Post-hatch Larvae Research Articles

EFFECTS OF THE HEAVY METAL, ZINC, ON THE FRESHWATER FISH TILAPIA NILOTICA L.

Gills, gonads, and blood of Tilapia nilotica exposed to different concentrations of zinc sulfate (ZnSO4. 7H2O) exhibited histological effects. Gills of posthatch larvae exposed chronically for 21 days to 2 ppm zinc sulfate and fingerlings to 10 ppm sublethal zinc concentrations exhibited hyperplasia that resulted in fusion of adjacent secondary gill lamellae. The same effects were observed in 4-hour short-term exposure to 30 ppm lethal dose. Posthatch larvae subjected to 2 and 5 ppm sublethal levels of zinc for 30 days retained undifferentiated gonads with differentiation with oogonial proliferation. Ovaries of control fish demonstrated healthy oocyte growth and other normal histological features after 57 days. In contrast, ovaries in treated groups exhibited excessive amounts of connective tissue, hyperemia and markedly reduced oocyte number. Oocytes had wavy irregular surface outlines. Deviation from normal was observed to be dose dependent. In juvenile tilapia, spermatogenesis was observed in control testes. Testes of zinc-exposed fish, on the other hand, remained immature. Hyperemia was markedly pronounced in both testes and ovary after 90 days exposure to zinc. Blood of Tilapia nilotica fingerlings exposed to sublethal concentrations of 2, 5, and 10 ppm zinc for 30, 60, and 90 days exhibited anisocytosis and poikilocytosis. There was an increase in hematocrit values in zinc-reared fish which, however, reverted to control/near control levels at day 90. Hemoglobin values were inversely proportional to the level of zinc in the rearing water. The marked reduction in hemoglobin values in fish reared at the higher zinc concentrations of 5 and 10 ppm suggests the development of some degree of anemia which is also supported by the observations of anisocytosis and poikilocytosis.

Threat-sensitive foraging by larval threespine sticklebacks (Gasterosteus aculeatus)

The threat-sensitive predator avoidance hypothesis predicts that prey can assess the relative threat posed by a predator and adjust their behaviour to reflect the magnitude of the threat. We tested the ability of larval threespine sticklebacks to adjust their foraging in the presence of predators by exposing them to conspecific predators of various sizes and recording their foraging and predator avoidance behaviours. Larvae (<30 days post-hatch) displayed predator escape behaviours only towards attacking predators. At 3 weeks post-hatch larvae approached the predator after fleeing, a behaviour which may be the precursor to predator inspection. Larvae reduced foraging and spent less time in the proximity of large and medium-sized predators compared to small predators. The reduction in foraging was negatively correlated to the predator/larva size ratio, indicating that larvae increased their foraging as they increased in size relative to the predator. We conclude that larval sticklebacks can assess the threat of predation early in their ontogeny and adjust their behaviour accordingly.

Vulnerability of striped bass Morone saxatilis Waldbaum eggs and larvae to predation by juvenile white perch Morone americana Gmelin

Striped bass Morone saxatilis Waldbaum early life stages and juvenile congeneric white perch M. americana Gmelin co-occur in Chesapeake Bay tributaries. Vulnerabilities of striped bass eggs and laboratory-reared larvae to predation by juvenile (58–65 mm total length) white perch were determined. Predation experiments of 15-min duration were carried out in 76-1 tanks with individual predators. Vulnerability of striped bass larvae was directly related to light level in the range 0–1000 lux, but turbidity level (0–15 NTU) had no effect on vulnerability. Eggs and larvae that were progeny of large or small female striped bass, and which differed in size-at-age, were found to be equally vulnerable to white perch predation. Predation rate on eggs was relatively low (1.7·15 min −1), increased on yolk-sac larvae (7.3·15 min −1) and was highest (13.1·15 min −1) on 12-day posthatch larvae, after which it declined. Larvae of 7.0–7.9 mm standard length and 0.25–0.49 mg dry wt were most vulnerable. Predation by white perch on striped bass eggs and larvae potentially is a significant cause of mortality in Chesapeake Bay tributaries, although additional laboratory and field experiments are needed to quantify its impact.

