Ontogeny of critical and prolonged swimming performance for the larvae of six Australian freshwater fish species

Critical (<30 min) and prolonged (>60 min) swimming speeds in laboratory chambers were determined for larvae of six species of Australian freshwater fishes: trout cod Maccullochella macquariensis, Murray cod Maccullochella peelii, golden perch Macquaria ambigua, silver perch Bidyanus bidyanus, carp gudgeon Hypseleotris spp. and Murray River rainbowfish Melanotaenia fluviatilis. Developmental stage (preflexion, flexion, postflexion and metalarva) better explained swimming ability than did length, size or age (days after hatch). Critical speed increased with larval development, and metalarvae were the fastest swimmers for all species. Maccullochella macquariensis larvae had the highest critical [maximum absolute 46·4 cm s^?1 and 44·6 relative body lengths (L_B) s^?1] and prolonged (maximum 15·4 cm s^?1, 15·6 L_B s^?1) swimming speeds and B. bidyanus larvae the lowest critical (minimum 0·1 cm s^?1, 0·3 L_B s^?1) and prolonged swimming speeds (minimum 1·1 cm s^?1, 1·0 L_B s^?1). Prolonged swimming trials determined that the larvae of some species could not swim for 60 min at any speed, whereas the larvae of the best swimming species, M. macquariensis, could swim for 60 min at 44% of the critical speed. The swimming performance of species with precocial life‐history strategies, with well‐developed larvae at hatch, was comparatively better and potentially had greater ability to influence their dispersal by actively swimming than species with altricial life‐history strategies, with poorly developed larvae at hatch.     

Schwimmverhalten und Schwimmgeschwindigkeit bei den Larven des HeringsClupea harengus

The present study is based on two year experiments; it analyses swimming behaviour and swimming speed at different developmental stages of the herring. Yolk sac larvae tend to sink rather rapidly during resting phases. At the end of the yolk sac stage the sinking rate is at its minimum; it increases again with increasing larva size. During the phase of yolk sac resorption, vertical movements become gradually transformed into horizontal ones. Generally, three types of swimming can be distinguished: (1) “Abrupt swimming” consisting of very short periods of fast swimming; normally each dart is connected with a change in swimming direction. (2) “Normal swimming” characterized by steady movements for several seconds; it results in a winding path. (3) “Slow meandering” representing search swimming, a slowly winding locomotion with a large amplitude of each winding but with very little net progression of the larva. Swimming speed varies considerably in all size groups. The 8 to 11 mm (total length) larvae reach a mean swimming velocity (undulation) of 1.0 to 1.2 cm per second. Swimming speed, measured as the straight line distance between start and end points of a single swimming phase, attains mean values of 7 to 8 mm/sec in 8 to 11 mm larvae, 10 to 11 mm/sec in 11 to 15 mm larvae, 21 to 25 mm/sec in 19 to 24 mm larvae, and 40 to 50 mm/sec in 32 to 40 mm larvae. Swimming activity changes during larval development and seems to be influenced by food supply. The total distance travelled in 5 minutes by the head of a yolk sac larva is 1 to 3 m. About 8 days after hatching, sinking rate is low and “search swimming” (slow meandering movements) prevails. The path covered by the head within 5 minutes is 0.8 to 1.5 m.     

Effect of water velocity and temperature on energy use,behaviour and mortality of pallid sturgeon Scaphirhynchus albus larvae

