Myotome Height Research Articles

Effects of temperature and subspecies during critical early life history stages of largemouth bass (Micropterus salmoides)

Largemouth bass (LMB), Micropterus salmoides, is the most popular sportfish in the United States, with an expanding global food market. Farmers traditionally raise LMB in earthen ponds that are often plagued with high mortality during the early life history stages. Replacing initial pond stages with intensive indoor culture would streamline production and minimize losses. Our objectives were to (i) identify an optimal thermal regimen for rearing LMB in an indoor recirculation aquaculture system (RAS), (ii) assess the performance of Florida vs. Northern LMB for RAS culture, and (iii) elucidate thermally induced phenotypic changes and inter-linked expression of targeted genes involved in early development. Using RAS, Florida and Northern LMB were raised at 21 °C, 24 °C, and 27 °C. Fish were randomly sampled at 2 to 28 days post-hatch (dph) for total length (TL), body area (BA), myotome height (MH), jaw length (JL), eye diameter (ED), oil droplet area (ODA), and yolk area (YA). Condition index, yolk utilization efficiency (YUE), and yolk utilization rate (YUR) were calculated. Wet weight and survival were taken at 29 dph with expression of targeted genes [growth hormone (gh), insulin-like growth factor 1 (igf1), heat shock protein 70 (hsp70)] determined at 8 and 28 dph. There was a temperature effect on all morphometric traits, where both subspecies increased in size over the temperature gradient, with the largest morphometric traits (TL, BA, MH, JL, ED) detected at 27 °C. Larvae had smaller remaining ODA and YA reserves as temperatures increased. Larvae reared at 27 °C utilized their yolk at faster rates and were most efficient at converting yolk reserves to body size. Northern LMB had higher YUE than Florida LMB and were typically larger and heavier at 29 dph. LMB reared at 21 °C had higher survival than those at 24 or 27 °C, while Northern LMB had higher survival than Florida LMB. For Florida LMB, no differences in gh and igf1 were detected across temperatures at 8 dph. However, at 28 dph, these genes were upregulated at 27 °C, while expression of hsp70 was downregulated at 24 and 27 °C. Northern LMB showed similar expression patterns, with no significant differences detected. In conclusion, the present study suggests that 1) rearing LMB at 27 °C may improve growth performance during early ontogeny, and 2) Northern LMB may be selected for faster growth when reared in an indoor RAS.

Effects of first feeding regime on growth performance, survival rate and development of digestive system in pikeperch (Sander lucioperca) larvae

This study evaluated the effects of first feeding regime on growth performance, survival rate, and development of digestive organs (intestine, liver and pancreas) in pikeperch (Sander lucioperca) larvae. The fish larvae at 5 days post-hatch (DPH), were initially fed with rotifers (Brachionus plicatilis) for 3 days and from 8 to 17 DPH were fed with rotifers/Artemia for different time periods as follows: (A) only rotifers; (B) 8–13 DPH rotifers/14–17 DPH Artemia; (C) 8–10 DPH rotifers/ 11–17 DPH Artemia; (D) only Artemia; (E) a combination of rotifers and Artemia. Growth performance, survival rate and histological features of intestine, liver and pancreas were assessed at 11, 14 and 17 DPH to examine the effects of feeding regime. The groups fed rotifers for initial 3 days followed by feeding on Artemia (group D) (53 ± 5.43%) and combination of rotifers and Artemia (group E) (68 ± 5.51%), respectively, for the following 9 days showed significantly (P < .05) higher survival rates than the other groups (36–50%). The group fed merely on rotifers (groups A) exhibited significantly lower specific growth rate (SGR) than the other groups, and the highest SGR was found in the group fed with combination of rotifers and Artemia after 3 day rotifer feeding. Moreover, the highest total length (8.57 ± 0.57 mm), myotome height (0.75 ± 0.09 mm) and eye diameter (0.58 ± 0.05 mm) were obtained by combined feeding of rotifers and Artemia after 3 day of initial rotifer feeding. Significant differences among groups were found in morphometric parameters in the anterior intestine and liver. The results of histological examination of the liver, intestine and pancreas did not show any obvious pathological changes in all groups. In conclusion, feeding with rotifers from 5 to 8 DPH and afterwards with Artemia could be suggested as an economical feeding regime for first feeding of pikeperch larvae as comparable survival and growth to co-feeding with rotifers and Artemia were achieved.

