Response of downstream migrating adult European eels (Anguilla anguilla) to bar racks under experimental conditions

Russon IJ, Kemp PS, Calles O. Response of downstream migrating adult European eels (Anguilla anguilla) to bar racks under experimental conditions.
Ecology of Freshwater Fish 2010: 19: 197–205. © 2010 John Wiley & Sons A/S Abstract – The behavioural response of downstream migrating nonsalmonid fish to hydraulic conditions associated with river infrastructure is poorly understood. The response of downstream migrating adult European eels (Anguilla anguilla) to bar racks (12 mm bar spacing) angled on the vertical and horizontal planes under different flow regimes and during periods of darkness was assessed. Eels predominantly moved along the channel floor and wall, tending to follow routes where turbulence intensity was high. Time taken to approach the racks was greater than expected if fish had moved passively with the flow. Eels did not exhibit clear avoidance behaviour prior to encountering the racks, instead marked changes in behaviour occurred only after physical contact was made with the structure. No impingement or passage through the racks occurred, and passes per approach were high (98.3%), when vertical racks were angled 15°, 30° or 45° relative to the flow. Impingement and passage through the racks only occurred when horizontally inclined racks were placed perpendicular to the flow. The time eels were impinged on the racks was negatively related to discharge when angled at 30° relative to the channel floor, and positively related when upright. Frequency of impingement was higher under low discharge (132.9 ± 16.6 l·s^?1). Impinged eels escaped from racks at approach velocities of 0.90 ± 0.05 m·s^?1. Passage through the upright rack was common under high discharge (278.9 ± 36.2 l·s^?1). The information presented will improve current fish passage criteria for European eels that are required to develop more effective fish passage facilities.     

Development of a feeding strategy for silver perch, Bidyanus bidyanus (Mitchell), based on restricted rations

To develop a feeding strategy for the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell), a series of eight experiments was done in 1 m³ cages in an aerated, earthen pond to determine the effects of feeding rate (% body weight) and feeding frequency (no. of feeds day^?1) on the growth and feed conversion ratio (FCR) of fingerlings and larger fish under ambient water temperatures over the range 13.8–30.6°C. Fish were fed extruded pellets of a silver perch diet containing 34% digestible protein and 14 MJ kg^?1 digestible energy. Commercial silver perch farmers were consulted about feeding practices for large fish (>500 g) and at water temperatures below 12°C, and winter feeding practices for other warmwater species were used to complete the strategy. In the feeding experiments, growth and FCR increased with increasing feeding rates to a level above which only FCR increased. Optimal feeding rates and frequencies were those which resulted in maximal growth, while minimizing effort (feeding frequency) and FCR. The highest feeding frequency required for maximal growth, including that of small fingerlings was twice (2 ×) daily, and the optimal feeding rates varied with water temperature and size of fish. The optimal daily regimes were: small fingerlings (initial mean weight, 2.0 g) 7.5% 2 × at a mean temperature of 23.3°C; fingerlings (14.9–27.7 g) 7.5% 2 × at 27.1°C, 5.0% 2 × at 23.7°C and 2.0% 1 × at 16.8°C; and large silver perch (162.5–510.6 g) 0.5% 1 × daily or 1.0% on alternate days at 15.6°C, 1.0% 1 × at 17.3°C, 3.0% 2 × at 24.1°C and 2.0% 2 × at 27.9°C. It is suggested that regimes of 0.5% 1 × daily for fingerlings (<50 g) and 0.5% 1 × on alternate days for larger fish are used at temperatures of 9–12°C, and 0.5% 3 days week^?1 and 0.5% 1 day week^?1 for fingerlings and larger fish, respectively, at 6–9°C. Feed inputs should not exceed 150 kg ha^?1 day^?1 in ponds less than 0.3 ha and 100 kg ha^?1 day^?1 in larger ponds. Our research has established a feeding strategy for silver perch based on restricted rations.     

