Effects of dietary vitamin B1 (thiamine) and magnesium on the survival, growth and histological indicators in lake trout (Salvelinus namaycush) juveniles.

An interaction of two essential nutrients, thiamine and magnesium (Mg) has been documented in in vitro and in vivo studies in mammalian metabolism. However, the role of this association in poikilothermic vertebrates, such as fish, remains elusive. The purpose of this study was first to investigate the effects of dietary thiamine and Mg, and their interaction in lake trout and second to better understand the mechanism leading to early mortality syndrome (EMS), which is caused by a low thiamine level in embryos of many species of salmonids in the wild. Semi-purified diets (SPD) were prepared to accomplish 2 × 2 factorial design that were either devoid of or supplemented with thiamine mononitrate (20 mg/kg diet), magnesium oxide (700 mg/kg diet), or both. Lake trout alevins at the swim-up stage were fed for 10 wk one of the SPD diets or a commercial diet at the same rate (2.0-1.5%) based on recorded biomass. Our results showed that the concentrations of thiamine in the trunk muscle and Mg of whole body were closely associated with the dietary level of two nutrients. The interaction of low dietary Mg and thiamine resulted in apparently worsened overt symptoms of thiamine deficiency in lake trout leading to a higher mortality of fish during the seven week long trial (P<0.05). The fish fed a thiamine-devoid and Mg-supplemented diet were presumed to survive longer (10 wk) than the fish fed diets devoid of both nutrients (discontinued after 7th wk due to high mortality). However, we did not observe histopathological changes in the brain and liver corresponding to thiamine concentrations in tissues. These data suggest that Mg enhanced utilization of the thiamine remaining in the fish body and its interdependence was consistent with observations in mammals. EMS severity might be worsened when Mg is deficient in parental diets (and consequently in yolk sac) and/or first feed.

Complex innervation patterns of the conus arteriosus in the heart of the longnose gar, Lepisosteus osseus.

Anatomical and functional studies of the autonomic innervation in the conus arteriosus of the garfishes are lacking. This study reveals that the conus arteriosus of the longnose gar is primarily myocardial in nature, but additionally, large numbers of smooth muscle cells are present in the subendocardium. A well-developed system of adrenergic, cholinergic, substance P (SP) and neuronal nitric oxide synthase (nNOS) positive nerve terminals are found in the wall of the conus arteriosus. Coronary blood vessels running in the adventitia receive a rich supply of nNOS positive nerve fibers, thus suggesting their importance in the nitrergic control of blood flow in the conus arteriosus. The present data show that the patterns of autonomic innervation of the garfish conus arteriosus are more complex than previously appreciated.

The nature of exocytosis in the yolk trophoblastic layer of silver arowana (Osteoglossum bicirrhosum) juvenile, the representative of ancient teleost fishes.

We have chosen the silver arowana (Osteoglossum bicirrhosum), a representative of the most ancient teleost family Osteoglossidae, to address the question of yolk nutrients utilization. Silver arowana have particularly large eggs (1-1.5 cm of diameter) and a unique morphology of the yolk. We present evidence that the yolk cytoplasmic zone (ycz) in the "yolksac juveniles" is a very complex structure involved in sequential processes of yolk hydrolysis, lipoprotein particles synthesis, their transport, and exocytosis. Vacuoles filled with yolk granules in different stages of digestion move from the vitellolysis zone through the ycz to be emptied into the microvillar interspace in the process of exocytosis. The area of the ycz with the abundance of the mitochondria must play an important role in providing energy for both the transport of vacuoles and the release of their contents. Therefore, we postulate that the function of yolk syncytial layer (ysl) as the "early embryonic patterning center" transforms in fish larvae or yolksac juveniles into a predominantly specialized role as the yolk trophoblastic layer (ytl) involved in yolk nutrients utilization. In addition to discovering the mechanism of transformation of the ysl function into ytl function, we suggest that the machinery involved in nutrient mobilization and exocytosis in yolk of arowana yolksac juveniles can be very attractive system for studies of regulatory processes in almost all secretory pathways in animal cells.

Effects of vitamin B1 (thiamine) deficiency in lake trout (Salvelinus namaycush) alevins at hatching stage.

The objectives of this study were to examine the relationship between thiamine concentrations in unfertilized eggs and yolksac individuals of lake trout (Salvelinus namaycush), along with any associated histopathological changes in the tissues of alevins at the hatching stage. We address these questions in a lake trout population from different spawning grounds of Lake Michigan (North and South), known for compromised survival due to early mortality syndrome (EMS). However, a dichotomous forage base of lake trout spawning stocks, with a dietary thiaminase-rich alewife in the North, and dietary low-thiaminase round goby in the South, provides the basis for the assumption that different diets may lead to differences in severity of EMS between different stocks. Lake trout eggs of 18 females were collected and fertilized individually with the sperm of several males. The eggs, eyed embryos and newly-hatched alevins were sampled to examine thiamine utilization during embryogenesis. Progenies of females with low (< 0.73 nmol/g) and high (> 0.85 nmol/g) levels of thiamine were chosen for histological studies. The obtained results showed that total thiamine levels in the body and yolk of eyed embryos and alevins at hatching were influenced by thiamine levels of unfertilized eggs and it decreased during embryogenesis (to 51% in eyed embryos and 28% in newly-hatched alevins in comparison to unfertilized eggs). The survival of lake trout until hatching stage does not correlate with the thiamine level, however it was affected by collection site and was significantly higher in fish from the South site (Julian's Reef). At the hatching stage, no pathological changes were observed in the brain, olfactory lobe, retina or liver in embryos regardless of thiamine concentrations in unfertilized eggs. It has been concluded that an enhanced thiamine requirement for the fast muscle mass growth near the swim-up stage is responsible for overt and histopathological signs of EMS. Current study confirms earlier findings that lake trout suffering from EMS can be successfully treated by immersion in thiamine solution as late as at the swim-up stage.

Effects of vitamin B1 (thiamine) deficiency in lake trout alevins and preventive treatments.

The objectives of this study were to examine the effect of thiamine immersion of fish from a population known for compromised survival as a result of early mortality syndrome (EMS) and to investigate the cause-response relationship between thiamine concentration and lesions in tissues in swim-up-stage lake trout Salvelinus namaycush alevins. Lake trout eggs from 14 fish from Lake Michigan were artificially fertilized and the progeny divided into two groups based on the thiamine concentration (low [< 0.73 nmol/g] or high [> 0.85 nmol/g]) in the unfertilized eggs. Progeny were treated or not with a thiamine solution (2,000 mg/L for 2 h) at hatching or the swim-up stage. The survival of progeny in control groups at the swim-up stage correlated with thiamine concentration. The low thiamine-treated groups had significantly higher survival between the swim-up stage (812.0 degree-days) and 16 d after swim-up (963.3 degree-days) than the control groups; the survival of the high thiamine-treated groups did not differ between treated and control fish, regardless of the treatment at hatching and the swim-up stage. Control alevins that had low thiamine levels showed EMS, which resulted in 94.9-100% mortality 16 d after the swim-up stage. No pathological changes were observed in the brain, olfactory lobe, eye, liver, or muscle in alevins of high thiamine-treated group. Glycogen deposits in the liver of alevins from the low control group were variable, no glycogen being observed in the hepatocytes of 7 of the 24 fish. We demonstrate that thiamine treatment at swim-up enhances the survival of EMS-affected lake trout relative to treatment at hatching.