Pubertal development of male African catfish,Clarias gariepinus. In vitro steroidogenesis by testis and interrenal tissue and plasma levels of sexual steroids

In fish, sex steroids initiate and/or accelerate the maturation of the brain-pituitary-gonad axis. In order to obtain information on the steroid milieu during the pubertal development of male African catfish, we have monitored the conversion of [³H]-pregnenolone and [³H]-androstenedione by testis and [³H]-pregnenolone by interrenal tissue fragmentsin vitro. Pubertal development occurs between two and six months of age. Testicular development proceeds through four main stages that are characterised histologically by the presence of spermatogonia (stage I), spermatogonia and spermatocytes (stage II), spermatogonia, spermatocytes and spermatids (stage III), and all germ cells including spermatozoa (stage IV). 11β-Hydroxyandrostenedione and cortisol were the main products of testes and interrenal tissue, respectively, in all stages of the pubertal development; a change in the steroidogenic pattern was not observed during this period. The interrenal tissue displayed no significant conversion of [³H]-pregnenolone to 11-oxygenated androgens. Blood plasma was analyzed for the presence of five androgens; testosterone, 11β-hydroxytestosterone, 11β-hydroxyandrostenedione, androstenetrione, and 11-ketotestosterone. 11-Ketotestosterone was the quantitatively dominating androgen in the circulation at all stages of development, which was more pronounced in stages III and IV. The obvious differences between thein vitro andin vivo results, namely 11β-hydroxyandrostenedione being the main testicular productvs. 11-ketotestosterone dominating in the blood, may indicate that 11β-hydroxyandrostenedione is converted to 11-ketotestosterone at extratesticular sites.     

The effects of temperature on sex differentiation and growth of black sea bass (Centropristis striata L.)

To examine the effects of temperature on sex differentiation in the black sea bass ( Centropristis striata L.), a protogynous hermaphrodite, juveniles (∼0.5 g) were cultured in recirculating systems at 17, 21 or 25 °C. Growth was assessed at 155, 182, 241 and 275 days post hatch and sex differentiation was determined histologically. No differences were found in the sex ratios of fish reared at different temperatures, but only 55–64% developed as females. Growth was significantly greater in males across all temperature treatments. These results suggest that black sea bass exhibit sexually dimorphic growth patterns and that female-specific sex determination can be disrupted in culture.     

Protein markers of Marteilia sydneyi infection in Sydney rock oysters, Saccostrea glomerata

Marteilia sydneyi is the causative agent of QX disease in Sydney rock oyster, Saccostrea glomerata . It is responsible for disease outbreaks among oysters that occur during summer and can result in up to 95% mortality. QX disease has significantly decreased S. glomerata production in some areas of Australia's eastern seaboard over the past 30 years. Marteilia sydneyi sporulates in the digestive gland of oysters leading to complete disorganization of the infected tissues. The current study used proteomics to identify potential molecular markers of sporulating M. sydneyi infection during a field trial undertaken in the Georges River, Sydney, between December 2006 and May 2007. Early stages of M. sydneyi infection were detected by polymerase chain reaction, whilst cytological examination was used to identify sporulating M. sydneyi in the gut. Protein expression in oyster haemolymph was assessed during the M. sydneyi infection period by two dimensional electrophoresis. Proteome maps identified significant differences in the expression of four proteins in oysters with sporulating M. sydneyi infections.     

Evaluation of AQUI-STM (efficacy and minimum toxic concentration) as a fish anaesthetic/sedative for public aquaculture in the United States

A preliminary evaluation of efficacy and minimum toxic concentration of AQUI-S^TM, a fish anaesthetic/sedative, was determined in two size classes of six species of fish important to US public aquaculture (bluegill, channel catfish, lake trout, rainbow trout, walleye and yellow perch). In addition, efficacy and minimum toxic concentration were determined in juvenile–young adult (fish aged 1 year or older) rainbow trout acclimated to water at 7°C, 12°C and 17°C. Testing concentrations were based on determinations made with range-finding studies for both efficacy and minimum toxic concentration. Most of the tested juvenile–young adult fish species were induced in 3 min or less at a nominal AQUI-S^TM concentration of 20 mg L^–1. In juvenile–young adult fish, the minimum toxic concentration was at least 2.5 times the selected efficacious concentration. Three out of five species of fry–fingerlings (1.25–12.5 cm in length and < 1 year old) were induced in ≤ 4.1 min at a nominal concentration of 20 mg L^–1 AQUI-S^TM, with the other two species requiring nominal concentrations of 25 and 35 mg L^–1 for similar times of induction. Recovery times were ≤ 7.3 min for all species in the two size classes. In fry–fingerlings, the minimum toxic concentration was at least 1.4 times the selected efficacious concentration. There appeared to be little relationship between size of fish and concentrations or times to induction, recovery times and minimum toxic concentration. The times required for induction and for recovery were increased in rainbow trout as the acclimation temperature was reduced.     

