Larval Standard Length Research Articles

An individual‐based model for the direct conversion of otolith into somatic growth rates

ABSTRACTOtolith increment width and larval fish data (length and weight) were used to develop an individual‐based model (IBM) to describe daily resolved growth rates of North Sea herring (Clupea harengus) larvae (Autumn Spawners) caught during International Herring Larvae Surveys in the ICES area IVa from 1990 to 1998. The model combines sagittal otolith readings (core and individual increment measurements), larval standard length and weight data, and solves an over‐determined set of linear system equations for all parameters using the method of least square residuals. The model consists of a matrix, which describes the increment width formation of 119 larvae, a vector containing their length/weight measurements, and a vector describing residuals. The solution vector yields age‐dependent maximum somatic growth rates of herring larvae up to an age of 41 days with sizes ranging from 10 to 25 mm. The observed environmental temperature in which larvae dwelled was relatively uniform. Therefore, measured increment width was individually used to determine daily growth from any single larva in relation to their potential maximum growth under optimal feeding conditions. The results are discussed with respect to the spatial and temporal variability of larval occurrence. Finally, an analysis of error estimation of the larval growth characteristics is presented.

Evaluation of Fatty Acid Enrichment of Live Food for Yellowtail Snapper Ocyurus chrysurus Larvae

Abstract— The purpose of this study was to examine the effect of varying dietary levels of highly unsaturated fatty acids (HUFA) in Live prey on the standard length, specific growth rate, survival, and fatty acid composition of yellowtail snapper Ocyurus chrysurus larvae. Two experiments were conducted utilizing rotifers and Artemiu enriched with live algae (Isochrysis galbana or Nannochloris oculata) or commercial preparations (Aquagrow Advantage, Aquagrow Advantage plus Aquagrow arachidonic acid, and Algarnac 2000). Larval growth and fatty acid composition were evaluated during the rotifer, Brachionus plicatilis, and Artemia feeding periods and survival rates were calculated at the termination of each trial (18 or 20 d after hatching). In general, prey enriched with the commercial products contained higher levels of docosahexaenoic acid, eicosapentaenoic acid, n-3 HUFA, and × HUFA than those enriched with live algae. The addition of arachidonic acid to the Aquagrow Advantage enrichment medium significantly increased the amount of this fatty acid in rotifers but not in Artemia. At the end of the growth trials, larval standard length was highest when larvae were fed prey enriched with I. galbanu (6.4 mm) or commercial preparations (6.7–7.1 mm) versus N. oculatu (5.2 mm). Furthermore, larvae fed prey enriched with commercial preparations had significantly (P < 0.05) higher survival rates (2.2-5.9%) than those fed prey enriched with live algae (1.1-1.4%). These results suggest that yellowtail snapper larvae require dietary levels of HUFA beyond those achieved by enriching prey with live N. oculata or I. galbana

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.

Maternal and paternal influences on early life history traits and processes of Baltic cod Gadus morhua

Embryo survival, larval standard length, yolk-sac area, yolk utilization and resistance to starvation were significantly influenced by the female parent and the interaction between both parents of Baltic Sea cod Gadus morhua in a gamete factorial cross of 3 females and 5 males in all possible combinations. The proportion of variance in embryonic survivorship that was due to maternity during incubation was significant during the first 4 d, but was insignificant during the 5 to 9 d interval. During the 5 to 9 d interval, the male–female interaction was significant. Standard lengths at hatch and 5 d post hatch and specific growth rate of unfed yolk-sac larvae were strongly influenced by the female. Equivalent amounts of variation in larval resistance to starvation were explained by maternity and bi-parental interaction. Paternity alone did not explain a significant amount of variation for the traits or processes examined. The bi-parental interactions reported demonstrate a female’s choice of mate could significantly influence the early life survivorship of Baltic cod offspring.

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.