Optimized application of rotifers Brachionus plicatilis for rearing pikeperch Sander lucioperca L. larvae

This study aimed to optimize the use of euryhaline rotifer Brachionus plicatilis for rearing larval pikeperch Sander lucioperca L. We assessed motility of rotifers under salinities of 0‰, 2‰, 4‰, 8‰, and 16‰ over a 6-h period. Rotifers stocked into freshwater were completely immotile within 2 h. The motility of rotifers after 6 h was 10 ± 2.27% at 2‰, 35 ± 5.58% at 4‰, 79 ± 30.35% at 8‰, and 92 ± 1.98% at 16‰. A second trial quantified the effect of the target salinity levels on pikeperch gut fullness over the course of 11 h. The gut fullness of larvae fed with rotifers was significantly lower at 8‰ salinity than in other tested groups. Salinity of 16‰ resulted in 100% mortality. Survival and growth of pikeperch larvae from 4 to 11 days post-hatching (DPH) was analyzed at low (2‰ and 4‰) and medium (8‰) salinity. Differences in larval performance under tested salinities were found in survival (S), total length, SGR, eye diameter, myotome height, and gut fullness. The highest mean survival (S) and specific growth rate (SGR) were obtained at 2‰ (S = 64%; SGR = 10 ± 5.4% day−1) and 4‰ (S = 65%; SGR = 8.23 ± 3.4% day−1) salinity and significantly differed from 8‰ (S = 36%; SGR = 5 ± 2.3% day−1) and control (S = 34%; SGR = 7 ± 3% day−1) at 11 DPH. At the conclusion of the trial (11 DPH), larvae of all exposures and control presented normal histology with no signs of pathology. Morphometric analyses revealed significant differences in brush border and fold height of anterior intestine among treatment groups. Larvae at 2‰ salinity showed significantly higher intestinal fold height (31.2 ± 5.40 μm) compared to those at 4‰ (26.5 ± 6.11 μm), 8‰ (26.3 ± 4.52 μm), and control (22.8 ± 5.13 μm) (p ˂ 0.05). Larvae at 4‰ salinity had significantly higher brush border height (2.50 ± 0.73 μm) compared to those at 2‰ (2.27 ± 0.63 μm) and 8‰ (1.87 ± 0.44 μm) salinity and control (1.66 ± 0.56 μm) (p < 0.05). The results showed 2‰ and 4‰ salinity supported higher numbers of motile B. plicatilis and higher larval survival and growth rate to 11 DPH.

Quantitative characteristics of Atlantic halibut (Hippoglossus hippoglossus L.) egg quality throughout the reproductive season

Assessment of egg quality is an important aspect in finfish hatchery management, but guidelines for such assessment are scarce, especially for marine fish production. In the present work, potential indicators of egg and larval quality were measured in 39 batches of eggs of Atlantic halibut (Hippoglossus hippoglossus L.) throughout the reproductive season. The paternal influence on offspring was minimized by using the same cryopreserved semen for all fertilizations; consequently, maternal effects were emphasized. The progression of the spawning season and ovarian fluid parameters, including pH, electrical conductivity (EC), osmolality, and the amount of fluid were registered. The behavior of the broodfish at egg collection was registered and the eggs were analyzed for cortisol content. Fertilization and hatching rates as well as larvae survival were calculated, and larval standard length and myotome height were measured. Furthermore, the occurrence of major types of larval deformities was registered. The myotome height was significantly (P < 0.05) affected by the spawning season progress. Cortisol content in the eggs was decreasing with the progressing spawning season and correlated positively with the occurrence of yolk-sac edema. The ovarian fluid pH and EC were significantly related to fertilization and hatching rates. High fertilization and hatching success was associated with pH greater than 7.9 and EC less than 2.5 mS/cm. Low fertilization rates (<50%) resulted in further low hatchability from such egg batches. Ovarian fluid EC was significantly and positively related to increased occurrence of yolk-sac edema. High quantity of ovarian fluid in egg batches was associated with reduced egg quality in terms of fertilization and hatching rates and occurrence of yolk-sac edema. A cumulative effect of ovarian fluid pH, EC, osmolality, and quantity explained up to 62% of the total variation in fertilization rates. The findings from the present study indicate that parameters measurable at the initial phase of production, in particular ovarian fluid pH and EC, might have a potential for future use as egg quality indicators in hatchery management.