In vitro interactions between Neoparamoeba sp. and Atlantic salmon epithelial cells

Neoparamoeba sp., including the putative aetiological agent of amoebic gill disease in cultured fish (N. pemaquidensis), were incubated in vitro with an Atlantic salmon gill epithelium (RGE-2) cell line. Proliferation by the amoeba population was dependent upon culture osmolarity; no growth occurred at 330 mm x kg(-1) but a sixfold increase was observed at 1000 mm x kg(-1). At 780 mm x kg(-1) there was a fourfold increase in the amoeba population but a concurrent decrease in RGE-2 cell density that was significantly greater than that caused by the high culture osmolarity alone. This apparent cytopathic effect (CPE) developed rapidly and resulted in complete cytolysis of the monolayer in 5 days. CPE occurred in multiple foci and presented as cell vacuolation, rounding and clumping, and the rapid clearance of large areas of the cell monolayer. The possibility that CPE is because of the presence of Neoparamoeba sp. derived cytolytic products is discussed in the context of the pathology of the disease in vivo and the occurrence of secreted cytopathogenic compounds in other amoeba species.     

Demonstration of alternative feeds for the Pacific white shrimp, Litopenaeus vannamei, reared in low salinity waters of west Alabama

The replacement of marine proteins with vegetable proteins or terrestrial animal byproducts in aquaculture diets has been gaining momentum. This study examines the viability of replacing fish meal in shrimp production diets with alternative protein sources (combinations of vegetable proteins) in inland low salinity waters of west Alabama. The test diets were formulated to contain 36% protein and 8% lipid. The basal diet contained 10% fish meal. The fish meal was then replaced (on a weight to weight basis) with poultry meal (PM), pea meal or distiller's dried grain with solubles (DDGS). Two separate experiments (laboratory trial and farm trial) were devised to test the efficacy of the diets for Litopenaeus vannamei reared in low salinity waters. The laboratory trial was conducted at the E. W. Shell Fisheries Research Station in Auburn, Alabama, USA, whereas the farm trial examined the same diets in an outdoor flow-through system at a low salinity shrimp farm in west Alabama. Results indicate no significant differences in shrimp growth, weight gain, survival or feed conversion ratio among dietary treatments, suggesting that PM, pea meal and DDGS can serve as alternatives to fish meal as a protein source for shrimp reared in low salinity environments.     

Diseases of north European wrasse (Labridae) and possible interactions with cohabited farmed salmon, Salmo salar L

There have been several reported studies of wrasse health but none of these has shown transmission of wrasse diseases when stocked with farmed Atlantic salmon. Most of the studies have focussed on bacterial and parasite issues, including treatment of bacterial diseases with antibiotics and vaccination of wrasse. Classical and atypical furunculosis have been reported in wrasse following stress, and wrasse have been susceptible to vibrio infection. Further study is required on the vaccination of wrasse for furunculosis with latent carrier status to maximize survival. There are studies on viral diseases such as infectious pancreatic necrosis, infectious salmon anaemia and pancreas disease and although these did not give any undue concern for salmon health, there is also scope for further study in this area. Resident parasite communities of wrasse are largely host-specific and do not appear to be a threat to salmon. Given that wrasse have not, to date, been a vector of disease in salmon, attention should be placed on maintaining best practice in cohabiting wrasse with salmon. Other issues that should be addressed are good welfare of wrasse in pens and identifying measures of this, the identification of losses of wrasse in pens, being alert to potential emerging diseases through health screening of mortalities and assessing the risks associated with carrying forward wrasse from one salmon production cycle to the next. Issues of exploitation by fishing on wild wrasse stocks and improved biosecurity may be addressed by the increased movement by the industry to the stocking of farmed wrasse.     

Gastric dilation and air sacculitis in farmed chinook salmon, Oncorhynchus tshawytscha (Walbaum)

A syndrome affecting cultured chinook salmon, Oncorhynchus tshawytscha (Walbaum), characterized by distended abdomens, gastric dilation, air sacculitis (GDAS), increased feed conversion rates and increased mortality has been recognized in New Zealand. Affected fish were most obvious in sea cages but were also present in fresh water. Mortality rates associated with this condition were highest in late summer and approached 6% per month. A dilated and flaccid stomach, without visible rugal folds containing copious oil, watery fluid or undigested feed was typical. Gastric mucosal ulceration or inflammation were not present. The air sacculitis consisted of a thickened, dilated bladder with a mixed mucosal inflammatory infiltrate and a luminal exudate associated with large numbers of morphologically diverse bacteria. Gastric dilation or air sacculitis occurred alone or together in the same fish. In a group of 20 subclinically affected fish with or without gastric dilation, there were no significant differences in weight, length, serum osmolality, sodium, total protein or packed cell volume. Twenty-three severely affected fish had significantly ( P  < 0.05) higher serum osmolality but similar sodium and total protein to that of clinically normal fish.     

Climate variability and marine survival of coho salmon (Oncorhynchus kisutch) in the Oregon production area

Time series of adult recruitment for natural runs of coho salmon from the Oregon coastal region (1970–94) and marine survival of hatchery-reared coho salmon from California to Washington (1960–94) are significantly correlated with a suite of meteorological and oceanographic variables related to the biological productivity of the local coastal region. These variables include strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly stratified mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to define the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity. Multiple regression analysis suggests that coho marine survival is significantly and independently related to the dominant modes acting over this region in the periods when the coho first enter the ocean and during the overwintering/spring period prior to their spawning migration. Linear relationships provided good fits to the data and were robust, capable of predicting randomly removed portions of the data set.