Natural reproduction of pallid sturgeon Scaphirhynchus albus has been limited for decades and a recruitment bottleneck is hypothesized to occur during the larval stage of development. In this study, we evaluated the effects of water velocity and temperature on the swimming activity, energy use, settling behaviour and mortality of endogenously feeding larvae. The swimming activity of drifting sturgeon larvae (i.e., fish exhibiting negative rheotaxis) increased at low water velocity. In subsequent experiments, we observed greater energy depletion and resultant mortality of larvae in no-flow environments (0 cm s⁻¹) compared to tanks with water velocity ranging from 3.5 to 8.3 cm s⁻¹. The growth rate of drifting larvae was positively related to water temperature (18.7–23.3°C), but reduced growth rate at low water temperature (18.7°C) resulted in protracted development that extended average drift duration by ~4 days compared to larvae reared at 23.3°C. This study provides evidence that cooler summer water temperatures, characteristic of present-day conditions in the upper Missouri River, can reduce larval development and extend both the drift duration and distance requirements of S. albus. Moreover, if dispersed into low velocity environments, such as in reservoir headwaters, larvae may experience increased mortality owing to a mismatch between early life stage drift requirements and habitat conditions in the river. Manipulation of water releases to increase seasonal water temperature below dams may aid survival of S. albus larvae by shortening the time and distance spent drifting.     

茉莉酸甲酯诱导邻近番茄植株抗斜纹夜蛾的浓度和距离效应

茉莉酸甲酯(Methyl jasmonate, MeJA)与植物间的防御通讯密切相关,其挥发性强,可以在空气中传播而诱导邻近植物产生防御反应,为探明MeJA诱导邻近植株抗虫性的浓度和距离效应,本研究在大棚(长4 m×宽1 m×高1 m)进口处喷以不同浓度MeJA,检测离气味源60 cm、120 cm、180 cm、240 cm和300 cm远的番茄植株叶片多酚氧化酶(Polyphenol oxidase, PPO),过氧化物酶(Peroxidase, POD)和脂氧合酶(Lipoxygenase, LOX)的活性以及斜纹夜蛾幼虫取食不同处理番茄植株叶片后的体重增长率,研究结果表明1 mmol/L和10 mmol/L MeJA挥发物可以显著诱导增强邻近番茄植株叶片PPO,POD和LOX酶的活性,以离10 mmol/L MeJA气味源60 cm处植株叶片的酶活性最高,并随着距离的增加而呈降低的趋势;取食60 cm和300 cm对照组植株叶片的斜纹夜蛾幼虫其体重增长率没有显著差异,然而1 mmol/L和10 mmol/L MeJA处理下,取食300 cm处植株叶片的斜纹夜蛾幼虫其体重增长率显...     

Respiratory metabolism of the soft tick,Ornithodoros turicata (Dugès)

The rate of oxygen consumption was investigated in fed larval, nymphal and adult Ornithodoros turicata ticks and in starved nymphal and adult ticks. Oxygen consumption rate of fed adult ticks increased with increasing temperature. The metabolic rate of adult ticks was affected by starvation whereby starved adult ticks showed a significantly lower oxygen consumption than their fed counterparts. The oxygen consumption rate of fed female ticks was significantly higher than that of fed males but, there was no significant difference between the oxygen consumption rates of starved female versus starved male ticks. Oxygen consumption of fed larvae was significantly greater than those of fed first through third instar nymphs. Fed and starved nymphal ticks as well as fed adult ticks ventilated continuously. In contrast, starved adults ventilated discontinuously. The ability to reduce metabolic rate, plus the capability to ventilate discontinuously allow O. turicata adults to cope with prolonged starvation.     

The effect of hunger on intraspecific interactions between first-instarSinea diadema (Hemiptera: Reduviidae)

Fed and unfed first instars of the spined assassin bugSinea diadema were paired to evaluate the effects of food deprivation on their behaviour during encounters. Fed nymphs encountering starved 5-day-old nymphs retreated from 69% of the encounters after contacting the starved nymph. In contrast, starved nymphs initiated grappling during 30% of the encounters with fed nymphs and retreated significantly less often than the fed nymphs. When a single fed nymph was placed together with two unfed 3-day-old nymphs in a closed arena, the fed nymphs generally were not the first nymph cannibalized and were the final survivors in 67% of 24 replicates. These results are discussed in the context of the relative costs and benefits of escalating or retreating from encounters.     