Induced Morphological Changes in Larval Rock Bream, Oplegnathus fasciatus, under Starvation.

Morphological changes in the reared rock bream, Oplegnathus fasciatus, from hatching to six days after hatching were examined during the early growth stage under starvation. All the larvae died within five days when feeding was delayed for three days after hatching. These results imply that initial larval food should be supplied within two days of hatching. Changes in the pectoral angle and the ratios of eye height to head height, gut height to standard length, and gut height to myotome height in the rock bream are alternative indicators for the identification of starving fish. These indicators might prove useful in evaluating the successful transition from endogenous to exogenous feeding in this species.

Hatching time effect on the intra-spawning larval morphology and growth in Northern pike (Esox luciusL.)

Based on the analysis of 11 morphometric variables of body (total length, body area and perimeter, myotome height and eye diameter) and yolk sac (length, height, area, perimeter and volume) of pike larvae, the aim of this study was to evaluate how larval size at hatching and growth of larvae hatched from single egg batches vary according to three hatching times: early, mid and late. Hatching time structures strongly pike larval morphometrics. Early hatched larvae have smaller body sizes at hatch, faster growth and higher yolk use efficiency than late hatched ones. Early hatched larvae seem to be premature and hatch at precocious developmental stage whereas late hatched individuals continue their growth within the egg shell and hatch at larger size but with lower reserves (yolk). A compensatory growth phase was observed for the early hatching pike larvae particularly during the first 5 days post hatch. Consequently, no significant difference in body parameters was recorded from day 10 post hatching whatever the hatching time. The higher growth accomplished by early hatched larvae may be related to a particular metabolic activity that converts more efficiently yolk into body tissues.

Iodine-enriched rotifers and Artemia prevent goitre in Senegalese sole (Solea senegalensis) larvae reared in a recirculation system

To study the effect of dietary supplementation of iodine in Solea senegalensis, larvae were randomly distributed in six tanks. Larvae in three tanks were given rotifers and Artemia enriched with iodine in addition to Rich Advance or Super Selco from 2 days after hatch (DAH) until 31 DAH. Larvae in a second set of three tanks were fed control rotifers and Artemia, enriched only with Rich Advance or Super Selco. Samples were collected at 2, 5, 10, 15 and 31 DAH to determine dry weight, total length, myotome height and thyroid status. Larvae fed the iodine-enriched diet had significantly higher weight at 31 DAH and higher levels of whole body iodine concentration, compared to control larvae. At 31 DAH, larvae from the control treatment showed typical goitrous thyroid follicles. Thyroid cells of larvae from this treatment appeared columnar or afollicular, with the colloid partly or completely depleted, representative of hyperplasia (goitre). The lower growth rate in fish larvae from the control treatment was possibly a consequence of the hyperplasia, and the iodine enrichment prevented Senegalese sole larvae from developing goitre. This study demonstrates the importance of iodine enrichment of live feed for fish reared in a recirculation system.

