Biocomplexity in a highly migratory pelagic marine fish, Atlantic herring

The existence of biologically differentiated populations has been credited with a major role in conferring sustainability and in buffering overall productivity of anadromous fish population complexes where evidence for spatial structure is uncontroversial. Here, we describe evidence of correlated genetic and life history (spawning season linked to spawning location) differentiation in an abundant and highly migratory pelagic fish, Atlantic herring, Clupea harengus, in the North Sea (NS) and adjacent areas. The existence of genetically and phenotypically diverse stocks in this region despite intense seasonal mixing strongly implicates natal homing in this species. Based on information from genetic markers and otolith morphology, we estimate the proportional contribution by NS, Skagerrak (SKG) and Kattegat and western Baltic (WBS) fish to mixed aggregations targeted by the NS fishery. We use these estimates to identify spatial and temporal differences in life history (migratory behaviour) and habitat use among genetically differentiated migratory populations that mix seasonally. Our study suggests the existence of more complex patterns of intraspecific diversity than was previously recognized. Sustainability may be compromised if such complex patterns are reduced through generalized management (e.g. area closures) that overlooks population differences in spatial use throughout the life cycle.     

A survey of red and white muscle in marine fish

The proportion of the mytomal muscle that comprises red or slow muscle fibres was assessed histologically for 84 species of marine fish. The results are discussed in relation to their mode of life.     

Free and membrane-bound lactate dehydrogenase from white driving muscles of skate.

Purified cytoplasmic and membrane-bound lactate dehydrogenases (LDH) from white muscle of skate were characterized, Km for pyruvate and NADH for purified LDH were 150 +/- 16 and 29 +/- 7 microM, and for membrane-bound LDH were 185 +/- 22 and 7.5 +/- 1.5 microM, respectively. The membrane-bound enzyme was not inhibited by high pyruvate concentration (up to 20 mM) in contrast to purified LDH. Part of membrane-bound LDH was released by incubation in solutions with a high level of KCl (up to 1 M) or at alkaline pH. The inactivation rate during trypsin digestion for solubilized LDH was 2-3-fold higher than that for the membrane-bound enzyme.     

Pentose phosphate pathway and nucleic acid metabolism in red and white muscles of fish

The activities of the pentose phosphate cycle enzymes, the content of nucleic acids and the activities of acid and alkaline RNAses in the heart and red and white muscles of cartilaginous and teleost fish were determined. It was found that the rates of the dehydrogenase and transferase reactions of the pentose phosphate pathway and the nucleic acid metabolism in the red muscles and heart are much higher than those in the white muscles of the species under study.     

Free amino compounds and cell volume regulation in erythrocytes from different marine fish species under hypoosmotic conditions: the role of a taurine channel

Erythrocytes from the marine fish species ballan wrasse (Labrus berggylta Ascanius), bullhead (Myoxocephalus scorpius L.), cod (Gadus morhua L.), dab (Limanda limanda L.), eelpout (Zoarces viviparus L.), flounder (Platichthys flesus L.), lumpfish (Cyclopterus lumpus L.), plaice (Pleuronectes platessa L.), sole (Solea solea L.) and turbot (Scophthalmus maxima L.) possess the capacity for regulatory volume decrease. This property was demonstrated in vitro by reduction of the osmolality of the incubation medium from 330 to 255 mosmol·kg^-1. During the 4-h incubation period only the lumpfish cells completely regained the original volume. Twenty-seven free amino compounds were present in detectable amounts in the erythrocytes. At normal osmolality the taurine content was between 14.0 mol·g dry weight^-1 (lumpfish) and 147.4 mol·g dry weight^-1 (sole). Except in the bullhead, taurine was the quantitatively dominating amino compound in the erythrocytes from all species, and accounted for betwee 23% (lumpfish) and 88% (sole) of the total content of free amino compounds. In each species the regulatory volume decrease was associated with a reduction in the cellular content of taurine. Taurine contributed to between 6% (lumpfish) and 36% (flounder) of the cell shrinkage. There was a significant negative correlation, however, between the cellular concentration of taurine at normal osmolality and the capacity of the cells for regulatory volume decrease. Gamma-aminobutyric acid and/or glycine also contributed to the process of volume regulation, but to a lesser extent than taurine. The volume regulatory efflux of taurine and -aminobutyric acid were mediated by taurine channels. It is suggested that these channels also mediated the reduction in the cellular contents of glycine.Abbreviations cmp counts per minute - dw dry weight - GABA -amino-n-butyric acid - MW molecular weight - SD standard deviation - ww wet weight     

