 or 16. The mean growth rate was 39 μm d−1. In a second experiment, however, juvenile mortality was 37 to 47% when juveniles were reared at higher concentrations (1 to 8 juveniles ml−1). The juvenile growth rate also decreased from 29, 26, 23 to 18 μm d−1 as the concentration increased from 1, 2, 4 to 8 juveniles ml−1, respectively. The cumulative increment of shell length in different concentrations was significantly different on day 16 (P<0.05), and there was a negative correlation between juvenile concentration and cumulative increment of shell length (mm) (Y=0.469−0.024X; R2=0.12; P<0.01). Although juveniles clearly do better at low juvenile concentrations, the experiences of planktonic larval concentration may influence the rate of early juvenile growth was not indicated.

Costs of delayed metamorphosis: reduced growth and survival in early juveniles of an estuarine grapsid crab, Chasmagnathus granulata

When the megalopa stage of estuarine crab species becomes competent for settlement and metamorphosis, it responds to specific chemical and physical cues from the adult environment. Delayed metamorphosis in the absence of such cues is beneficial insofar as it increases the probability of finding a suitable habitat, and it may also enhance the genetic exchange between separate populations. However, this developmental and behavioural response may incur energetic costs reducing the fitness of later life-history stages. In a laboratory investigation, we studied postmetamorphic consequences of delayed metamorphosis for growth and survival in early juvenile instars (I through V) of an estuarine grapsid crab, Chasmagnathus granulata (Dana, 1851). In competent megalopa larvae of this species, metamorphosis is induced by chemical cues from muddy substrates and conspecific adults (control treatment). After delayed metamorphosis in the absence of these cues (experimental treatment), survival and body size were significantly reduced in the first crab stage, and the duration of development to the second juvenile instar was significantly longer. Survival, moult-cycle duration, and percentage growth increments were not significantly affected in later juvenile instars. However, as a consequence of the initial reduction in development and growth, the crabs from the experimental treatment remained consistently smaller and moulted later to successive instars than in the control group. Our results indicate that delayed metamorphosis is associated with a reduced postmetamorphic fitness in an estuarine crab species.

Feeding and growth of early juvenile Japanese sardines in the Pacific waters off central Japan

Larval and early juvenile growth was backcalculated for individual Japanese sardines Sardinops melanostictus using the biological intercept method based on the allometric relationship between otolith radii and fish lengths. Sardines grew at 0·81 mm day−1 during the larval stage. In the early juvenile stage, they grew from 32·3 to 45·4 mm fork length (L) over a 20-day period (0·64mm day−1). Using the observed relationship between L and wet body weight (W), W = 0·00942 L2.99, W of the sardine juveniles was calculated to increase from 306 to 832 mg during the 20-day period. The carbon (C) requirement to achieve this growth in weight was estimated to increase from 5·7 to 9·6 mg day−1. Stomach contents of the sardines were composed mostly of copepods (73%) and larvaceans (25%). Wet stomach content weight (Ws) was expressed by a power function of the W, Ws=0·731 W0·658. Carbon and nitrogen constituted 41·7 ± 1·5 and 10·0 ± 0·4% of the dry Ws, respectively. Stomach C content increased from 2·0 to 3·9 mg during the 20-day period. Three to four cycles of the daily turnover of stomach contents during the 16 h of daytime, corresponding to a gastric evacuation rate of 0·2–0·3 h−1 under continuous feeding, met the C requirement to achieve the backcalculated growth in early juvenile sardines. The Kuroshio frontal waters seem to provide Japanese sardine juveniles with favourable growth conditions.

Feeding and growth of early juvenile Japanese sardines in the Pacific waters off central Japan

Larval and early juvenile growth was backcalculated for individual Japanese sardines Sardinops melanostictus using the biological intercept method based on the allometric relationship between otolith radii and fish lengths. Sardines grew at 0·81 mm day−1 during the larval stage. In the early juvenile stage, they grew from 32·3 to 45·4 mm fork length (L) over a 20‐day period (0·64mm day−1). Using the observed relationship between L and wet body weight (W), W = 0·00942 L2.99, W of the sardine juveniles was calculated to increase from 306 to 832 mg during the 20‐day period. The carbon (C) requirement to achieve this growth in weight was estimated to increase from 5·7 to 9·6 mg day−1. Stomach contents of the sardines were composed mostly of copepods (73%) and larvaceans (25%). Wet stomach content weight (Ws) was expressed by a power function of the W, Ws=0·731 W0·658. Carbon and nitrogen constituted 41·7 ± 1·5 and 10·0 ± 0·4% of the dry Ws, respectively. Stomach C content increased from 2·0 to 3·9 mg during the 20‐day period. Three to four cycles of the daily turnover of stomach contents during the 16 h of daytime, corresponding to a gastric evacuation rate of 0·2–0·3 h−1 under continuous feeding, met the C requirement to achieve the backcalculated growth in early juvenile sardines. The Kuroshio frontal waters seem to provide Japanese sardine juveniles with favourable growth conditions.

