Habitat use by an endangered riverine fish and implications for species protection

We investigated habitat specificity of the amber darter (Percina antesella Williams & Etnier 1977), an imperiled fish from restricted portions of 2 rivers in the southeastern United States. Foraging amber darters occupied a narrow range of riffle habitat, consistently avoiding areas < 20 cm deep and with velocity < 10 cm. s^?1 near the substrate, occupying areas with cobble or gravel substrate and average water-column velocity of 30 to 70 cm. s^?1. During low to mo'derate flows, approximately 20% or more of the study areas contained suitable habitat for the species. Amber darters appeared rare, and the numbers of individuals were uncorrelated with the concurrent availability of suitable habitat. Protecting the amber darter may require more than maintaining adequate depths and velocities over gravel-cobble substrates. Until we understand the potential importance of migration and dispersal for maintaining small populations, suitable habitat should be maintained over the longest contiguous stream segments possible.     

Microhabitat use, movements and abundance of gilt darters (Percina evides) in southern Appalachian (USA) streams

Abstract –  We examined microhabitat use by gilt darters ( Percina evides ) in two streams in the south-eastern USA. Darters were over-represented in erosional microhabitats with higher average velocities and more cobble. Male darters tended to show stronger selection than females. Size-based analyses showed that larger (≥60 mm) gilt darters tended to use microhabitats with more heterogeneous substrata and more boulder than smaller (≤59 mm) darters. We also conducted a short-term movement study and calculated population estimates based on mark–recapture data in autumn 2005. Darters moved both long and short distances with 40% of all recaptures occurring within 5 m of the initial capture point. Using Program mark and model-averaged parameter estimates gilt darter density was 0.31 darters·m⁻² (225 darters/730 m²). Conservation of this species will require the preservation of erosional habitats in streams.     

The swimming capacity of juvenile Murray cod (Maccullochella peelii): an ambush predator endemic to the Murray‐Darling Basin,Australia

This study documented the swimming capacity of a large ambush predator, Murray cod Maccullochella peelii, endemic to the Murray‐Darling Basin, Australia. It was evident that the species is a swimming generalist, maintaining moderate ability across all aspects of the swimming capacity parameters that were investigated. For instance, the species was capable of prolonged swimming performance (critical swimming speed, U_crit: absolute, 0.26–0.60 m·s^?1, relative, 1.15–2.20 BL s^?1) that was inferior to active fish species, but comparable with other ambush predators. The species had low energetic demands, maintaining a low mass‐specific standard (21.3–140.3 mg·h^?1 kg^?1) and maximum active metabolic rate (75.5–563.8 mg·h^?1 kg^?1), which lead to a small scope for activity (maximum active metabolic rate–standard metabolic rate; 1.4–5.9). They were reasonably efficient swimmers (absolute and relative optimal swimming speed, 0.17–0.61 m·s^?1 and 0.77–1.93 BL·s^?1, respectively) and capable of repeat bouts of prolonged performance (recovery ratio = 0.99). Allometric changes in aspects of swimming capacity were realised with body mass, whereas broad swimming capacity was maintained across a wide range of temperatures. The swimming capacity demonstrated by M. peelii reflects a sit‐and‐wait foraging strategy that seeks to conserve energy characteristic of ambush predators, but with distinct features (e.g., lack of fast‐start ability) that may reflect their evolution in some of the world's most hydrologically and thermally variable rivers.     

Aeration rate adjustment at night to prevent sinking syndrome‐related death in the tiger grouper Epinephelus fuscoguttatus (Perciformes:Serranidae) larvae