Effect of prey type and size on the growth, survival and pigmentation of cod (Gadus morhua L.) larvae

The aim of this study was to investigate the effect of natural zooplankton versus rotifers and the effect of prey size on the growth and survival of cod larvae. At 20 days post hatch (DPH) myotome height, standard length and dry mass were significantly higher in larvae fed zooplankton compared to those fed rotifers. The dry mass at age 25 DPH was 135 μg (±45), 331 μg (±114), 391 μg (±121) for larvae fed rotifers, small size and large size plankton, respectively. At 25 days post hatch, the survival rates were 41.8% (±10.5), 90.7% (±2.3) and 91.4% (±1.7) for larvae reared on rotifers, small size and large size plankton, respectively. The limited growth and survival of cod larvae reared on rotifers were not mainly caused by the small size of rotifers. Large differences in skin coloration between larvae in the rotifer group and the two zooplankton groups were observed, probably caused by the large difference in astaxanthin levels in rotifers and natural zooplankton. We suggest that the nutritional composition of rotifers is a limiting factor for cod larvae growth and survival.

Short-term Effects of First-prey Type and Number on Survival and Growth of Intensively Cultured Spotted Seatrout, Cynoscion nebulosus (Sciaenidae), Larvae

Five test diets – 20, 10 rotifers/mL/d, 5 rotifers/mL/d + 3 nauplii/mL/d, 5 and 8 nauplii/mL/d – were used to examine the effect of Acartia tonsa nauplii and a small strain of rotifers on survival, myotome height, notochord length, and condition (myotome height/notochord length) of spotted seatrout, Cynoscion nebulosus, larvae through 6-d posthatch (PH). Diet did not affect survival. Larvae fed 5 and 8 nauplii/mL or 5 rotifers + 3 nauplii were longer, taller, and in better condition than larvae fed either 10 or 20 rotifers/mL. The condition of larvae fed diets with nauplii declined after Day 5 which suggests a shortage of prey in those diets after Day 4 or 5. Although copepod nauplii offer substantial short-term benefits in the culture of spotted seatrout, further study is required to determine the number of nauplii and/or rotifers necessary in the diet beyond Day 4 and to assess the long-term impact of the different diets.

Looking closer at the determining of a phenotype? Compare by stages or size, not age

Summary During ontogeny, individual fish larvae and juveniles will develop at different paces despite apparently identical age and environment, and even genetic background. The urgent need to elucidate mechanisms critical to juvenile production, recruitment or even lifelong growth patterns implies that measures and results are compared by a meaningful standard such as developmental stage of the individual fish. Characterizations of developmental stages based on relatively invariable characteristics such as the sequence of cranial ossification have proven to be not only commercially and scientifically applicable in Atlantic halibut, but also point to a practical use for a character which is preserved in most fishes examined. Once described, useful proxies for stage determinants may be size parameters such as standard length, or preferably myotome height (particularly for flatfishes). The worst proxy for development of a batch of fish is age, exacerbated by the expense of analyzing irrelevant intervals.

Cell cycle analysis of brain cells as a growth index in larval cod at different feeding conditions and temperatures

The percentage of cells dividing in a specific tissue of individual larvae can be estimated by analyzing DNA per cell by flow cytometry. An experimental test was carried out with cod (Gadus morhua) larvae, with brain as the target tissue, to validate this technique as an appropriate growth index for larval fish. Standard length (SL), myotome height, and %S-phase (% of cells in the S-phase of the cell-division cycle) variability were analyzed, with temperature (6 and 10°C), food level (high- and no-food) and larval developmental stage (first feeding, pre-metamorphosis and post-metamorphosis) as independent factors. Cod larvae grew faster (in SL) and presented a higher %S-phase under high-food conditions. Larval SL increased with temperature in rearing and experimental tanks. However, there was a significant interaction between temperature and food in the %S-phase. There were no significant differences in the %S-phase between 6 and 10°C at high-food levels. We suggest that this result is a consequence of temperature-dependency of the duration of the cell cycle. In the absence of food, larvae at 10oC had a lower %S-phase than larvae at 6°C, which may be related to increased metabolic costs with increasing temperature. Considering the effect of temperature, the mean % S-phase explained 74% of the variability in the estimated standard growth rate.