Growth pattern and growth dependent mortality of larval and pelagic juvenile North Sea cod Gadus morhua

We investigated growth patterns and evidence of growth dependent survival for a pop- ulation of Atlantic cod Gadus morhua using analysis of their otolith microstructure. Central concen- trations of a population of cod larvae and juveniles in the north-eastern North Sea were sampled twice (in April and May 2001), and larval/juvenile growth history from each of the sampling sequences was outlined. Growth rate was estimated by fitting a Laird-Gompertz equation to lengths- at-age, and we found the mean specific growth rate in length at age 20 d was 3.2% d -1 , declining to 1.9% d -1 at an age of 90 d. Otolith radius and larval standard length were highly correlated, and otolith growth was used as a measure of larval somatic growth. The larvae were divided into 3 groups dependent on their hatch-date, and for each hatch group, the same period of past growth was com- pared between fish sampled in April and May. A 2-way repeated-measurement ANOVA revealed a significant higher past growth of fish sampled in May in 2 of the 3 hatch-groups, implying a higher mortality of the slow growing larvae. Additionally, otolith size at age differed significantly between the April and May sampling of the oldest larvae. Using the obtained information we illustrate the consequences of being larger at age by nonparametric spline functions. These show up to 10-fold differences in the relative survival probabilities between cod of smallest or largest size at age, suggesting that mortality can be strongly dependent on growth.

Effects of environmental temperature on the development of the myotomal white muscle in larval carp (Cyprinus carpio L.).

A study was conducted on common carp (Cyprinus carpio L.) to determine the effects of environmental temperature experienced by embryos and larvae on the development of myotomal white muscle. Eggs from one female were divided into two groups following fertilisation and incubated at constant pre-hatch temperatures of 18 or 28 degrees C. At hatching, larvae from the 18 degrees C-incubated eggs were divided into two groups and either reared at the same temperature of 18 degrees C ('cold' group) or transferred over a period of 5 days (at 2 degrees C per day) to 28 degrees C ('transferred' group). Larvae hatched from eggs incubated at 28 degrees C were reared at the same temperature of 28 degrees C ('warm' group). Larvae were sampled at two developmental stages (stage 1, inflation of the back chamber of the swimbladder; stage 2, inflation of the front chamber of the swimbladder) and at 26 days post-hatching. The maturation of myotome shape during larval life was studied in parallel with the changes occurring in the organisation of white fibres. At stage 1, the epaxial part of the myotomes surrounding the vent had the shape of lamellae inclined backwards, and only one central layer of white fibres was present. At stage 2, the epaxial part of the myotomes began to acquire a V-shape, which was well developed at 26 days post-hatch. At stage 2 and at 26 days post-hatch, two layers of white fibres were identified: the initial central layer and a second apical layer. These differ in their orientation, the initial central layer being orientated backwards and the apical layer forwards, and in the mean fibre diameter, which is greater in the initial central layer. Studies on the effects of temperature (constant 18 degrees C, constant 28 degrees C, transfer from 18 to 28 degrees C at hatching) were carried out according to both the developmental stage and the length of the larvae. At stage 1, no significant differences were found between the three groups for larval standard length and muscle variables. The number of fibres in one quadrant of epaxial white muscle sectioned at the level of the vent was 100-111. At stage 2, there were significant differences between groups. Larval standard length and mass were higher in the cold group than in the warm group. The transferred larvae were of intermediate standard length but had a significantly higher cross-sectional area of white muscle than either of the other two groups. This increase in surface area was related to a 50 % greater fibre number (233) in the transferred larvae compared with the cold (165) or the warm (152) larvae. The increase in fibre number was more marked for large-diameter ( >20 microm) white fibres located in the initial central fibre layer (+58-72 % in transferred larvae) than in small-diameter ((less than equal to) 10 microm) white fibres mainly located in the apical layer (+18-35 %). In 26 days post-hatch samples, transferred larvae still showed a higher total number of white fibres than warm larvae, but the difference was no longer significant when the total number of white fibres was regressed against larval standard length, suggesting that this stimulation may be temporary.

Muscle growth and development in Atlantic cod larvae (Gadus morhua L.), related to different somatic growth rates.