Nitrogen pollution in mariculture: toxicity and excretion of nitrogenous compounds by marine fish

Summary The toxicological and environmental significance of N-containing effluents discharged to seawater from fish farms is difficult to establish. Environmental quality standards for N compounds in seawater are hard to derive in the context of aquaculture because the toxicity of NH₃ and NO₂ ^- to marine fish is poorly understood. Furthermore, details of aquacultural effluents are not routinely reported. Marine teleosts excrete N via the gills, skin and faeces, but do not have the metabolic capacity to cause breaches in discharge consent conditions. The most likely cause of discharge consent breaches will be poor farming practice. Nitrogen pollution will arise from food wastage, poor N absorption, and N retention. It is estimated that 52–95% of any N added to the culture system as food will ultimately pollute the environment.     

Cryopreservation of sperm in Brazilian migratory fish conservation

Simple, effective protocols for cryopreserving milt of five Brazilian migratory characids ( Brycon orbignyanus , Prochilodus lineatus , Piaractus mesopotamicus , Salminus maxillosus and Leporinus elongatus ) and one Brazilian migratory catfish ( Pseudoplatystoma corruscans ) are described. Milt was frozen and stored in dry shippers immediately after collection, making the procedure practical for use in the field. A diluent of 5% glucose, 10% dimethyl sulphoxide and 10% egg yolk was effective for all of the characid species, and a diluent of 10% methanol and 15% powdered milk was effective for P. corruscans . Milt was thawed in an ambient temperature water bath (28–30° C). Activation of thawed milt was effective with either saline (0·9 or 0·45% NaCl) or bicarbonate (1% NaHCO₃). Fertilization rates with frozen milt varied between 49 and 300% of the control. Application of the technology for increasing genetic diversity in hatchery programmes for enhancement, mitigation or conservation breeding is discussed, as is its application in aquaculture. Inappropriate use of the technology can threaten wild biodiversity and appropriate legislation and education may be required for its responsible use.     

Mutagenicity testing of imidazole and related compounds.

Ames tests have been performed with imidazole and its principal metabolites, hydantoin and hydantoic acid. N-Acetyl-imidazole, a potential metabolite resulting from the action of intestinal bacteria, and histamine, a structurally related compound which is widely distributed in mammalian tissues, have also been tested. Imidazole and histamine were also tested in the UDS assay in primary rat hepatocytes, while imidazole alone was tested in the M2-C3H mouse fibroblast malignant transformation assay. Imidazole gave consistently negative results in the Ames test, the UDS assay and the transformation assay. The three metabolites of imidazole, namely hydantoin, hydantoic acid and N-acetyl-imidazole, all gave negative results in the Ames test. Histamine gave no evidence of mutagenic activity in the Ames test or of genotoxicity in the UDS assay. These results indicate that imidazole and its metabolites are unlikely to present a mutagenic or carcinogenic hazard.     

Overdispersion in marine fish parasites

A modification of Taylor's Power law was used to compare the degree of overdispersion in frequency distributions from 38 datasets of marine parasites, data that had originally been collected for fish stock discrimination. The results strongly indicate that the overriding factor contributing to overdispersion in these helminths and crustaceans is the number of hosts in the life cycle. This was particularly well shown by juveniles of Anisakis 1 from different fish species. Data on the cestode Otobothrium cysticum and the monogenean Pricea multae appear anomalous and lead to conclusions about their biology not at first evident from the literature.