Growth and survival of larval and juvenile cobia Rachycentron canadum in a recirculating raceway system

Cobia Rachycentron canadum is a fast-growing, pelagic marine species that has recently attracted aquaculturists in both the research and commercial sectors. The typical method of grow-out for this species is in outdoor systems where production is limited to locations and seasons conducive for adequate growth and survival. Expanding the culture of cobia to indoor recirculating aquaculture systems (RAS) would allow for the production of fingerlings throughout the year and extend production to cooler regions. Two rearing trials were conducted to examine the growth and survival of cobia from hatching through 4 (trial 1, T1) or 35 (trial 2, T2) g in RAS. Cobia larvae were reared in circular tanks placed in a raceway to control water temperature and quality. During early juvenile grow-out, fish were transferred without grading to a second raceway on 29 dph (T1) or over a period of grading from 29–43 dph (T2). Larval growth (1–22 dph) measured as standard length was similar for both trials ranging from ∼ 3.9 to 14.7 mm. However, larval growth measured as wet weight (0.033 g, T1; 0.026 g, T2) or dry weight (5.7 mg, T1; 3.9 mg, T2) was significantly greater on 22 dph during T1 as was the ratio between myotome height and standard length. These differences may have resulted from an increase in initial densities from 8.7 larvae l − 1 (T1) to 14.7 larvae l − 1 (T2) which apparently caused an increase in food competition and overall aggression. During juvenile grow-out, cobia reached 4.0 g on 43 dph in T1 and 35.4 g on 71 dph in T2 matching weights achieved during grow-out in outdoor ponds. Over the course of both trials, survival was similar to that reported in outdoor ponds. Mean survival (± S.D.) during the early rearing phase (hatching through 29 or 43 dph) averaged 13.2 ± 3.2 % and 10.4 ± 3.2 % corresponding to final densities of 0.9 ± 0.2 and 1.2 ± 0.4 fish/l for T1 and T2, respectively. During the first grow-out phase (29–43 dph), survival of fish moved into the open raceway was 64.5% in T1 and 88.7 % in T2. Survival of cobia during the second grow-out phase (43–71 dph) for T2 was 92.5%. The results of this study indicate that cobia can be successfully cultured in indoor systems from hatching through at least 35 g without negatively affecting growth or survival.

Stock and parental effects on embryonic and early larval development of winter flounder Pseudopleuronectes americanus (Walbaum)

A hierarchical breeding design was used to determine if winter flounder Pseudopleuronectes americanus embryos and yolk‐sac larvae sired by Georges Bank males developed and grew larger than fish sired by Passamaquoddy Bay males, and to examine parental contributions to variations in fertilization success, time to 50% hatch, hatch success and larval morphological development. Significant stock effects were detected for time to hatch and larval development. Eggs fertilized by Passamaquoddy Bay males reached 50% hatch significantly earlier than eggs fertilized by Georges Bank males. Larvae sired by Georges Bank males were significantly larger during larval development for four of the six traits measured at 12 days post‐hatch: head depth, jaw length, myotome height and body area. Embryo and larval development were strongly influenced by maternal contributions; there were significant maternal variance components for the majority of the variables measured. Paternal variance components were significant for fertilization success, time to hatch, larval jaw length and larval head depth, however, they acted principally through parental interactions. This information has important implications for the long‐term sustainable development of winter flounder for aquaculture purposes as well as for understanding winter flounder genetic variation in the wild.

Evaluation of new microparticulate diets for early weaning of Atlantic cod ( Gadus morhua): Implications on larval performances and tank hygiene

