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The ultrastructural pathology in liver, brain, skeletal and cardiac muscle of Baltic salmon yolk sac fry with the M74 syndrome is described. In the clinical stage of disease, the main pathological findings in the liver were a depletion of glycogen, condensation of nuclear chromatin, hydropic degeneration of mitochondria and a dilation of the bile canaliculi. In the terminal stage, additional findings were lipid accumulation and myelin whorls in the cytoplasm. The rough endoplasmic reticulum (RER) was degranulated and vesiculated and in some individuals, it formed concentric membranous whorls. Mitochondria showed several additional lesions, such as matrix densities, pleomorphism and cristae abnormalities. Skeletal myocytes were degenerated, and intracellular lipid accumulation was seen in the myocardium. In the brain, an increased frequency of cells exhibiting pyknosis or karryorhexis was recorded. The cytoplasm of these cells formed an amorphous mass of moderate density. The evaluation of brain and skeletal muscle was complicated by sporadic occurrence of pathological findings in the reference material, i.e. clinically healthy Baltic salmon yolk sac fry. As these yolk sac fry are suspected to have a subclinical thiamine deficiency, reference material in future studies should include salmon yolk sac fry from Atlantic populations or originating from reared broodstock. [ABSTRACT FROM AUTHOR]

Many wildlife populations are declining at rates higher than can be explained by known threats to biodiversity. Recently, thiamine (vitamin B 1 ) deficiency has emerged as a possible contributing cause. Here, thiamine status was systematically investigated in three animal classes: bivalves, ray-finned fishes, and birds. Thiamine diphosphate is required as a cofactor in at least five life-sustaining enzymes that are required for basic cellular metabolism. Analysis of different phosphorylated forms of thiamine, as well as of activities and amount of holoenzyme and apoenzyme forms of thiamine-dependent enzymes, revealed episodically occurring thiamine deficiency in all three animal classes. These biochemical effects were also linked to secondary effects on growth, condition, liver size, blood chemistry and composition, histopathology, swimming behaviour and endurance, parasite infestation, and reproduction. It is unlikely that the thiamine deficiency is caused by impaired phosphorylation within the cells. Rather, the results point towards insufficient amounts of thiamine in the food. By investigating a large geographic area, by extending the focus from lethal to sublethal thiamine deficiency, and by linking biochemical alterations to secondary effects, we demonstrate that the problem of thiamine deficiency is considerably more widespread and severe than previously reported.

Sea-run Baltic salmon (Salmo salar) populations are suffering from the M74 syndrome, a reproduction disorder affecting both broodfish and their progeny. The syndrome is usually manifested during the middle part of the yolk-sac fry stage and has been shown to be associated with a thiamine (vitamin B(1)) deficiency. Development of the disease is reversible by thiamine treatments of broodfish or progeny. This study aimed at investigating the ability of the thiamine antagonist pyrithiamine, administered by microinjections 3 days after hatch, to cause M74-like signs i.e. typical clinical symptoms, high mortality rates and histopathological changes. Furthermore, the effects of pyrithiamine on hepatic activities of the thiamine-dependent enzyme transketolase (TK), the glucose-6-phosphate dehydrogenase (G6PDH) and the cytochrome P4501A (CYP1A) were evaluated. Six family groups with differing thiamine status were sampled on three occasions during the yolk-sac fry stage. All pyrithiamine exposed groups, with the exception of the one with the highest thiamine concentration, showed M74-like symptoms and suffered from high mortality. Enzyme activities were not different in pyrithiamine groups as compared with controls. However, the TK-activities were strongly associated with the thiamine concentrations. The G6PDH-activity demonstrated small variations with the highest activities in the M74-groups. The [TK]/[G6PDH]-ratios were considerably lower in the M74-groups than in the healthy controls, indicating an imbalance between the oxidative and the non-oxidative part of the pentose-phosphate shunt due to a deficit in thiamine. The pyrithiamine-injections induced several M74-like symptoms including incoordination, lethargy, whitened liver and yolk-sac precipitates. They also caused high mortality rates, in addition to lowered glycogen levels and increased prevalence of necrotic brain cells. Moreover, the study demonstrates that the TK, G6PDH and CYP1A-activities are associated with the thiamine content., (Copyright 2002 Elsevier Science B.V.)

Sea-run Baltic salmon (Salmo salar) populations have been affected by the M74 syndrome since 1974 causing high yolk-sac fry losses in Swedish compensatory rearing plants. M74 has been shown to be a maternally transmitted thiamine (vitamin B(1)) deficiency. The aim of this study was to investigate possible relationships between thiamine and hepatic activities of the thiamine-dependent enzymes transketolase (TK) and alpha-ketoglutarate dehydrogenase (alpha-KGDH) in addition to glucose-6-phosphate dehydrogenase (G6PDH) and cytochrome P4501A (CYP1A), measured as 7-ethoxyresorufin O-deethylase (EROD), in Baltic salmon yolk-sac fry after treatment with thiamine. Thiamine concentrations and activities of TK, alpha-KGDH and EROD were significantly lower (P<0.05) in M74 groups compared to controls (not developing M74) and family groups of thiamine injected females. In M74-developing groups the thiamine immersions reduced the mortality from 86 to 13% and restored thiamine concentrations and activities of TK, alpha-KGDH and EROD to levels slightly lower than the immersed controls. An interesting fact was that the controls showed significantly elevated (P<0.05) TK and alpha-KGDH-activities after immersions in thiamine, indicating that they also may have a stressed thiamine metabolism. The TK and alpha-KGDH-activities of unimmersed groups correlated significantly (P<0.05) with the thiamine content. We suggest that the low activities of TK and alpha-KGDH in M74 groups may be an integrative part in the pathogenesis of M74 development.

The redox substrates--lactate, malate, alpha-glycerophosphate, dihydroxy acetonephosphate and pyruvate--have been determined in liver and muscle tissue from young salmon. The redox quotients have also been calculated. The freeze clamping technique was used and reliable samples of fish muscle for the determination of lactate were obtained with the aid of a pair of pliers with a gear mechanism. It was established that the lactate content in the body muscle is in close agreement with that in the blood from rested salmon parr. The concentrations of redox substrates are in good agreement with those found in mammalian tissue. The determination of the content of glycogen in fish muscle is discussed in the light of the results obtained in this study.