Early ontogeny of Pimelodus blochii Valenciennes, 1840 (Siluriformes: Pimelodidae): Neotropical catfish

Larval ontogeny of the long-whiskered catfish Pimelodus blochii Valenciennes, 1840 is described, providing useful characters for identification and determining the growth pattern throughout its development. Eighty-nine larvae classified in three stages (preflexion, flexion and postflexion) and 30 juveniles were analyzed, totaling 119 individuals. The specimens were collected monthly from January 2013 to May 2019 in the lower Amazon river. A suite of morphological, morphometric, and meristic data was used to describe the stages of development. Three analytical regression models were used: simple linear, quadratic and piecewise regressions. The larvae are characterized by small to moderate eyes, subinferior mouth, and long barbels (maxillary larger than the mental barbels), triangular-shaped adipose fin, and the final part of the intestine reaching half the body. Pigmentation consists of dendritic chromatophores distributed irregularly in the body, ventral region and head, intensifying in the flanks and dorsal region throughout development. The total number of myomeres has a mode of 42 muscle bundles, ranging from 40 to 42 (15 to 16 pre-and 25 to 26 post-anal) and the number of fin segments corresponded to: pectoral = I + 9, pelvic = 6, dorsal = I + 6 and anal = 11–12. All body variables showed discontinuous isometric growth, indicating a deceleration in the structural modeling of the body, between the flexion/post-flexion stages and acceleration in post-flexion/early juvenile period. Precisely when the formation of the fin rays, muscles and organs of the digestive system and ossification are observed, suggesting low morphological variation during ontogenetic development. Pimelodus blochii differs from other congeneric species in the lower Amazon river by meristic characters, which helps to correctly identify individuals in early stages of development.

The Development of Strain Typical Defensive Patterns in the Play Fighting of Laboratory Rats

During play fighting, rats attack and defend the nape, which if contacted is nuzzled with the snout. While all strains of rats can use all defensive tactics to protect the nape, there are strain-typical preferences for using particular tactics This study tests two hypotheses for this strain difference: (1) that each strain has strain-specific thresholds for each tactic, or (2) that each strain attacks differently which leads to strain differences in which defense tactics are used. Juvenile Long-Evans and Sprague-Dawley males were tested with both unfamiliar (experiment 1) and familiar (experiment 2) same-strain and different-strain partners. Experiment two was conducted to determine if familiarity with a different strain might allow rats to modify their strain-typical pattern of play. If hypothesis (1) were true, they would maintain strain-typical defense patterns irrespective of partner strain, whereas for (2) it would vary with partner strain. Hypothesis (1) was supported in the first experiment; all the rats maintained their strain-typical patterns regardless of the partner’s strain. However, the second experiment supported neither hypothesis, as each animal displayed strain-divergent behavior when playing with partners of a different strain as well as with partners of the same strain. Given that in the second experiment subjects were reared in mixed-strain groups, it is possible that, during the early juvenile period, animals are susceptible to discordant social experiences

Variation in the growth of larval and juvenile snapper, Chrysophrys auratus (Sparidae)

For many fish species, growth and mortality of larvae are closely coupled, with faster-growing larvae generally experiencing higher survivorship in the plankton, which may lead to higher recruitment. Using back-calculated growth trajectories derived from otolith increments we used the modified Fry model to estimate the growth rate of larvae and early juveniles of the commercially important sparid, Chrysophrys auratus, at four sites around northern New Zealand. Back-calculated growth rates were used to test the hypothesis that fish with a short pelagic larval duration (≤20 days) grew faster than did fish with a long pelagic larval duration (>24 days) during both the larval and juvenile periods. At three of the four sites, fish with a short larval duration grew significantly faster during the larval period, and these larvae generally continued to have a larger size-at-age as juveniles up to 70-day-old. Growth rates for both the larval and early juvenile period were also found to vary significantly among the four sites and were found to be unrelated to differences in water temperature. Localised variation in early growth of C. auratus among sites may be important in helping explain differences in their contribution to the recruitment to C. auratus populations.

