Morphological indices and otolith microstructure of Atlantic croaker,Micropogonias undulatus,as indicators of habitat quality along an estuarine pollution gradient

Synopsis Atlantic croaker, Micropogonias undulatus, sampled from a transect along a pollution gradient show a trend of declining growth and physical condition. This trend is apparent in the mean size of 0-group croaker, in their recent growth rate measured by marginal otolith increment widths, in longer term growth rate as indicated by relative otolith weights, and in general physical condition as measured by an index of condition of the caudal fin. We suggest that these measures are indicators of stress associated with environmental conditions. Because croaker from different positions along the pollution gradient were distinguishable, it appears that they remain for extended periods within areas of degraded environmental quality.     

Thorn fish Terapon jarbua (Forskål) predation on juvenile white shrimp Penaeus indicus H. Milne Edwards and brown shrimp Metapenaeus monoceros (Fabricius): the effect of turbidity, prey density, substrate type and pneumatophore density

A series of laboratory experiments was conducted at Inhaca Island Marine Biological Station, Mozambique, in order to assess the separate effects of turbidity, prey density, substrate type, pneumatophore density, and the combined effects of turbidity with the latter three, on rate of predation by the thorn fish Terapon jarbua (Forskål, 1775) on white shrimp Penaeus indicus and brown shrimp Metapenaeus monoceros.Significant interactions between turbidity and the other three factors on shrimp predation for both prey species were detected. Regardless of prey density, increasing turbidity decreased predation on P. indicus, but not on M. monoceros, for which increasing densities reduced the protective effect of turbidity. Increasing prey density increased predation on P. indicus in clear water, and increased predation on M. monoceros in low and high, but not in intermediate turbidity or clear water. The presence of a substrate suitable for burying decreased predation on M. monoceros in clear water, but not in the turbidity levels used. In clear water, solely sandy-shell substrate afforded protection to P. indicus, while in turbid water, no substrate offered significant protection and muddy substrate even increased prey vulnerability to fish probably as a result of increased preys' locomotor activity. Raising pneumatophores density seems to lower the protective value of turbidity for both species. In clear water, only low and high structure density provided a deterrent effect on predation on P. indicus; in turbid water, intermediate and higher structure density increased predation. Increasing structural complexity reduced predation on M. monoceros linearly in clear water; but in low turbid water it increased. In high turbid waters, the increase was only significant in intermediate pneumatophore density. High structural complexities impair the pursuing capacity of fish and thus decreased predation rates. The results indicate that the effective provision of shelter of different habitats depends not only on the various environmental parameters analysed, but also on the way they interact and on the behaviour of prey and predator as well.     

The effect of starvation on the ultrastructure of the red and white myotomal muscles of the crucian carp (Carassius carassius)

Summary The effect of 16 weeks total starvation on the ultrastructure of the red and white myotomal muscles of the crucian carp (Carassius Carassius) has been investigated. In the white fibres the amount of myofibrillar material fell from 89.6% to 70.7% of the total fibre volume whilst in the red fibres the fall was from 72.2% to 70.3%. The sarcoplasmic reticulum appeared to have become swollen during starvation in both fibre types. In the white fibres the terminal cisternae of some triads seem to have fused. The volume of the red fibres occupied by mitochondria was reduced from 16.2 % to 5.9 %. The concentration of mitochondria in the white fibres was too low to detect any quantitative changes. A marked reduction in the amount of euchromatin material was observed in most white fibre nuclei and many red fibre nuclei. Many of the ultrastructural changes noted in the present study can be correlated with biochemical changes known to occur in the red and white myotomal muscles of fish during starvation. This work was supported by a grant from the Natural Environmental Research Council.     

Density and maturation of rodlet cells in brain tissue of fathead minnows (Pimephales promelas) exposed to trematode cercariae

Evidence for the presumed linkage between the enigmatic rodlet cells of fish and exposure to helminths is anecdotal and indirect. We evaluated the proliferation and development of rodlet cells in the optic lobes of fathead minnows exposed to cercariae of Ornithodiplostomum ptychocheilus. Mean rodlet cell densities (ca. 10/mm²) in the optic lobes were similar between unexposed controls and minnows with 1- and 2-week old infections. Rodlet cell densities increased at 4 weeks p.i., reaching maxima (ca. 200/mm²) at 6 weeks p.i., followed by a decline at 9 weeks. This temporal pattern of proliferation and maturation paralleled the development of metacercariae within the optic lobes. Unencysted metacercariae develop rapidly within tissues of the optic lobes for approximately 4 weeks after penetration by cercariae, then shift to the adjacent meninges to encyst. The former stage is associated with tissue damage, the latter with massive inflammation of the meninges. Thus, peak densities and maturation of rodlet cells correspond to the period when inflammation of the meninges caused by the large metacercarial cysts is at a maximum. Our results support recent contentions that rodlet cells comprise part of the host inflammatory defence response.     