Early life history of Hemigrapsus sanguineus, a non-indigenous crab in the Middle Atlantic Bight (USA)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 170:231-238 (1998) - doi:10.3354/meps170231 Early life history of Hemigrapsus sanguineus, a non-indigenous crab in the Middle Atlantic Bight (USA) C. E. Epifanio*, A. I. Dittel, S. Park, S. Schwalm, A. Fouts Graduate College of Marine Studies, University of Delaware, Lewes, Delaware 19958, USA *E-mail: epi@udel.edu ABSTRACT: The Japanese shore crab Hemigrapsus sanguineus (de Haan) was recently introduced to the northeast coast of the USA. The crab has established intertidal populations extending throughout the Middle Atlantic Bight. This study defines early-life-history characteristics that are germane to range extension in this species. Results of the investigation showed that the spawning season of H. sanguineus continues for at least 4 mo in the southern Middle Atlantic Bight. This is considerably longer than the spawning seasons of co-occurring native crabs. Eggs hatch about 14 d after extrusion, and females have the potential to produce several broods each year. Zoeal larvae are tolerant of a wide range of temperature/salinity combinations, and mean duration of zoeal development ranges from approximately 16 d at 25°C to 55 d at 15°C. At 25°C zoeae are capable of development to the megalopa stage at salinities as low as 15o/oo. At lower temperatures the zoeae require salinities above 20o/oo. The megalopa stage appears to have more stringent temperature/salinity requirements, which may restrict H. sanguineus to rocky shores of the coastal ocean and the adjacent high-salinity regions of the estuary. Under these conditions megalopae molt to the first juvenile stage in approximately 25 d post hatching. Newly metamorphosed crabs reach the fifth juvenile instar in 35 d. Dry-weight growth of zoeal larvae and early stage juveniles is exponential at respective rates of 23 and 8% of body weight per day. KEY WORDS: Non-indigenous · Exotic · Crab · Larvae · Juvenile · Growth Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 170. Publication date: September 03, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

The relationship between prey selectivity and growth and survival in a larval fish

We examined prey preference, growth, and survival of small larval (8-10 mm total length (TL)), large larval (11-17 mm TL), and early juvenile (&gt;18 mm TL) walleye (Stizostedion vitreum) in laboratory aquaria and field mesocosms using multiple prey assemblages that included cladoceran, copepod, and rotifer prey of varied sizes. Both prey taxa and size affected prey preference during the larval period. All sizes of walleye avoided rotifer and nauplii prey. Small and large larvae selected for intermediate-sized (0.4-0.9 mm) cladoceran prey and selected against large prey (&gt;0.9 mm) of both taxa. Although neither capture efficiency nor handling time differed between prey taxa, larvae oriented more frequently towards cladoceran prey suggesting that they were more visible than copepods to these small fish. Larval walleye that were fed exclusively cladoceran prey survived better than fish that were fed other prey. Early juveniles selected primarily on the basis of prey size, choosing large copepods and cladocerans. Prey taxa did not affect early juvenile growth or survival. Prey taxa and prey size interacted with predator size to influence selectivity and its effect on growth and survival. Consequently, these factors must be considered in combination when examining the importance of foraging decisions in young fish.

Early juvenile growth of the abalone Haliotis australis in culture

Experimentally cultured juvenile Haliotis australis were fed different diets and their growth was measured. For juveniles between 3 and 6 mm in length the best growth was achieved on diatoms but macroalgal and artificial diets were also suitable for sustaining growth. The size at which the diet should be changed from microalgae to macroalgae was determined as 7 mm. Two batches of juveniles grown in a V-shaped tank rearing system averaged 15.9 ± 0.53 and 17.5 ± 0.69 mm in length after 13 and 12 months respectively. Methods to enhance the early juvenile growth are discussed.