Growth of sterlet Acipenser ruthenus under experimental and farm conditions of the Czech Republic, with remarks on other sturgeons

Growth rate of sterlet (Acipenser ruthenus) juveniles and adults was studied and compared with other sturgeon species under experimental and farm conditions in the Czech Republic. During the juvenile development (0+ to 5+) the specific growth rate (SGR) decreased successively from 17.67 to 0.05 %.d−1. During the adult period of development (6+ to 13+), the SGR fluctuated from 0.0191 to 0.0562, mean = 0.0410 %.d−1. In addition, body weight condition and length-weight relationship are presented. The adult period commenced at average age from 4 to 5 years. At the end of subsequent 13 years of life (1st–13th), following values of TL/w (in mm/g) in reared sterlet were determined: 250/53, 350/174, 400/250, 440/320, 465/400, 490/462, 516/525, 546/645, 561/720, 596/860, 610/1014, 625/1199, 660/1456. A very fast growth intensity was determined in the young sterlet (1st and 2nd year) while it decreased in the older fish. Growth intensity of other reared greater sturgeon species (Huso huso, Polyodon spathula, A. gueldenstaedtii, A baerii, A. stellatus), compared with sterlet in early juvenile period of ontogeny, were mainly higher.

Carry-over effects in brown trout (Salmo trutta): hypoxia on embryos impairs predator avoidance by alevins in experimental channels

Laboratory experiments on brown trout (Salmo trutta) embryos suggest that sublethal stress in the gravel nest such as hypoxia may alter the behaviour and survival of fish during the early juvenile period. Eggs and embryos were incubated at constant temperature (8.2 °C ± 0.6 standard deviation) under nonlethal dissolved oxygen (DO) concentrations (3.0 mg·L–1; 26% air saturation level) and normoxia (10.3 mg·L–1 DO; 90% air saturation level). The average survival from fertilization to end of embryonic development was 70% and 85% for hypoxic and normoxic groups, respectively. Hypoxic embryos grew slowly compared with their normoxic counterparts, but similar body sizes were observed when yolk-sac absorption was completed. Fish incubated as hypoxic embryos delayed their emergence from the gravel in experimental channels. In presence of freshwater sculpin (Cottus gobio), their swimming activity was reduced by 20%, on average, and predation was enhanced by 14% compared with normoxic groups. Results support the view that subtle events early in a fish's ontogeny can have carry-over effects on later periods of its life cycle, and this phenomenon may be a significant source of variation in salmonid fitness.

The Ecology of Juvenile Salmon in the Northeast Pacific Ocean: Regional Comparisons

Abstract.—Research on the ecology of salmon in the northeast Pacific Ocean began in the early 20th century. Charles Gilbert and Willis Rich demonstrated the basis for the stock concept and were instrumental in changing common misconceptions of the times. Later in the 1900s, research endeavors, primarily under the auspices of the International North Pacific Fisheries Commission, led to important studies on the distribution and migration of maturing salmon on the high seas. Research on the early juvenile period was initiated later, especially after the 1982–1983 El Niño clearly showed the limits of the ocean’s carrying capacity along the west coast of the United States. There is now good evidence for both intra- and interspecific competition among salmon in the open ocean and for correlations between variable physical environments, such as El Niños and regime shifts, and survival of salmon during early ocean life. How mortality rates are affected by physical forcing, food availability, predation, and food web structure and how these effects will be modified by climate change and global warming are all major challenges for the future.

Body mass, spleen mass and level of thyroid hormones in juvenile hypothyroid rats

In this paper, the effect of hypothyroidism on body mass and spleen mass of rats was examined during the prenatal and early juvenile periods. Hypothyroidism was induced by the application of propylthiouracil (PTU) in drinking water to the mothers from the first day of gravidity and during lactation, and the offspring were sacrificed on the 14th and 21st days after birth. The body mass of the juvenile rats was measured just before they were sacrificed. The concentrations of triiodothyronine (T3) and thyroxine (T4) in blood serum were determined in control and treated juvenile rats. The results indicate that PTU leads to a reduction in T3 and T4 serum concentrations in treated juvenile rats. Treated juvenile rats had a bigger body mass and spleen mass in comparison with control animals. These data indicate that hypothyroidism induced in the prenatal and early juvenile period leads to an increase in the body mass and spleen mass and disrupts the normal development of the spleen in the course of the examined period. .