寄主植物对松墨天牛幼虫体内酶系活性的影响

室内采用在马尾松、黑松、火炬松、湿地松和雪松皮下接入松墨天牛Monochamus alternatus Hope幼虫的方法,探明5种寄主植物对松墨天牛幼虫的存活、钻蛀取食及纤维素酶、酯酶、羧酸酯酶活性的影响。结果表明,5种寄主植物对松墨天牛幼虫存活和钻蛀取食有显著影响,接种于马尾松的天牛幼虫存活率100%;接种于雪松的松墨天牛幼虫存活率仅55.56%。松墨天牛取食不同寄主后,其体内纤维素酶、酯酶和羧酸酯酶活性存在显著差异。其中以取食火炬松的Cx酶活性最高,为(4.5754±0.1975)μmol·g-1(FW)·min-1,C1酶和β-l,4-葡萄糖苷酶活性以取食马尾松的松墨天牛幼虫消化道中最高,分别为(2.8199±0.0510)μmol·g-1(FW)·min-1与(3.0793±0.1733)μmol·g-1(FW)·min-1;而以取食黑松和马尾松的酯酶、羧酸酯酶活性最高,分别为1372.74mmoD/min·μg和744.82mmoD/min·μg。     

Evaluation of swimming performance for fish passage of longnose dace Rhinichthys cataractae using an experimental flume

The swimming performance of longnose dace Rhinichthys cataractae, the most widely distributed minnow (Cyprinidae) in North America, was assessed in relation to potential passage barriers. The study estimated passage success, maximum ascent distances and maximum sprint speed in an open‐channel flume over a range of water velocities and temperatures (10·7, 15·3 and 19·3° C). Rhinichthys cataractae had high passage success (95%) in a 9·2 m flume section at mean test velocities of 39 and 64 cm s^–1, but success rate dropped to 66% at 78 cm s^–1. Only 20% of fish were able to ascend a 2·7 m section with a mean velocity of 122 cm s^–1. Rhinichthys cataractae actively selected low‐velocity pathways located along the bottom and corners of the flume at all test velocities and adopted position‐holding behaviour at higher water velocities. Mean volitional sprint speed was 174 cm s^–1 when fish volitionally sprinted in areas of high water velocities. Swimming performance generally increased with water temperature and fish length. Based on these results, fishways with mean velocities <64 cm s^–1 should allow passage of most R. cataractae. Water velocities >100 cm s^–1 within structures should be limited to short distance (<1 m) and structures with velocities ≥158 cm s^–1 would probably represent movement barriers. Study results highlighted the advantages of evaluating a multitude of swimming performance metrics in an open‐channel flume, which can simulate the hydraulic features of fishways and allow for behavioural observations that can facilitate the design of effective passage structures.     

Critical swimming speeds of wild‐caught sand‐smelt Atherina presbyter larvae

Swimming abilities of wild‐caught sand‐smelt Atherina presbyter larvae were assessed as critical swimming speed (U_crit) throughout ontogeny. The mean U_crit increased with size, ranging from 3·6 to 18·7 cm s^?1, over the size range of 6·6–21·0 mm L_T. This indicates that at hatching A. presbyter larvae, far from being passive floaters, are already capable of active behaviours, which may influence their dispersal patterns.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Sugar feeding reduces short-term activity of a parasitoid wasp

Abstract.  Adding sugar to agricultural habitats is expected to enhance pest control by improving the longevity and physiological status of parasitoids. How a sugar diet and physiological parameters affect the host-foraging behaviour of Diadegma insulare , a parasitoid of diamondback moth larvae ( Plutella xylostella ), is investigated in the laboratory. Newly-emerged females are given water or sucrose-water ad libitum for 1 day, and then monitored for movement onto and away from a single cabbage leaf infested with 30 host larvae for 1 h. A significantly lower percentage of sucrose-fed females enter the host patch than those with access to only water (starved) females (60% vs. 91%). Of the females that enter the patch, fed wasps spend significantly less time in the patch than starved wasps (32.2 vs. 25.7 min) but feeding does not significantly affect oviposition rate. Fed and starved females sting six to seven larvae, and 19–29% of females superparasitize host larvae. Wasps with higher levels of fructose are less likely to enter the host patch than wasps with lower fructose levels. The lower proportion of fed wasps entering the patch may be due to a period of inactivity after sugar feeding.     