Growth and elemental composition (C, N, H) in larvae and early juveniles of a South American salt marsh crab, Chasmagnathus granulata (Decapoda: Grapsidae)

The semiterrestrial grapsid crab Chasmagnathus granulataDana is one of the most predominant inhabitants of brackish salt marsh ecosystems in South America. Its early postembryonic stages were reared in the laboratory from hatching of the first larval stage through the first juvenile crab instar, and changes in the quantity and elemental composition of biomass (measured as dry weight, W; carbon, C; nitrogen, N; hydrogen, H) were investigated in short intervals of time (every 1 or 2 d). In a series of successive developmental stages, the accumulation of biomass per individual can be described as an exponential function of the number of moults. In contrast, the pattern of growth within individual moulting cycles is described with best fit of observed and predicted data as a quadratic function of development time elapsed since last ecdysis. Weight-specific instantaneous growth rates show decreasing trends within the moulting cycle. Cumulative biomass increments during larval development of C. granulata are among the highest on record for brachyuran crabs. The quantities and patterns of larval growth are in this species similar as in most marine brachyuran crabs, for which data are available, but different from those in some other semiterrestrial grapsid crab species, which live in similar brackish water habitats as C. granulata. Hence, the early postembryonic stages of C. granulatado not show special bioenergetic adaptations to the non-marine conditions, which prevail in the adult habitat of this species. This reflects a strategy of larval export to the sea, i.e. a reproductive dependence of this species on the marine environment.

Physiological and biochemical changes during lecithotrophic larval development and early juvenile growth in the northern stone crab, Lithodes maja (Decapoda: Anomura)

Larvae of the northern stone crab, Lithodes maja L., were reared in the laboratory from hatching to the second crab stage. complete larval development (at constant 9°C) lasted about 7 wk, invariably consisting of three pelagic zoeal stages and a semibenthic Megalopa; only two zoeal stages have been described in the literature. All larval stages are lecithotrophic. First feeding was consistently observed only after metamorphosis, in the first juvenile crab stage. In short intervals (every 1 to 5 d), developmental changes in biomass, B (expressed as: dry weight, W; carbon, C; nitrogen, N; hydrogen, H) and oxygen consumption (respiration, R) were measured in larvae and early juveniles; additionally, protein and carbohydrates were measured, but only in the zoeal stages and early Megalopa. Unusually high C contents (varying between 56 and 61% of W in eggs and freshly hatched Zoea I larvae from 12 different females) and high C:N weight ratios (8 to 11) indicate enhanced initial lipid stores, which are utilized as the major metabolic substrate during both embryonic and lecithotrophic larval development. Predominant degradation of lipids is shown indirectly; the C:N ratio decreased significantly, from 10 (at hatching) to 6 (at metamorphosis), while larval protein decreased only little, from ca. 55% of W (at hatching) to 48% (in the Megalopa). From hatching to metamorphosis, about 27% of the initially present W, 48% of C, 18% of N, and 52% of H were lost. This decrease in larval biomass can be described as an exponential function of development time. The major part of these losses were associated with metabolic energy requirements, while exuvial losses were comparably small. In each of the zoeal stages, only about 1 to 2% of late premoult (LPM) B was shed with the exuvia. The Megalopa, which produces a much thicker, calcified exoskeleton, lost 20% of LPM W, but only 5 to 8% of organic constituents (C, N, H). Much higher exuvial losses were measured in the Crab I stage (51% in W, 21% in C, 5% in N, and 7% in H). Maximum respiration was found in the actively swimming zoeal stages, a minimum in the predominantly benthic, mostly inactive Megalopa. The Crab I stage exhibits also a sluggish behaviour and low R, in spite of beginning food uptake and growth. Immediately after metamorphosis, the juvenile crab gained rapidly in W, in particular in its C fraction. A transitorily steep increase in the C:N ratio indicates a replenishment of partially depleted lipid stores, but also a rapid initial increase of inorganic C in the heavily calcified exoskeleton. Instantaneous rates of growth, assimilation, and net growth efficiency (K 2) were high during the initial (postmoult) phase in the first juvenile crab stage (C-specific growth rate: 6% d-1; K 2:70%), but decreased towards zero values during laterstages of the moulting cycle; metabolism remained practically constant during the Crab I stage. Entirely lecithotrophic larval development from hatching to metamorphosis in L. maja is considered an adaptation to seasonally short and limited planktonic food production in subarctic regions of the northern Atlantic.

