Bernhard Rennert

Treatment of rainbow trout farm effluents in constructed wetland with emergent plants and subsurface horizontal water flow

The objective of this research was to investigate treatment of aquaculture effluents of flow-through systems in created wetlands. The constructed wetlands types used in this study were subsurface root zone systems with emergent plants and horizontal effluent soil percolation. Three 1.40×1.00×0.70 m (L×W×H) root zone systems were filled with sands of 1–2 mm particle size and planted with 20 rooted shoots of reed per square meter (Phragmites australis). Nutrient removal of rainbow trout (Oncorhynchus mykiss) effluents flowing through the wetland was determined for hydraulic loading rates of 1, 3 and 5 l/min corresponding to very short hydraulic residence times (HRTs) of 7.5, 2.5 and 1.5 h, respectively. Inflowing nutrients were removed within every continuously flooded wetland. Total suspended solids (TSS) and chemical oxygen demand (COD) were reduced by 95.8–97.3% and 64.1–73.8%, respectively, and demonstrated no influence of HRT. Total phosphorus (TP) and total nitrogen (TN) removal rates varied from 49.0% to 68.5% and 20.6% to 41.8%, respectively, and were negatively correlated with HRTs. Effluent purification was best at HRT of 7.5 h, but sufficient removal rates were achieved for shorter HRTs.

Influence of temperature on puberty and maturation of pikeperch, Sander lucioperca

Among external factors, temperature is known to exhibit a prominent role in reproduction of temperate fish species. Here, temperature related induction of puberty in pikeperch Sander lucioperca was investigated. For the first time the key factors of the pikeperch brain-pituitary-gonad axis, targeting the mRNA expression of the luteinising hormone (LH) and the follicle stimulating hormone (FSH), as well as the plasma sex steroids estradiol (E2), testosterone (T), 11-ketotestosteron (11-KT) and 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) were addressed in the experiment. Concomitant the maturational stages were described histologically. After 3 months, female pikeperch kept at 12°C revealed significant increases in the GSI and plasma E2 concentration and 90% of the females were mid-vitellogenic. After 5 months, females kept between 9 and 15°C exhibited significant up-regulation of E2 and GSI as well as comparable histological outcome. At 6 and 23°C in nearly all females stagnation of oogenesis was recorded. Congruently, T was increased at 12 and 15°C. Expression analysis revealed a significant up-regulation of LHβ and FSHβ mRNA in females from early-vitellogenesis, and from mid-spermatogenesis in males, correlated to elevated plasma concentrations of steroids (except for E2 in males). In conclusion, moderate temperatures (12-15°C for) for at least 3 months were required to proceed with first maturation in juvenile pikeperch. The most efficient effect was observed at 12°C, while high (23°C) or low (6°C) temperatures prevented gonadal maturation. So temperature was identified as a prime factor in the induction of puberty in pikeperch, as revealed by histological as well as endocrine parameters.

Impact of microcystin containing diets on physiological performance of Nile tilapia (Oreochromis niloticus) concerning stress and growth

Diets containing Microcystis with considerable amounts of the cyanotoxin microcystin-LR (MC-LR) were fed to determine their impact on the physiological performance of the omnivorous Nile tilapia (Oreochromis niloticus) with regard to stress and growth performance. Four different diets were prepared based on a commercial diet (control, MC-5% [containing 5% dried Microcystis biomass], MC-20% [containing 20% dried Microcystis biomass], and Arthrospira-20% [containing 20% dried Arthrospira sp. biomass without toxin]) and fed to female Nile tilapia. Blood and tissue samples were taken after 1, 7, and 28 d, and MC-LR was quantified in gills, muscle, and liver by using high-performance liquid chromatography (HPLC). Only in the liver were moderate concentrations of MC-LR detected. The stress hormone cortisol and glucose were analyzed from plasma, suggesting that all modified diets caused only minor to moderate stress, which was confirmed by analyses of hepatic glycogen. In addition, the effects of the different diets on growth performance were investigated by determining gene expression of hypophyseal growth hormone (GH) and hepatic insulin-like growth factor-I (IGF-I). For all diets, quantitative reverse transcription-polymerase chain reaction (RT-qPCR) demonstrated no significant effect on gene expression of the major endocrine hormones of the growth axis, whereas classical growth data, including growth and feed conversion ratio, displayed slight inhibitory effects of all modified diets independent of their MC-LR content. However, no significant change was found in condition or hepatosomatic index among the various diets, so it seems feasible that dried cyanobacterial biomass might be even used as a component in fish diet for Nile tilapia, which requires further research in more detail.

The Apparent Nutrient Digestibility of Diets Containing Fish Meal or Isolated Soy Protein in Sterlet (Acipenser ruthenus)

Feeding experiments were conducted to determine the apparent digestibility coefficients (ADCs) for sterlet (Acipenser ruthenus) fed diets containing different protein sources (fish meal and isolated soy protein). The ADCswere measured using the indirect chromic oxide method. The fish were fed at a rate of 1.5% body weight per day. Faecal samples were collected by continuous filtration of the effluent water from the rearing tanks during an 8-week feeding period. The digestibility of protein was significantly higher in the diet containing isolated soy protein (93.63%) than in the diet containing fish meal (89.82%). In contrast, digestibility of lipid and energy were significantly higher in the diet containing fish meal. However, although isolated soy protein was well digested by sterlet, body weight increase and specific growth rate were significantly lower in fish led the isolated soy protein diet than in fish fed the fish meal diet.

Impact of microcystin containing diets on physiological performance of Nile tilapia (Oreochromis niloticus) concerning detoxification.

Nile tilapia (Oreochromis niloticus) were fed by diets supplemented with cyanobacteria containing in part the cyanotoxin microcystin-LR (MC-LR) to determine the potential impacts on detoxification. Four different diets were prepared based on a commercial diet: (1) control, (2) MC-5% (containing 5% dried Microcystis sp. biomass with 4.92 μg MC-LR g(-1) diet), (3) MC-20% (containing 20% dried Microcystis sp. biomass with 19.54 μg MC-LR g(-1) diet), and (4) Arthr-20% (containing 20% dried Arthrospira sp. biomass without MC-LR). Blood and liver samples were taken after one, 7, and 28 days and protein has been determined in plasma and liver. In the liver, impacts on detoxification were measured by glutathione-S-transferase (GST) activities and gene expression of multi drug resistance protein (MDRP). Plasma protein did not change between all four diets at any sampling time whereas liver protein was significantly elevated already after one day in Arthr-20% and after 28 days in both, MC-20% and Arthr-20%. Biochemical measurements of GST activities revealed no significant impact at any sampling time. In order to characterize the potential effect of MC-LR on MDRP, RT-qPCR method was established. However, as for GST activities no significant changes in MDRP gene expression have been observed. Thus, in summary, oral exposure of MC-LR containing cyanobacteria to Nile tilapia via feed ingestion did not impact significantly detoxification in liver concerning GST activities and MDRP expression despite biochemical composition concerning liver protein was significantly elevated by the diets containing 20% cyanobacteria biomass, regardless whether they contained MC-LR or not.