In recent years, interest in the intensive culture of Atlantic cod ( Gadus morhua) has increased dramatically due to several factors including a reduced supply of cod from capture fisheries, a high market price for wild cod and the suitability of the species for culture. One of the major problems facing the industry has been the high cost and unreliability of live feeds, specifically the live feed Artemia. The main objective of this project was to determine whether Artemia use could be reduced or replaced completely with two novel microparticulate diets (MPD's), without negatively compromising growth, survival performance and tank hygiene under simulated commercial conditions. The experiment consisted of four treatments, a live feed control treatment (group A), a 50% Artemia replacement treatment with MPD-1 (group B), a 100% Artemia replacement treatment with MPD-1 (group C) and a 100% Artemia replacement treatment with MPD-2 (group D). All treatments were run in triplicate. Growth performances, development (standard length, eye diameter, myotome height and wet weight), water quality (bacteriology and spectrophotometry) and survival were measured throughout the duration of the trial. The results of the experiment indicate that the treatments containing Artemia (groups A and B) both achieved significantly higher growth rates than treatments that did not contain Artemia (groups C and D). The highest survival rates achieved at 70 dph were in treatments A and D (13.8% ± 0.7% and 14.2% ± 2.1% respectively) when compared to treatments B and C (11.8% ± 0.3% and 5.5% ± 1.3% respectively). Survival was also significantly higher in treatment B than in treatment C. This study demonstrates that while the best growth and survival rates are still achieved when cod larvae are fed Artemia, combining live feeds and commercially available MPD's (co-feeding) can produce comparable growth and survival rates thus potentially reducing the reliance on live feeds. However the complete replacement of Artemia with MPD's still significantly reduced growth potential suggesting that the nutritional composition of MPD's, requires further investigation.

Development of the axial skeleton and skeletal abnormalities of Atlantic halibut (Hippoglossus hippoglossus) from first feeding through metamorphosis

Larval Atlantic halibut (Hippoglossus hippoglossus) were sampled from a commercial hatchery to observe skeletal abnormalities throughout development and to develop a metamorphic stage definition utilizing order of vertebral ossifications in combination with ossification events of the cranium. Using a whole mount cartilage and bone staining technique, skeletal abnormalities were classified and quantified into 21 types and the order of ossification events determined. During metamorphic development, stage 5 fish lacked calcified vertebral elements. Stage 6 was characterized by ossification of the exterior perimeter of vertebrae and attachment points of neural and hemal spines within the prehemal and posterior hemal regions. Further calcification of the vertebral column extends cephalad and caudad from the origin of ossification during stage 7. In stage 8, the vertebral column and caudal fin bones are weakly ossified but showing full ossification by stage 9. There was a high correlation between age (R2=0.964), standard length (R2=0.996), and myotome height (R2=0.994) with stage. Rapid development occurring over a short period of time while in the prometamorphic stages of development, may give rise to the presence of serious skeletal abnormalities in later development. The highest frequency of skeletal abnormalities occurred in the prehemal region, followed by the hemal region despite developmental stage. Hypertrophic vertebrae in the prehemal region are present in earlier developing larvae, and pre- to pro-metamorphic. Skeletal abnormalities commonly begin during stage 6 and 7, when the majority of the vertebral elements are ossifying. Studies on the immunohistochemistry and biochemical processes involved in bone growth may be useful to determine the causative factors of skeletal abnormalities.

Parental effects on early life history traits of haddock Melanogrammus aeglefinus

Abstract Gametes from five male and three female haddock (Melanogrammus aeglefinus) were crossed to produce 15 half-sibling families that were used to evaluate potential parental contributions to early life history variability. Larval morphology at 0 and 5 days post-hatch (dph) and time to starvation in the absence of food were examined. Maternal influences on larval standard length and yolk area were significant at 0 and 5 dph. Paternal effects on larval standard length were significant at 0 and 5 dph, whereas paternal effects on yolk area were only significant at 5 dph. Larval eye diameter was influenced by maternity at day 0 post-hatch and by both maternity and paternity at 5 dph. Myotome height of larvae was subject to maternal and paternal influences at 0 and 5 dph. Growth rate was significantly influenced by both paternity and maternity. Yolk utilization efficiency was significantly influenced by parental interaction, while the time taken for larvae to die in the absence of food was affected only by maternity. Results of this study not only confirm the importance of female contributions to larval development but also indicate a paternal influence on the development and the early life history success of marine fish.