The effects of different aeration rates at night to prevent sinking syndrome‐related death (SSRD) of the tiger grouper, Epinephelus fuscoguttatus were examined. The aeration rates were fixed at 300 mL min^?1 at daytime (07:00–19:00 hours) and regulated to 0, 300 and 900 mL min^?1 at night (19:00–07:00 hours). Larval survival, growth, feeding intake, sinking velocity, distribution and behaviour, stress level, surface tension‐related death (STRD) and flow velocity distribution were assessed. The occurrence of SSRD in the tiger grouper was observed through the accelerated sinking velocity (Vl) (from 0.15 ± 0.09 cm s^?1 at 4 days AH to 0.41 ± 0.09 cm s^?1 at 12 days AH) coupled with larval passive swimming behaviour at night‐time. On the final day of experiment (15 days AH), larvae reared in 900 mL min^?1 at night had attained significantly higher (P < 0.05) survival (34.4 ± 5.5%), growth (5.8 ± 0.5 mm) and feeding intake (60.46 ± 6.98 ind. larva^?1). A favourable flow field for the tiger grouper was produced in 900 mL min^?1 at night‐time, in which larvae were transported 15–25 cm above the tank bottom and 1.0 cm beneath the water surface. Under these night‐time rearing conditions, larval stress level and number of STRD reared in 900 mL min^?1 compared with those observed in 300 mL min^?1 remained insignificant, indicating that strong turbulence of flow velocity was not detrimental for larvae. Our findings recommend aeration at 900 mL min^?1 at night as this could improve larval survival by reducing SSRD.     

Sex differences in metabolic rate and swimming performance in pink salmon (Oncorhynchus gorbuscha): the effect of male secondary sexual traits

Do secondary sexual traits, such as large dorsal hump and hooked snout, decrease the swimming efficiency of male pink salmon during freshwater migration? This is the first study to address the effects of secondary sexual traits in pink salmon on oxygen uptake and swimming capacity. We conducted a laboratory experiment using a swimming respirometer and a field study using electromyogram (EMG) telemetry in the Shibetsu River, Hokkaido, Japan. We compared the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1) in male and female fish, and also investigated the effects of morphological traits (secondary sexual characters) on the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1). Additionally, we compared energy costs and swimming behaviour during upstream migration between male and female pink salmon. The laboratory experiment revealed that MO₂ exponentially increased with increasing U; this increase was described by MO₂ = 167.9e^1.23U for males and 144.9e^1.14U for females. Linear mixed models found that hump height and the upper jaw length in males significantly and positively affected the relationship between MO₂ and U; no effect was found in females. The field study found that swimming velocity for both sexes estimated from EMG calibration was lower than optimal swimming velocity (U_opt) calculated from the laboratory experiment. We suggest that pink salmon in the Shibetsu River do not swim at the optimal swimming velocity because of the short migration distance involved (20 km).     

Behaviour and physiology of mountain whitefish ( Prosopium williamsoni) relative to short‐term changes in river flow

Despite the growing recognition that river flow can have an effect on the growth, distribution and survival of fishes, little is known about the underlying mechanisms to explain this effect. Furthermore, there are few examples of integrated measures of behaviour and physiology to study the responses of fish to river hydrology. Here, axial swimming muscle electromyograms were logged as a sensitive indicator of activity from 19 mountain whitefish ( Prosopium williamsoni) across a large range of hourly discharge magnitudes (mean = 621 m³·s^?1, range = 0–1770 m³·s^?1) in a hydropeaking reach of the Columbia River, Canada. Hourly mean discharge had a significant positive effect on swimming muscle activity. However, a large amount of the variance was unexplained, possibly due to social interactions, feeding and/or flow‐refuging behaviours. Fluctuating flows were no more energetically costly than stable flows. Discharge magnitude had a significant positive effect on blood cortisol concentrations. Yet, cortisol concentrations were low overall (mean ± SD = 1.60 ± 0.09 ng·ml^?1), suggesting that the small observed response could be the result of routine physiological processes rather than a stress response per se. Based on low blood lactate concentrations, mountain whitefish were not swimming exhaustively (i.e., anaerobic burst‐type swimming) at high flows.     