Influence of Temperature, Salinity, pH and Light on Molting and Growth in the Indian White Prawn Penaeus indicus (Crustacea: Decapoda: Penaeidae) under Laboratory Conditions

The effects of temperature (26, 31, 32.5 and 35°C), salinity (5, 15, 25, 35 and 45 ppt), pH (7±0.2, 8±0.2 and 9±0.2) and light (24hL:00hD, t2hL:12hD and 24hD:00hL) on the molt cycle and growth of early juveniles of Indian white prawn Penaeus indicus were investigated independently under laboratory conditions. Temperature, salinity and pH significantly (P&lt;0.01) influenced the molting and growth of the prawn. The influence by photoperiod was not significant (P&gt;0.05). The optimal levels of temperature, salinity and pH, which gave the fast molt with highest growth increment in P. indicus were 31 °C, 15 ppt and pH 8±0.2, respectively. Outside the optimum level, more molting did not produce more growth. Extreme levels of temperature, salinity and pH affected feed intake and normal molting resulting in poor tissue growth.

Changes in the physiological performance and energy metabolism of an estuarine mysid (Mysidopsis bahia) exposed in the laboratory through a complete life cycle to the defoliant DEF

Measures of physiological performance and energy metabolism were made on an estuarine mysid ( Mysidopsis bahia) exposed throughout a life cycle to the defoliant DEF. Continuous exposure to DEF concentrations ≥ 0.246 μg/l reduced survival through release of the first brood. Young production by individual females was completely arrested in DEF concentrations ≥ 0.606 μg/l. Life-cycle exposure to concentrations ≥ 0.085 μg DEF/l reduced young production by the population. An interaction between mysid age and DEF exposure concentration modified growth rates and energy metabolism. Growth of early juveniles was not altered by DEF exposure. However, concentrations ≥ 0.140 μg/l and ≥ 0,085 μg/l retarded growth rates in older juveniles and young adults, respectively. Exposure to these same DEF concentrations stimulated respiration rates of most juvenile stages and young adults. Following 5-days exposure to DEF concentrations ≥ 0.085 μg/l, mysids excreted less ammonia. O:N ratios of unexposed mysids became lower as juveniles matured, while DEF exposure resulted in higher O:N ratios. Higher O:N ratios during maturation of DEF-exposed mysids suggests greater reliance on energy-rich lipid substrates to support elevated metabolic demands, leaving reduced lipid for reproductive preparations.

Effects of sediment-bound endosulfan on survival, reproduction and larval settlement of meiobenthic polychaetes and copepods

Endosulfan-contaminated muddy sediments were collected from a tidal creek bottom after rain runoff from an agricultural watershed and tested for their effects on larval settlement/growth, survival and reproduction of cultured meiobenthic polychaetes and copepods. Endosulfan (ES) strongly inhibited larval colonization and early juvenile growth of the cosmopolitan, euryhaline polychaete Streblospio benedicti. In laboratory microcosms, ES concentrations as low as 50 μg·kg−1 sediment significantly reduced the number of larval colonists by >50% relative to ES-free control sediments. Higher concentrations closer to actual field levels suppressed Streblospio benedicti colonization completely. Early growth of newly metamorphosed juveniles was depressed 36 and 40% relative to controls at ES concentrations of 50 and 100 μg·kg−1, respectively. In contrast, when the common benthic harpacticoid copepod Pseudobradya pulchella was chronically exposed to sediment ES as high as 200 μg·kg−1, survival and egg production were unaffected despite many examples of high ES toxicity to other crustaceans. Of more than 1,600 Pseudobradya pulchella tested, more than 95% survived ES concentrations of at least 200 μg·kg−1, and over 98% of 1,200 females produced normal clutches of eggs. Similarly, survival of another common benthic copepod, Nannopus palustris, was not significantly affected below a threshold concentration of 200 μg·kg−1 ES. At 200 μg·kg−1, however, Nannopus palustris' survival was significantly reduced relative to control and 50-μg·kg−1 ES treatments.