Effect of fish size and temperature on the utilization of different protein sources in two catfish species

Two sets of feeding trial were conducted to determine the effect of size and temperature on the utilization of different protein sources in two catfish species. In both the experiments, the fish were fed to apparent satiation daily at 08.00 and 18.00 hours, and faecal matter collected through slow siphoning. The first experiment was designed to study the effect of fish size on apparent digestibility coefficients for plant and animal proteins in the African catfish, Clarias gariepinus (Burchell, 1822). Three size classes (105–109 g; 780–830 g; 1250– 1300 g) of fish were stocked in triplicate sets of 600‐L plastic pools fitted with a flow‐through system (2 L min^?1). Within each size class, the apparent digestibility coefficient (ADC) for protein varied significantly with the source and quality of protein used. Soybean meal and fishmeal protein were utilized with greater efficiency, whereas rice bran protein was least digestible. An increase in ADC protein was apparent with increase in fish size for high protein sources such as soybean meal, full‐fat soybean, laboratory‐prepared fishmeal, steam‐cooked brown fishmeal and dried fish. ADC protein for other ingredients decreased with increase in size. In the second experiment, the influence of varying temperature on ADC for protein was determined in the catfish, Heteropneustes fossilis (Bloch) (6–8 g). Triplicate groups of 25 fish were kept at three different ambient temperatures (18, 28 and 38 °C), in 70‐L polyvinyl indoor flow‐through (1–1.5 L min^?1) circular tanks (water volume = 55 L). The trend in utilization of protein from different sources remained similar at the three temperatures. For each ingredient, digestibility values obtained at 18 °C were significantly lower than those obtained at 28 °C and 38 °C. Optimal protein utilization in H. fossilis was measured at 28 °C.     

Food consumption and digestive enzyme activity of Clarias batrachus exposed to various temperatures

The effect of temperature on the food consumption rate and the digestive enzyme activities of Clarias batrachus (80.60 ± 5.34 g) were evaluated. Fish were exposed to six different temperatures of 10, 15, 20, 25, 30 and 35 °C following an acclimation temperature of 25 °C. The rate of temperature change was 2 °C day^?1. Highest food consumption was recorded at 25 °C. It gradually reduced with decreasing water temperature. Food consumption rate was significantly (P < 0.05) lower at 10 °C compared with other treatments. Hence, 46.67, 8.20–23.58 and 1.02–6.15% reduced food consumptions were recorded in groups exposed at 10, 15 and 20 °C temperatures, respectively, compared with the 25 °C. The consumption rate was not affected in fish exposed at 30 and 35 °C. Total protease, trypsin and chymotrypsin activities were significantly (P < 0.05) higher in fish exposed at 25 °C compared with others. Lipase activity was significantly (P < 0.05) higher in fish exposed at 30 °C compared with others. Lowest enzyme activities were recorded at 10 °C. Water temperature below 25 °C affected the food consumption and digestive enzyme activities in fish that served as indicators of stress in fish.     

Adapting bioenergetic factorial modelling to understand the implications of heat stress on barramundi (Lates calcarifer) growth,feed utilisation and optimal protein and energy requirements – potential strategies for dealing with climate change?

The implications of temperature on bioenergetics for barramundi (Lates calcarifer) were defined in an improved factorial model that encompassed revised parameters accounting for effects over the temperature range of 16–39 °C and size range of 10–3000 g. A revised growth function describing weight gain by barramundi as a function of fish weight and temperature was derived from farm and laboratory data and included a term for a shift in optimal temperature with fish size: Gain (g fish^?1 day^?1) = (K + xT + yT ² + zT³) * (weight)^ax+b. Maintenance energy and protein demand functions were also derived on a similar form, and all three functions combined to form the basis of a factorial model for energy and protein demand. Using this model, optimal iterative feed specifications were defined for a range of fish sizes at temperatures of 25, 30 and 35 °C. A feed demand model was also developed based on the demand for digestible energy (DE) at each of these temperatures. The model shows that at high temperatures (35 °C), there is an increase in digestible protein (DP) to DE demand, and that with increasing size, there is a decrease in the DP to DE demand.     