Movements and habitat use of common carp (Cyprinus carpio) and Murray cod (Maccullochella peelii peelii) juveniles in a large lowland Australian river

Abstract – Native Murray cod (Maccullochella peelii peelii) are listed as a nationally vulnerable species, whereas non‐native common carp (Cyprinus carpio) are widespread and abundant. Understanding key aspects of life history, such as movement patterns and habitat selection by juvenile Murray cod and common carp, might be useful for conserving Murray cod populations and controlling common carp numbers. We used radio‐telemetry to track eight juvenile Murray cod and seven juvenile common carp in the Murray River, Australia, between March and July 2001. Common carp occupied a significantly greater total linear range (mean ± SD: 1721 ± 1118 m) than Murray cod (mean ± SD: 318 ± 345 m) and the average daily movement was significantly greater for common carp (mean ± SD: 147 ± 238 m) than for Murray cod (mean ± SD: 15 ± 55 m). All Murray cod and five of the seven common carp displayed site fidelity or residency to one, two or three locations. Murray cod were found only in the mainstream Murray River among submerged woody habitats, whereas common carp occurred equally in mainstream and offstream areas, and among submerged wood and aquatic vegetation. Murray cod were found in deeper (mean ± SD: 2.3 ± 0.78 m) and faster waters (mean ± SD: 0.56 ± 0.25 m·s^?1) compared with common carp (mean ± SD: 1 ± 0.54 m; 0.08 ± 0.09 m·s^?1) respectively. The presence of juvenile Murray cod only amongst submerged wood is an indication that these habitats are important and should be preserved. Conversely, juvenile common carp were equally present among all habitats sampled, suggesting that habitat selection is less specific, possibly contributing to their widespread success.     

Summer microhabitat use by adult and young‐of‐year snail darters (Percina tanasi) in two rivers

Ashton MJ, Layzer JB. Summer microhabitat use by adult and young‐of‐year snail darters (Percina tanasi) in two rivers. Ecology of Freshwater Fish 2010: 19: 609–617. © Published 2010. This article is a US Government work and is in the public domain in the USA. Abstract – We characterised microhabitat availability and use by adult and young‐of‐year (YOY) snail darters (Percina tanasi Etnier 1976 ) while snorkelling in the French Broad and Hiwassee rivers, TN, USA. Both age groups of snail darters disproportionately used most microhabitat variables compared to their availability. Snail darters primarily occupied moderately deep, swift water over gravel substrates with little macrophyte coverage and no silt. Univariate comparisons indicated that adult and YOY darters occupied different habitat, but there was no marked differences between principal components analysis plots of multivariate microhabitat use within a river. Although the availability of microhabitat variables differed between the French Broad and Hiwassee rivers, univariate means and multivariate plots illustrated that the habitats used were generally similar by age groups of snail darters between rivers. Because our observations of habitat availability and use were constrained to low flow periods and depths <1 m, the transferability of our results to higher flow periods may be limited. However, the similarity in habitat use between rivers suggests that our results can be applied to low‐normal flow conditions in other streams.     

Histological alterations in gills of shrimp Litopenaeus vannamei in low‐salinity waters under different stocking densities: Potential relationship with nitrogen compounds

Two experimental modules with different stocking densities (M1 = 70 and M2 = 120 shrimp /m²) were examined weekly over a culture cycle in tanks with low‐salinity water (1.9 g/L) and zero water exchange. Results showed survival rates of 87.7 and 11.9% in M1 and M2, respectively. Water temperature, pH, dissolved oxygen, electrical conductivity and chlorophyll a were not significantly (p > .05) different between modules. In contrast, the concentrations of nitrogen compounds were significantly (p < .05) different between modules, except nitrite‐N (M2 were 2.31 ± 1.38 mg/L N‐TAN, 0.18 ± 0.49 mg/L N‐NO₂^? and 6.83 ± 6.52 mg/L N‐NO₃^?; in M1: 0.97 ± 0.73 mg/L N‐TAN, 0.05 ± 0.21 mg/L N‐NO₂^? and 0.63 ± 0.70 mg/L N‐NO₃^?). When waters of both modules reached higher levels of ammonia and nitrite, histological alterations were observed in gills. The histological alterations index (HAI) was higher in M2 (5‐112) than in M1 (2‐22).     