Acute sensitivity of early life stages of fathead minnow ( pimephales promelas) to acid and aluminum

Fathead minnow ( Pimephales promelas) 1-d post-hatch larvae, 12-d post-hatch larvae, and 4-wk post-hatch juveniles were exposed to combinations of acid and inorganic aluminum (Al) for 96 h in the laboratory. Life stages were exposed, under flow-through conditions, to four nominal pH levels: 4.5, 5.5, 6.5, 7.5 (control) and five nominal Al concentrations: 0 (control), 50, 100, 200, 400 μg/l in fresh water with a total hardness of 20–24 mg/l as CaCO 3. Theoretical speciation of the measured total dissolved monomeric Al was performed in order to estimate the toxic forms of Al. The ranking of life stage sensitivities to acid alone was 1-d larvae, most sensitive, followed by 12-d larvae and juveniles. At pH 4.5, all three stages exhibited 100% mortality in all Al treatments and controls. At pH 5.5, 90–100% mortality occurred in all but the 50 μg/l Al treatment and the no Al control. At that pH, hydroxoid species of Al were the predominate forms of the total dissolved monomeric aluminum. At pH 6.5 and 7.5, Al was not toxic to the 1-d larvae and juveniles, but the mortality of 12-d larvae exposed to Al (predominately hydroxy species) ranged from 18 to 68% with no clear dose response.

Ciliary band formation in the doliolaria larva of Florometra

ABSTRACT The development of ciliary band pattern in the doliolaria larva of Florometra serratissima is described based on scanning and transmission electron microscopy. The uniformly ciliated epithelium of the post-hatching larva develops four regularly spaced bands over a period of approx. 20 h generating an epithelial pattern that is, essentially, a series of stripes. The first visible events of pattern formation progress over the larval surface in a posterior-to-anterior and dorsal-to-ventral sequence, but the initial pattern is not, in fact, striped. It instead consists of a close-packed array of oval interband domains separated and surrounded by belts of band cells. Secondarily the interband domains expand laterally and coalesce to form continuous, broad stripes, while the bands remain as narrow stripes between them. Two possible explanations for this unusual sequence of events are discussed: (1) that it can be understood in evolutionary terms with reference to band pattern in other echinoderm larvae, and (2) that it is a morphogenetic necessity because limitations inherent in the patterning mechanism prevent the direct formation of regular stripes.

Chlorine-Induced Mortality of Eggs and Larvae of Spotted Seatrout (Cynoscion nebulosus)

The acute lethal effects of sodium hypochlorite, chloramine, and 5-chlorouracil on eggs and larvae of spotted seatrout, Cynoscion nebulosus, are presented. Forty-eight-h median tolerance limits (TLm) for the various toxicants and age classes (2-h-old eggs, 10-h eggs, and 1-h posthatch larvae) were, respectively: sodium hypochlorite—0.21 ± 0.01, 0.21 ± 0.01, 0.17 ± 0.28 ppm; chloramine—14.14 ± 1.13, 0.57 ± 0.28, 5.75 ± 3.01 ppm; 5-chlorouracil-8.91 ± 1.03, > 100, 79.43 ± 44.97 ppm. The 48-h TLm varied depending on toxicant and age class.

The development and fine structure of the ultimobranchial glands in larval Rana temporaria L.

The fine structure of ultimobranchial (UB) gland cells from Rana temporaria larvae 48 h after hatching until the completion of metamorphosis is described. A single UB cell type is present, believed to be the characteristic C cell, in which secretory granules are first detectable in 8 day post-hatching larvae. These secretory granules show an intimate association with lipid droplets. Unusual membranous and crystalloid inclusions, which may represent yolk platelets, are found in UB glands of very small larvae. The significance of a range of UB organelles is discussed and some scanning electron micrographs presented. This report is believed to be the first published ultrastructural and scanning electron microscope study of larval anuran UB glands.

Protein synthesis in frog embryos and frog liver preparations, and its inhibition by embryo components.

SummaryThe capacity to carry out activities related to protein synthesis has been studied in developing frog embryos and post hatching larvae. Rapid incorporation of labeled amino acids from the external medium into protein could be demonstrated with intact larvae about 5 days before a net increase of total protein was found. Only minor incorporation of labeled amino acid into protein was obtained with cell-free preparations from frog embryos and larvae, even at developmental stages when the total protein content was increasing; however, these preparations did possess a high capacity for amino acid activation. In contrast, analogous cell-free fractions from adult frog liver contained an active system for incorporation of phenylalanine or of an amino acid mixture into protein; the characteristics of the frog liver system were similar to those of cell-free systems for amino acid incorporation described in other species. The low incorporating activity of cell-free preparations from frog embryos or larvae was...