The present study describes the development of the axial musculature in first-feeding larvae of Atlantic cod (Gadus morhua L.) with different somatic growth rates achieved by using different nutritional conditions. Muscle growth was assessed by determining the number of muscle fibres (hyperplasia) and the growth of existing fibres (hypertrophy). Larvae were fed rotifers containing a high (1. 4; treatment 1) or low (0.2; treatment 2) ratio of docosahexaenoic acid to eicosapentaenoic acid from day 5 after hatching. From day 17, the larvae were fed Artemia nauplii with the same enrichment in both treatments. Treatment 1 gave the highest somatic growth rate and hence the highest dry mass at the end of the experiment, but no difference in larval standard length was found between treatments. In slow-growing larvae, higher priority was thus put into reaching a certain length than into increasing muscle mass. The largest fibres, which were present from hatching, increased in cross-sectional area during larval development, but no differences were found between treatments in the cross-sectional area of individual fibres or the total cross-sectional area of these fibres at the end of the experiment. The first white recruitment fibres were observed at the dorsal and ventral apices of the myotome at approximately the onset of first feeding (larval length 4.5 mm). In larvae 8.5 mm long, the total cross-sectional area of white muscle fibres in the treatment 2 group was 75 % of that in the treatment 1 group. The highest somatic growth rate was associated with an increased contribution of hyperplasia to axial white muscle growth. In the faster-growing larval group, the relative contribution of hyperplasia to the total white muscle cross-sectional area was 50 %, whereas it was 41 % in the slower-growing larval group. The subsequent growth potential may thus be negatively affected by inadequate larval feeding.

Maternal, paternal and temperature effects on otolith size of young herring ( Clupea harengus L.) larvae

Investigations were carried out to clarify the timing of first check formation, and the influence of maternal, paternal and temperature effects on otolith size of young herring larvae. Three male and three female herring of the Norwegian spring-spawning-herring-stock were used as parental fish in a 3×3 factorial design, resulting in nine parental combinations. Eggs from each of the combinations were incubated at 4, 8 and 12°C. Larvae were sampled at two ontogenetic stages: newly hatched and at the end of the yolk sac (EYS) stage. In addition, some larvae were also reared with wild zooplankton and sampled 16–21 days after hatching to compare first check size with observed otolith size of unfed larvae. The first check was deposited 1–2 days after hatching and before onset of exogenous feeding at 12°C. Significant maternal and temperature effects were observed on the size of sagitta and lapillus at hatching, with smaller otoliths at higher temperatures. Larval length showed a similar temperature response as the otoliths, whereas larval dry mass showed an opposite trend. Otolith size and larval length and mass were poorly correlated, and large variability in the otolith data were evident. Temperature also influenced the measured variables at the EYS stage while the maternal influence was not as strong as at hatching. No sagittal growth between hatching and the EYS stage was observed at 4°C although larval standard length increased. Large variability limits the direct application of the first check size as a reliable tool for discrimination of units within and between fish stocks.

An individual-based analysis of the variability of eggs and their newly hatched larvae of Atlantic cod (Gadus morhua) on the Scotian Shelf

We assessed the seasonal pattern of size variation in cod eggs on the Scotian Shelf region of the Northwest Atlantic during the period March 1991–May 1993. Cod eggs were present from October to May during the surveys. Spawning was not strongly bimodal. There was a dominant autumn peak, in contrast to the historically dominant spring spawning. Egg diameter varied seasonally. Seasonal temperature patterns explained 52% of the variation in egg diameter. By incubating the eggs on-board ship, we also assessed the seasonality of the standard length (SL) of larvae that hatched from these eggs. Larval SL also varied seasonally. Egg diameter and SL were significantly correlated, but the correlation was weak (r2 = 0.3). However, the strength of correlation was consistent with laboratory estimates based on individual data. The results suggest that previous estimates of the egg size – larval size correlations are inflated. Temperature exerted a significant effect on both egg diameter and larval size, and is hypothesized to be the agent responsible for the observed seasonal variation.