Effects of light spectrum and intensity on growth,survival and physiology of leech (Whitmania pigra) larvae under the rearing conditions

Used as a traditional Chinese medicine, the high mortality rate and slow growth of Whitmania pigra larvae are the most serious bottlenecks for the scale development of artificial breeding. Firstly, five light colour treatments (white, blue, green, red and yellow) were tested to determine effects of light spectrum on the growth of larval W. pigra at the same intensity of 70.00 μmol m^?2 s^?1. The experiment lasted for 45 days. Under our experimental conditions, the weight gain (WG) and the specific growth rate (SGR) under blue light condition were significantly higher compared with the other treatments (P ≤ 0.05). It is reasonable to conclude that blue light can promote the leech growth. In addition, reared at five blue light intensity treatments (20.00 ± 3.84, 40.78 ± 4.18, 53.67 ± 5.98, 70.00 ± 7.26 and 87.33 ± 5.77 μmol m^?2 s^?1), the WG and SGR increased with increasing intensity. Meanwhile, they were significantly higher in the 70.00 and 87.33 μmol m^?2 s^?1 treatments (P ≤ 0.05). In the higher intensity light treatments, the digestive enzymes were higher and antioxidant enzymes were lower. These results suggest that the optimal light spectrum for the culture of W. pigra during the early life stage was blue and the optimal light intensity was higher light intensity (70.00–87.33 μmol m^?2 s^?1).     

Spatial scale effects on habitat associations of the Ashy Darter,Etheostoma cinereum,an imperiled fish in the southeast United States

Abstract – The ashy darter, Etheostoma cinereum, is an imperiled fish within the Cumberland and Tennessee drainages of the southeast United States. An understanding of habitat associations and the relationship of habitat use across multiple spatial scales are critical elements in its conservation. Our objectives were to quantify habitat associations at the stream reach and microhabitat scales for adult and juvenile darters, and to understand the linkage between the two scales based on gradients of habitat use. We focused our efforts within the Rockcastle River, Kentucky (Cumberland River drainage), because the watershed was known to contain a relatively large ashy darter population. Three hundred twenty‐two individuals were collected from 21 reaches. The species was restricted to the mainstem of the river and the lower reaches of the larger tributaries. The distribution and abundance of adult and juvenile darters differed significantly at each spatial scale, and both groups demonstrated non‐random use of the available habitat. Gradients of stream size and substrate size were identified as important factors. A threshold of environmental quality was determined based on the habitat use patterns among the two scales. Habitat use between the two scales was independent within the threshold, indicating that the specific quality of the microhabitats did not necessarily matter within a stream reach. However, beyond the threshold, a decrease of at least 48% in adult and juvenile darter abundance was seen, indicating that a sufficient network of suitable microhabitats is needed to support a good population of darters within a stream reach.     

Evaluation of selected metal nanoparticles on hatching and survival of larvae and fry of Indian major carp,rohu (Labeo rohita)

Different laboratory synthesized metal nanoparticles viz. Copper oxide (CuO), Zinc oxide (ZnO) and silver doped titanium dioxide (Ag‐TiO₂) were studied for their effect on hatching and survival of larvae and fry of Indian major carp, rohu, Labeo rohita both in direct application in tank water & coated onto tanks. Among these nanoparticles, CuO and ZnO nanoparticles exhibited highest percentage of hatching in both direct addition (78.0 ± 3.1% and 78.05 ± 4.2%, respectively) and coating onto tanks (58.6 ± 2.1% and 61.2 ± 2.7%, respectively) at 1 mg mL^?1 while least percentage of hatching was recorded in Ag‐TiO₂ nanoparticles irrespective of its concentration & mode of supplementation. Highest survival of L. rohita fry (50.13 ± 2.2%) was observed after 15 days post hatching in CuO coated tanks followed by ZnO coated tanks (38.6 ± 2.8%) while least was recorded in Ag‐TiO₂ coated tanks (22.53 ± 3.0%). However in control tanks coated with Poly‐Urethane base with hardener and uncoated control tanks, the survival was 42.4 ± 1.2% and 41.36 ± 1.8% respectively. Further, significantly lower microbial load of water was recorded in CuO nanoparticles coated tanks (1.5 × 10¹⁰ CFU L^?1) as compared to uncoated control tanks (1.1 × 10¹⁶ CFU L^?1) without affecting water quality parameters. On the other hand, in Ag‐TiO₂ coated tanks, significantly lower microbial load (1.0 × 10⁶ CFU L^?1) as compared to uncoated control tanks at 15 days post hatching was recorded. However, Ag‐TiO₂ was toxic to L. rohita larvae & fry both in direct application and coating onto tanks. Considering the beneficial effects of CuO nanoparticle application, it has the scope of being used in a more eco‐friendly way in hatchery operations.     