Effects of egg size, food supply and spawning time on early life history success of haddock Melanogrammus aeglefinus

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 285:169-180 (2005) - doi:10.3354/meps285169 Effects of egg size, food supply and spawning time on early life history success of haddock Melanogrammus aeglefinus R. M. Rideout1,2,3,*, E. A. Trippel1, M. K. Litvak2 1Biological Station, Fisheries and Oceans Canada, 531 Brandy Cove Road, St. Andrews, New Brunswick E5B 2L9, Canada 2Department of Biology and Centre for Coastal Studies and Aquaculture, University of New Brunswick Saint John, New Brunswick E2L 4L5, Canada 3Present address: Fisheries Conservation Group, Marine Institute of Memorial University of Newfoundland, PO Box 4920, St. John’s, Newfoundland A1C 5R3, Canada *Email: rick.rideout@mi.mun.ca ABSTRACT: Eggs and larvae produced by pairs of spawning haddock Melanogrammus aeglefinus were monitored between 2001 and 2003 to determine the effects of spawning time, egg size and food supply on early life history success. Females usually released eggs at 3 d intervals. All females exhibited a continuous decrease in egg diameter and dry weight with consecutive batches, but the decrease in size did not influence fertilization or hatching success. Larval size (standard length and dry weight), yolk area, eye diameter, myotome height, and finfold area were all positively related to egg size and therefore decreased between early- and late-season larvae produced by the same spawning pairs. Differences in larval morphology persisted for at least the first 5 d after hatching. Jaws were not developed at hatching (5°C), but jaw length did show a strong positive relationship with egg size at 5 d post-hatch (dph). The ability of newly hatched larvae to withstand periods of starvation was directly related to initial egg size. Under high prey abundance (5000 l-1) larval survival to 20 dph was highly variable (1.8 to 50.7%) with no differences in survivorship or specific growth rate (0.818 to 0.936% d-1 in standard length) for larvae from early-, middle- and late-season egg batches. With low prey density (1000 l-1) survival of larvae from late-season egg batches was significantly lower (0.4%) than those from early egg batches (1.8%). No differences in larval specific growth rate existed between early and late batches, but growth rate was reduced in both cases with low food abundance (0.683 to 0.690 d-1 in standard length). Results suggest that smaller larvae produced late in the spawning season have reduced feeding capabilities and may experience lower survivorship in the ocean than larger, early-season larvae. KEY WORDS: Haddock · Spawning time · Egg size · Larvae · Prey density · Early life history success · Recruitment Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 285. Online publication date: January 19, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Staging of Atlantic halibut ( Hippoglossus hippoglossus L.) from first feeding through metamorphosis, including cranial ossification independent of eye migration

To determine developmental stages independent of eye migration, a highly plastic feature in Atlantic halibut, 180 sibling halibut larvae reared at an average temperature of 11.9 °C from first feeding and for a further 46 days were examined, cleared and stained for ossification and the cranial development was recorded. Morphological development and cranial ossification generally coincided. The order of ossification of cranial structures was: jaw structures, hyoid arch, opercular bones and structures of the neurocranium. The Frontale exhibited torsion correlated with eye migration, but calcification began earlier and full calcification was independent of ocular displacement. The appearance of ossified elements was used to group larvae into Stages 5–9, comprising premetamorphosis to climax metamorphosis, with significant morphometric differences between stages. The trajectory of juvenile development appears fixed by Stage 8. There was a linear relationship between stage and myotome height ( R 2=0.86) and stage and standard length ( R 2=0.80). The stage definitions were validated on two groups ( n=23, n=101) of commercially produced larvae. Because metamorphosis is protracted in halibut, use of these stages and especially myotome height should help standardize sampling and analysis between experiments and between producers.

Paternal effects on haddock early life history traits

Paternal effects on haddock Melanogrammus aeglefinus early life history traits were examined by crossing eggs and sperm in a nested design and analysing the progeny at 0, 5 and 10 days post‐hatch (dph). The proportion of the variance in early life history traits that was due to paternity was significant for hatching success, larval standard length, myotome height, jaw length and yolk size, but not eye diameter or yolk utilization efficiency. Some morphological traits were influenced more by paternity than maternity. The findings suggest that the importance of males in the early life history success of marine fishes be reconsidered.

Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvae

Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c. 17° C. Non‐fed fish reached irreversible starvation at age 5 DAH. Non‐fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non‐fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non‐fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two‐thirds to three‐quarters of the overall mortality (46–52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non‐fed larvae accounted for about a third of the overall mortality (100%).