Pattern of feed intake in four species of fish under commercial farming conditions: implications for feeding management

Meal duration and feed ingestion rate were measured in sea cage-reared Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, yellowtail Seriola quinqueradiata and red sea bream Pagrus major fed dry extruded feed in discrete meals. At the population level, satiation times in yellowtail, salmon and trout were typically about 15–25 min, but time to satiation was longer (60–90 min) in red sea bream. In all species, feed ingestion rate declined progressively during the course of the meal as the fish became satiated. Initial feed ingestion rates in salmon were ≈ 0.3–0.5 kg feed tonne fish^–1 min^–1 and in trout 0.5–0.9 kg feed tonne fish^–1 min^–1, although the capacity to deliver feed may have restricted ingestion. Water temperature had little effect on ingestion rates, possibly because the number of meals per day (1–3) was varied with water temperature, and this may have standardized hunger level at the start of meals. Yellowtail ingested feed at ≈ 3.5 kg feed tonne fish^–1 min^–1 at water temperatures of 18 °C and 28 °C, whereas red sea bream ingested feed at initial rates of 0.6 and 1.4 kg feed tonne fish^–1 min^–1at 26.5 °C and 18 °C respectively. The findings are discussed in relation to feeding strategies to minimize interfish competition for feed and to improve the ability of fish farmers to detect the point at which fish are satiated.     

Ammonia nitrogen excretion in Mandarin Fish (Siniperca chuatsi) and Grass Carp (Ctenopharyngodon idellus) fed practical diets: the effects of water temperature

To understand the actual production of fish culture about the utilization of dietary protein and excreta impact on the environment between mandarin fish (Siniperca chuatsi) and grass carp (Ctenopharyngodon idellus), the study to investigate the effect of temperatures (19 ± 0.5°C, 24 ± 0.5°C and 29 ± 0.5°C) on ammonia‐N excretion in mandarin fish and grass carp under fed and fasted states was conducted. These two species were fed a practical diet containing 325.2 g kg^?1 crude protein at 3% body weight per day. The ammonia‐N excretion rate was significantly increased when temperature increased from 19 to 29°C, and a linear relationship between ammonia‐N excretion rate and temperature. The maximum ammonia‐N excretion levels of mandarin fish and grass carp were observed at 4–8 h and 2–4 h after feeding, respectively, and the minimum values for both species were observed at 24 h after feeding. Under the feeding condition, mandarin fish had a lower ammonia‐N excretion level compared to grass carp at 24°C and 29°C. The average amount of ammonia‐N excreted by mandarin fish at 24 h is significantly higher than grass carp under fasting conditions, except 19 ± 0.5°C. These results indicated that mandarin fish might make better use of protein at higher temperature than grass carp when fed practical diets in commercial production. These results of this study suggested that mandarin fish had a lower ammonia‐N excretion level compared with grass carp, making a less contribution to environmental loading in an intensive fish culture.     

Threshold values of river discharge and temperature for anglers' catch of Atlantic salmon,Salmo salar L.

Abstract The catch by anglers of adult Atlantic salmon, Salmo salar L., was studied over a 5-year period in the River Gaula, Norway. Atlantic salmon were caught over a wide range (23–570 m³ s^?1) of the observed extent of river discharge (13–950 m³ s^?1) and throughout the range of temperature (4–23 °C), but both factors strongly affected catch rate. Significant correlations between the number of Atlantic salmon caught daily, and water temperature (r = 0.33) and river discharge (r = ?0.42) were found in 1987 and 1989, respectively. The highest daily catch occurred between 50 and 150 m³ s^?1, and at temperatures between 13 and 16 °C. Threshold values for water discharge and temperature were found to exist at 250 m³ s^?1 and 8 °C, with the highest catches below and above these values, respectively.     

Lower lethal temperature of the endangered Rio Grande silvery minnow and its implications for propagation and reintroduction

The lower lethal temperature of the endangered Rio Grande silvery minnow, Hybognathus amarus, was estimated from survival rates of fish overwintered in above-ground tanks. Temperature went to 0.0°C both winters. In 2012–2013, survival of Age class 0 fish was 79.87%, and in 2013–2014, survival of Age class 1 fish was 97.1%, suggesting that if Rio Grande silvery minnow is subjected to seasonal temperature changes, lower lethal temperature is ≤0.0°C. Results show that heating hatchery water in the winter is unnecessary. Additionally, current management guidelines that preclude reintroduction of the species into river sections where winter temperatures are ≤1°C must be reevaluated.