Constructed wetlands for treatment of harvest effluents from grow‐out ponds of the Amazon river prawn

Effluent discharges from aquaculture can reduce water quality in receiving water bodies and that strategies or practices to reduce this are necessary. One possibility is to reduce, or eliminate, water renewal in grow‐out ponds. In this study, we eliminated water renewal in grow‐out ponds associated with the culture of 40 individuals m^?2 of Amazon river prawn (Macrobrachium amazonicum). At the end of the culture period it was, however, necessary to drain the pond to harvest the prawns. An experiment was performed in triplicate, in which the water supply characteristics and harvest water characteristics of ponds were evaluated. To reduce these concentrations of total N and P, an aquatic macrophyte (Eichhornia crassipes, water hyacinth) treatment system (CWs) was adopted. The water characteristics in the CWs were evaluated after 1, 3, 7, 14 and 21 days. The water supply of ponds presented the average concentrations of 0.67 ± 0.32 mg L^?1 and 17.4 ± 14.7 μg L^?1 of total‐N and total‐P respectively. The harvest effluent of ponds had elevated concentrations of different forms of nitrogen (4.44 mg L^?1 of total‐N) and phosphorous (100.9 μg L^?1 of total‐P). After 1 day of the experiment we found the following reductions in key nutrients in treatment system containing E. crassipes: 90%, 78% and 45% reductions in the concentrations of particulate matter, orthophosphates and nitrates respectively. We noted that after 3 days the nitrates had been reduced by 53%. We concluded that 3 days of this treatment was sufficient for the removal of the additional nutrients that had accumulated in the Amazon river prawn ponds.     

Growth differences of Japanese eels Anguilla japonica between fresh and brackish water habitats in relation to annual food consumption in the Kojima Bay‐Asahi River system,Japan

To learn about the relationships between feeding and growth of temperate eels in freshwater and brackish water habitats, we analysed 533 yellow‐phase Japanese eels Anguilla japonica collected in both types of habitats in southeastern Japan. Because male eels were very rare in each habitat (FW, N = 1; BW, N = 20), characteristics of female eels were compared between the different habitats. Annual food consumption was evaluated with the consideration of instantaneous food consumption and annual activity period. Stomach fullness index (stomach content weight/body weight) was used as an indicator of instantaneous food consumption. The ratios of number of months with eel catch to those when eel sampling was conducted were used as an indicator of activity period. Female yellow eels tended to be older and slower growing in fresh water (N = 78; age, mean ± SD = 7.9 ± 2.4 years; growth rate, 59.8 ± 14.0 mm year^?1) than in brackish water (N = 229; age, 5.5 ± 1.8 years; growth rate, 90.1 ± 24.4 mm year^?1). Irrespective of sex, yellow eels in brackish water had a higher stomach fullness index and a greater ratio of months with eel catches, indicating greater annual food consumption by brackish water eels. These results indicate that greater annual food consumption contributes to the greater growth rates of Japanese eels in brackish water habitats.     

Dietary tryptophan requirement of fingerling Catla catla (Hamilton) based on growth,protein gain,RNA/DNA ratio,haematological parameters and carcass composition