The Isolation and Characterization of Glycosylated Phosphoproteins from Herring Fish Bones

Past studies of bone extracellular matrix phosphoproteins such as osteopontin and bone sialoprotein have yielded important biological information regarding their role in calcification and the regulation of cellular activity. Most of these studies have been limited to proteins extracted from mammalian and avian vertebrates and nonvertebrates. The present work describes the isolation and purification of two major highly glycosylated and phosphorylated extracellular matrix proteins of 70 and 22 kDa from herring fish bones. The 70-kDa phosphoprotein has some characteristics of osteopontin with respect to amino acid composition and susceptibility to thrombin cleavage. Unlike osteopontin, however, it was found to contain high levels of sialic acid similar to bone sialoprotein. The 22-kDa protein has very different properties such as very high content of phosphoserine (∼270 Ser(P) residues/1000 amino acid residues), Ala, and Asx residues. The N-terminal amino acid sequence analysis of both the 70-kDa (NPIMA(M)ETTS(M)DSKVNPLL) and the 22-kDa (NQDMAMEASSDPEAA) fish phosphoproteins indicate that these unique amino acid sequences are unlike any published in protein databases. An enzyme-linked immunosorbent assay revealed that the 70-kDa phosphoprotein was present principally in bone and in calcified scales, whereas the 22-kDa phosphoprotein was detected only in bone. Immunohistological analysis revealed diffusely positive immunostaining for both the 70- and 22-kDa phosphoproteins throughout the matrix of the bone. Overall, this work adds additional support to the concept that the mechanism of biological calcification has common evolutionary and fundamental bases throughout vertebrate species.     

Plasticity of gonad development in hermaphroditic sparids: ovotestis ontogeny in a protandric species,Lithognathus mormyrus

Synopsis Heterosexual gonad development in a sparid species, Lithognathus mormyrus, was studied by histological and cytological examination, during the first three years of life. Gonad bisexuality is achieved after two months of development, according to the cytological dynamics known in sparids. In one-year-old fishes, a variability in the gonad morphology of the juvenile is shown: three different types of ovotestis have been identified within the same cohort: ovotestes with testicular prevalence (25%), testicular and ovarian equivalence (20%), and ovarian prevalence (55%). This morphological variability of the juvenille ovotestes was consistent with the histological analysis of the sexual structure of the adult stock at the first sexual maturity, which constituted 55.5% of functional males (stemming from the first types of ovotestis) and 44.5% of primary females (from the third type). The plasticity of sexual expression in sparids is emphasized, revealing the potentialities of the ovotestis.     

The effect of a large-scale irrigation scheme on the fish community structure and integrity of a subtropical river system in South Africa

Large scale irrigation schemes are vitally important for food security in developing countries. This is especially relevant in subtropical countries where there is pressure on their water resources. However, the potential impacts on the fish communities of the rivers associated with these irrigation systems are extensive and potentially devastating. Therefore, the aim of the study was to evaluate the impact of the Vaalharts Irrigation Scheme (VHIS) on the fish community of two rivers (Harts and Vaal rivers) in the subtropical region of South Africa. The fish community was assessed during a three year period from 2007 to 2009 together with environmental and habitat quality parameters. A multivariate approach together with a local biotic index was used to determine the present ecological state and the environmental drivers responsible for the fish community structure. The results indicated that the fish community was in a largely natural state at the start of the VHIS and increasingly became modified due to various environmental parameters being affected by the irrigation scheme. Annual variation in the fish community structures was high while nitrate, zinc and sulphates corresponded with changes in the fish community. The outcome of the study highlighted that a lack of long term monitoring of fish community structures together with environmental and habitat parameters are a major challenge in many developing countries that can potentially affect management of irrigation schemes and the fish communities associated with the aquatic ecosystems.     

Multi-species response to rapid environmental change in a large estuary system: A biochronological approach

The sensitivity of species to environmental change is dependent on their ecological requirements (i.e. specialist v. generalist), and hence likely to be species-specific. Identifying species level variation in environmental sensitivity informs assessments of community vulnerability and assists in developing adaptive management strategies. We investigated species-specific sensitivity in fish to understand the vulnerability of differing life histories and ecological requirements to rapid environmental alteration (i.e. drought). Biochronologies of fish growth, based on increment widths in otoliths, were analysed using a mixed modelling approach. We assessed multi-decadal responses in fish growth to environmental variation in the terminal system of Australia’s largest river, for three long-lived fish species with differing life histories and ecological requirements: a freshwater specialist and two estuarine generalists. Biochronologies were between 20 and 38 years long, spanned a decade of severe drought and showed considerable inter-annual variation in growth. Precipitation influenced the growth of the obligate freshwater specialist, Macquaria ambigua ambigua. Temperature and salinity influenced the growth of the two estuarine generalists: Argyrosomus japonicus (estuarine opportunist) and Acanthopagrus butcheri (estuarine dependent), respectively. These results suggest that generalisations about how species respond to environmental change may mask species-specific responses to dependent on the constraints of their ecological requirements (i.e. specialist v. generalist). These findings also highlight the importance of considering the diversity of life history strategies that inhabit an ecosystem when developing conservation and management strategies.     

Early ontogeny of Adinia xenica (Pisces,Cyprinodontiformes): 2. Implications of embryonic resting interval for larval development

Synopsis Larval development commences with first exogenous feeding, and ends with final remodelling of caenogenetic structures into the definitive organs of juvenile and adult. For the intertidal cyprinodontid Adinia xenica this generally corresponds to the interval between hatching and completion of scalation. The final step of the embryo period is a resting interval of variable duration. Embryos were induced to hatch after 2 and 10 days of this near arrest. Although the general pattern of larval development was the same for both groups, differences were observed in the rates and order of calcification of skeletal elements, fin differentiation and growth, and scalation. For example, embryos hatching 8 days later in the resting interval were already pattially calcified, but completed calcification at a slower rate than the group hatching after 2 days. These differences may be due to effects of the duration of the resting interval itself; or they may reflect genetic variation of which age at hatching is only one manifestation.