The utility of artificial collectors as a technique to study benthic settlement and early juvenile growth of the rock crab, Cancer irroratus

Concurrent studies of planktonic larval density and benthic recruitment of Cancer irroratus were performed in Kochibouguac Bay, New Brunswick, from late May to mid-September 1981. Three artificial collector types were used; mop, box and Witham. All collector types were shown to sample settling C. irroratus. Although Homarus americanus is also abundant in this region, no settling stages or young juveniles were observed in the collectors. The most efficient collector appears to be the mop type, which should be tethered off the bottom to avoid excessive clogging on mud bottoms. The usefulness of these collectors in the study of growth of these otherwise inaccessible stages was demonstrated using modal analysis of size-frequency histograms. In addition, the presence of 26 exuviae (2.5–58 mm carapace width) showed that juveniles of all sizes molt in these collectors. The larval density data revealed a clear sequence of events, comprising the appearance of the first zoea larvae in early summer, the presence of a large megalopa peak in mid-July, followed immediately by the appearance of new recruits (⩾ first crab stage) in the collectors. The use of such artificial collectors constitutes a promising technique in the study of benthic recruitment and early growth of C. irroratus.

Facultative planktotrophy in the tropical echinoid Clypeaster rosaceus (Linnaeus) and a comparison with obligate planktotrophy in Clypeaster subdepressus (Gray) (Clypeasteroida: Echinoidea)

Larval development to metamorphosis and early juvenile growth and survivorship were examined in Clypeaster subdepressus (Gray) and C. rosaceus (Linnaeus). C. subdepressus has an obligatorily planktotrophic larva that metamorphoses after 16 to 28 days at 27°C. The larva of C. rosaceus can, but need not feed prior to metamorphosis, which occurs after 5 to 7 days at 27°C. Feeding by larvae of C. rosaceus does not change the time to metamorphosis but does increase size at metamorphosis, early juvenile growth and may increase juvenile survivorship relative to unfed larvae. Size at metamorphosis increases in larvae of C. rosaceus that feed for several days after they are competent to metamorphose, but there may be a limit to this increase because the condition of the rudiment degenerates after a period of time. The development of C. rosaceus may represent a transition between planktotrophy and lecithotrophy. This intermediate state has advantages for the juvenile stage that are not included in the trade of fecundity against risk to offspring usually considered in life history discussions of developmental mode of marine invertebrates.

Biotechnology in marine aquaculture

Intensification of production, modernization of technique, and improvement of cultivars are needed to increase the economic efficiency of marine aquaculture industries. To help achieve such improvements, modern methods of biochemical and genetic engineering can be adapted to control biological processes which intrinsically limit the efficiency and yield of production. Such applications now have been developed for improved production of molluscs. Critical life-cycle stages of several species of abalones and other commercially valuable molluscs which thus far have proved amenable to improved control by these means include reproduction, larval settlement, metamorphosis, and acceleration of early growth. Analysis of the physiological and molecular mechanisms which control reproduction in molluscs reveals a prostaglandin-dependent regulation of spawning in abalones and certain other species. Spawning of gravid adults can be induced by the addition of prostaglandins to the surrounding seawater, or, more reliably and inexpensively, by activation of the endogenous enzymatic synthesis of prostaglandin-related spawning triggers in response to added hydrogen peroxide. Peroxide activation of the prostaglandin-dependent spawning reaction has been found widely useful for obtaining synchronous and copious release of fully competent gametes in a large number of species of abalones, oysters, scallops, mussels, clams, and other valuable molluscs; a number of these species had not been successfully spawned by other methods. Settlement and metamorphosis of many molluscan species can be brought under similar biochemical control. Most efficiently and inexpensively, the natural biochemical requirement for induction of these critical developmental processes can be met by providing competent larvae with unique amino acid constituents associated with the naturally required inducing molecules. Thus, γ-aminoburyric acid (GABA) can be used simply, safely and inexpensively to induce complete and rapid larval settlement and metamorphosis — with minimal mortality — in many commercially important abalone species. This and similar neurotransmitter-related, amino-acid-derived compounds are proving comparably effective for the reliable induction of settlement and metamorphosis in a number of other valuable molluscan species. Recent analyses of the requirements for rapid early juvenile growth in abalones reveals a mechanism of growth-control which is susceptible to exogenous hormonal acceleration. Genetic cloning and amplification of recombinant-DNA templates for the efficient production of essential growth-regulating hormones, and substances required for enhanced nutritional efficiency and resistance of cultivars, are now in progress. Genetic engineering for the direct improvement of cultivated species soon will be within reach.