A 12‐week feeding trial was conducted in eighteen 70 L indoor polyvinyl circular troughs provided with a water flow‐through system (1–1.5 L min^?1) at 28 ± 1 °C to evaluate the dietary tryptophan requirement of fingerling Catla catla (3.45 ± 0.24 cm; 0.60 ± 0.13 g). Six casein‐gelatin‐based amino acid test diets (330 g kg^?1 crude protein; 13.6 kJ g^?1 digestible energy) containing graded levels of L‐tryptophan (1.0, 1.4, 1.9, 2.3, 2.8, 3.4 g kg^?1 dry diet) were fed to triplicate groups of fish near to satiation at 08:00, 12:30 and 17:30 h. Absolute weight gain, feed conversion ratio, protein gain, RNA/DNA ratio, hepatosomatic index, viscerosomatic index, condition factor and haematological indices improved with the increasing levels of tryptophan from 1.0 to 2.3 g kg^?1 of dry diet. Significantly higher carcass protein was obtained at 2.3 g tryptophan per kilogram of the dry diet. Exponential analysis of absolute weight gain, feed conversion ratio, protein gain and RNA/DNA ratio against dietary tryptophan levels at 95% maximum and minimum responses displayed the tryptophan requirement at 2.5, 2.3, 2.5 and 2.1 g kg^?1 dry diet, respectively. Inclusion of dietary tryptophan in the range of 2.1–2.5 g kg^?1 dry diet, equivalent to 6.4–7.6 g kg^?1 dietary protein, is recommended in formulating tryptophan‐balanced feed for the culture of this fish species.     

Effect of shading colours on growth and pigment content of Gracilaria fisheri (Xia & Abbott) Abbott,Zhang & Xia (Gracilariales,Rhodophyta)

Sporeling and tissue propagation of agarophytic seaweed, Gracilaria fisheri, aimed to investigate the optimal shading colour for the preservation. This study was conducted under different shading colours indoor and outdoor experiments. The indoor experiment: tissues and sporelings of the seaweed were cultured in plastic chambers under fluorescent lights and were wrapped with white, green, blue and red colour PVC sheets of light intensity of 20 ± 1 μmol m^?2 s^?1. The outdoor tissues were cultured in the plastic tanks under different shadings of Saran sheets: white, green, blue and black covering the hoop‐houses with light intensity of 110 ± 10 μmol m^?2 s^?1. The results showed that different shading colours strongly influenced growth of G. fisheri sporelings and tissues but little effect on pigmentation. After 40 days, the highest growth rates of G. fisheri tissues and sporelings were found under red light with 1.44 and 1.89% day^?1 respectively. There was no significant difference (P > 0.05) on pigment content of tissues indoor, whereas it was found that chlorophyll concentration of the sporelings under green light with 416.8 μg g^?1 fresh weight was significantly higher (P < 0.05) than those in other treatments. After 8‐week culture, outdoor tissues showed the highest growth rate with 1.71% day^?1 in the green hoop‐house. The study has found that G. fisheri cultivation was less influenced by epiphytes in the back hoop‐house with 15%. This study showed the feasibility of successful cultivation of G. fisheri sporelings and tissues.     

Use of marine by‐product meals in diets for juvenile longfin yellowtail Seriola rivoliana

A 60‐day feeding trial to determine the nutritional value of marine by‐product meals in diets for longfin yellowtail Seriola rivoliana juveniles (48.1 ± 0.6 g initial weight) was conducted. Five diets were evaluated: a reference diet (RD; 500 g kg^?1 CP, 130 g kg^?1 L), containing 500 g kg^?1 of fish meal (FM); three experimental diets with 125 g kg^?1 of shrimp head (SM), Catarina scallop viscera (CM) or Pen shell viscera (PM) meals; and one diet (SCP) containing 125 g kg^?1 of each of the experimental meals, to partially replace FM. Survival was not significantly affected by any treatment. Individual weight gain per day was high for the PM (5.3 ± 0.51 g d^?1) and SM (4.7 ± 0.32 g d^?1) diets, being significantly higher than the RD (3.5 ± 0.23 g d^?1) and the other treatments (<1.2 g d^?1). Feed intake was high in PM and SM diets, and very low in SCP and CM diets. Biochemical and haematological parameters were similar among treatments RD, PM and SM, while fish fed CM and SCP exhibited lower levels of total protein, cholesterol, haematocrit and haemoglobin. The results indicate that SM or PM can be used to partially replace FM in diets for yellowtail juveniles.     

The effect of flow on the competition between the alien racer goby and native European bullhead

The racer goby is an invasive Ponto‐Caspian fish spreading throughout Europe. They threaten a native species of similar biology, the European bullhead, by displacing them from shelters. These shelters are necessary for reproduction as well as for protection against predators and hydrodynamic forces. However, abiotic conditions may strongly modify the outcome of an interspecific competition in the wild. Nevertheless, little is known of the effect of flow velocity on the competition between these rheophilic species, although this factor is crucial for their distribution in the field. We video‐recorded fish behaviour for 2 h in single‐species and mixed‐species pairs in the presence of single shelters at three flow velocities: 0, 10 (a velocity preferred by the racer goby) and 30 cm·s^?1 (a velocity greater than preferred by the racer goby) to determine whether the invader can deprive the native species of its shelter. At the flow of 0 and 10 cm·s^?1, the racer goby exhibited aggressive behaviour towards bullhead, and this restricted the time spent by the bullhead in the shelter. Moreover, although the flow of 30 cm·s^?1 inhibited racer goby aggression, the time spent by the bullhead in the shelter in interspecific competition was still reduced when compared to intraspecific controls. Our results suggest that under natural conditions, the racer goby displace bullheads from their shelters even at flow velocities greater than optimal for the racer goby.     

High feeding and growth rates in common octopus (Octopus vulgaris) fed formulated feeds with an improved amino acid profile and mixture of binders

Four semi‐moist formulated feeds were supplied to Octopus vulgaris subadults (664 ± 70 g; 18.4 ± 0.7°C) in two different experiments. In the experiment #1, two diets were prepared with a new mixture of binders (gelatine 150 g kg^?1, starch 100 g kg^?1 and gum 50 g kg^?1). The GEL15‐Squid and GEL15‐Hake feeds included 100 g kg^?1 freeze‐dried squid (Todarodes sagittatus) or hake (Merluccius sp.) respectively. Both feeds showed low water disintegration rates at 24 h (13.6–15.0% dry weight). The specific feeding rate was higher in animals fed GEL15‐Hake (2.7%BW day^?1), but the growth and feed efficiency were significantly better in animals fed GEL15‐Squid (1.4%BW day^?1 and 61.2% respectively; P < 0.05). The proximate composition of the digestive gland, carcass and whole animals was similar. In the experiment #2, the GEL15‐Squid amino acid profile was improved by replacing 50 g kg^?1 gelatine by 50 g kg^?1 freeze‐dried squid (GEL10‐Squid) or freeze‐dried fish (GEL10‐Fish). These feeds showed higher water disintegration rates (31.7–36.3% dry weight). The feeding rates (2.2–2.3%BW day^?1), growth (1.5%BW day^?1) and feed efficiency were similar for both diets. Total lipids were higher in the digestive gland and whole animals fed GEL10‐Fish diet (P < 0.05). Future effort could be directed towards alternative binders that allow improve amino acid balance with a minimum gelatine content or even supplementation trials including essential amino acids.     

Investigation of tetracycline and degradation products in Euphrates river receiving outflows of trout farms

In this study, tetracycline (TC), epitetracycline (ETC), 4‐epianhydrotetracycline (EATC) and anhydrotetracycline (ATC) concentrations were determined in the surface waters carrying outflows of trout farms. The samples were taken from downstream of Keban Dam and upstream of Karakaya Dam Lake, which are located in the Euphrates and Tigris River Basin. The occurrence of TC and degradation products (DPs) was proved in the sampling points which take the outflows of the trout farms. Tetracycline and DPs were under the detection limits in sampling points where the trout farms do not exist. The highest TC concentration was detected as 50.0 ± 2.5 μg L^?1 (1st week), whereas the lowest TC concentration was 8.2 ± 0.41 μg L^?1 (7th week). The highest ETC concentration was 88.1 ± 4.4 μg L^?1 (3rd week)and the lowest ETC concentration was 9.4 ± 0.4 μg L^?1 (3rd week). The highest and lowest EATC concentrations were detected as 35.8 ± 1.8 μg L^?1 (2nd week) and 8.2 ± 0.4 μg L^?1 (2nd week) respectively. The highest ATC concentration was 28.3 ± 1.4 μg L^?1 (3rd week), whereas the lowest was 6.54 ± 0.34 μg L^?1 (7th week). Tetracycline and DP concentrations detected in surface waters followed the following order: ETC>TC>EATC>ATC.