Biochemical and genetic engineering for improved production of abalones and other valuable molluscs

Intensification of production, modernization of technique, and improvement of cultivars are needed to increase the economic efficiency of molluscan cultivation industries in the United States and certain other countries. To help achieve such improvements, modern methods of biochemical and genetic engineering can be adapted to control biological processes which intrinsically limit the efficiency and yield of molluscan production. Critical life-cycle stages of several species of abalones and other commercially valuable molluscs which thus far have proved amenable to improved control by these means include reproduction, larval settlement, metamorphosis, and acceleration of early growth. Analysis of the physiological and molecular mechanisms that control reproduction in molluscs reveals a prostaglandin-dependent regulation of spawning in abalones and certain other species. Spawning of gravid adults can be induced by the addition of prostaglandins to the surrounding seawater, or, more reliably and inexpensively, by activation of the endogenous enzymatic synthesis of prostaglandin-related spawning triggers in response to added hydrogen peroxide. Peroxide activation of the prostaglandin-dependent spawning reaction has been found widely useful for obtaining synchronous and copious release of fully competent gametes in a large number of species of abalones, oysters, scallops, mussels, clams, and other valuable molluses; a number of these species had not been successfully spawned by other methods. Settlement and metamorphosis of many species can be brought under similar biochemical control. The efficient induction of settlement and metamorphosis of the larvae of many Haliotis (abalone) species normally requires contact with any of several crustose red algae usually associated with natural recruiting substrates. This requirement can be met by providing competent larvae with the essential algae or with specific proteins purified from these algae, although production of these inducers is both time consuming and costly. Most conveniently and inexpensively, this natural requirement can be met by providing the larvae with certain unique amino acid constituents normally associated with the inducing proteins. Thus, γ-aminobutyric acid (GABA) can be used simply, safely, and inexpensively to induce complete and rapid larval settlement and metamorphosis — with minimal mortality — in many commercially important abalone species. This and similar neurotransmitter-related, amino acid-derived compounds are proving comparably effective for the reliable induction of settlement and metamorphosis in a number of other valuable molluscan species. Recent analyses of the requirements for rapid early juvenile growth in abalones reveals a mechanism of growth control which is susceptible to exogenous hormonal acceleration. Present experiments aimed at genetic cloning and amplification of recombinant-DNA templates for the essential growth-regulating hormones, progress in the establishment of useful molluscan gene banks, and potential uses of this technology for molluscan aquaculture are described.

Larval and Early Juvenile Development of the Frillfin Goby, Bathygobius soporator (Perciformes: Gobiidae)

Larval and early juvenile development of laboratory-reared frillfin gobies, Bathygobius soporator (Cuvier and Valenciennes, 1837), is described and figured. One-day-old preserved specimens averaged 2.0 mm SL, had 11-12 preanal myomeres, and 25-26 total myomeres. Caudal fin rays appeared at 3.1 mm SL (10 days), followed by soft dorsal and anal fin rays at 3.4 mm SL (11 days). Dominant larval pigmentation consisted of dense rows of stellate melanophores along the dorsal and anal midlines and later along the lateral midline. The change to juvenile pigmentation and a benthic habit occurred at 4.7-5.4 mm SL (26-31 days). Early juvenile growth was characterized by migration of the eyes to the adult position, rounding of the caudal fin margin, beginning of scale formation, and separation of the upper pectoral fin rays.

Laboratory growth of early juveniles of the western rock lobster Panulirus longipes cygnus

Growth in the laboratory of early juvenile Panulirus longipes cygnus George from the last larval (puerulus) stage to approximately 3 years of age is described. Specimens were held either in isolation or in groups of 3 or 5 rock lobsters per tank, at constant temperatures of 20° or 23°C (both ± 0.5 C°) or at the temperatures of the incoming seawater, which ranged annually between 14.9° and 25.9°C. Metamorphosis from the planktonic puerulus to the settled juvenile existence involved a reduction in size and usually took about two moults to complete. By this time the sexes could be distinguished. Growth in aquaria from the 2nd moult after puerulus until the juveniles were approximately 3 years of age was adequately described by exponential (von Bertalanffy) functions, with the growth curves gradually tapering off after the rock lobsters had reached 40 to 42 mm carapace length. Young juveniles were not gregarious until 20 to 25 mm carapace length (approximately 1.5 years old), however, growth rates were not depressed in individuals held in isolation up to approximately 3 years of age. Temperature markedly affected growth; the fastest observed growth up to 450 days was at 23°C. Variations in temperature resulted in decreased growth rates in “winter” and the reverse in “summer” in individuals at ambient temperatures. There was an increase in the moult increment at successive moults corresponding to increased carapace length, but increased growth rates were achieved through shortening the intermoult duration. The period of development from the puerulus stage until approximately 1.5 years of age is a distinct phase of development both of behaviour and growth.