Negative Phototaxis in Blepharisma japonicum

The protozoan Blepharisma japonicum showed negative phototaxis caused by transient reversal of the direction of ciliary beat and changes of swimming velocity induced with varying intensities of light. The ciliary reversal occurred at 1–2 sec after a sudden increase in light intensity. When light intensity was decreased, no response was observed. Moreover, the ciliates swam fast in light areas but slowly in dark areas; the mean velocity of swimming was 80 μ m/sec at 5 × 10² lux but reached about 400 μMm/sec at 5 × 10³ lux. In addition, the cell body elongated in response to light application; the mean length of the body was 308 μm at 5 × 10² lux, which increased to 397 μ m at 10⁴ lux. Such body elongation seems to contribute to rapid swimming. Negative phototaxis may be an important behavior in B. japonicum because the organisms are killed by exposure to strong light.     

The effect of spine postures on the hydrodynamic drag in Epinephelus ongus larvae

Laboratory behavioural observation and computational fluid dynamics (CFD) analysis were conducted to examine whether the movement of the elongated dorsal and pelvic spines changed the hydrodynamic drag in white‐streaked grouper Epinephelus ongus larvae. The behavioural observation in the tank revealed that the larvae extended the dorsal and pelvic spines during passive transport and retracted during swimming; the angles of the dorsal and pelvic spines in relation to the anteroposterior axis were larger during the passive transport (mean ± s.d . = 28·84 ± 14·27 and 20·35 ± 15·05°) than those during the swimming (mean ± s.d . = 2·59 ± 5·55 and 0·32 ± 6·49°). The CFD analysis indicated that the relative hydrodynamic drag acting on the larvae was approximately 1·25 times higher when the spines were extended (passive transport) than when the spines were retracted (swimming), suggesting that the E. ongus larvae have an ability to adjust their hydrodynamic drag depending on the behavioural context.     

Differences in the energetic cost of swimming in turbulent flow between wild,farmed and domesticated juvenile Atlantic salmon Salmo salar

Domestication has been shown to have an effect on morphology and behaviour of Atlantic salmon (Salmo salar). We compared swimming costs of three groups of juvenile Atlantic salmon subject to different levels of domestication: (1) wild fish; (2) first generation farmed fish origination from wild genitors; and (2) seventh generation farmed fish originating from Norwegian aquaculture stocks. We assessed swimming costs under two types of turbulent flow (one mean flow velocity of 23 cm s^?1 and two standard deviations of flow velocity of 5 and 8 cm s^?1). Respirometry experiments were conducted with fish in a mass range of 5–15 g wet at a water temperature of 15° C. Our results confirm (1) that net swimming costs are affected by different levels of turbulence such that, for a given mean flow velocity, fish spent 1·5‐times more energy as turbulence increased, (2) that domesticated fish differed in their morphology (having deeper bodies and smaller fins) and in their net swimming costs (being up to 30·3% higher than for wild fish) and (3) that swimming cost models developed for farmed fish may be also be applied to wild fish in turbulent environments.     

EFFECT OF STARVATION ON LIPOPHORIN DENSITY IN FIFTH INSTAR LARVAL Manduca sexta

Lipophorin (Lp) is a major insect lipoprotein and is responsible for lipid transport between organs. In this study, the effect of starvation on Lp properties was analyzed in larval Manduca sexta during the fifth instar. Lp hemolymph concentrations in larvae at days 1 and 2 were around 2–3 mg/ml and at day 3 it increased to 8 mg/ml. When larvae were starved for 24 h, they did not grow, but their body mass and hemolymph volume did not decrease significantly. Differences in Lp densities were observed. In fed larvae, from days 1 to 4, two major Lp populations were found with densities of 1.124 ± 0.002 (high density Lp‐larval₁, HDLp‐L₁) and 1.141 ± 0.002 g/ml (HDLp‐L₂). When larvae were starved for 24 h, only one Lp population was present, with density 1.114 ± 0.001 g/ml (HDLp‐L_s). When larvae were abdominally ligated at day 1 or 2 of fifth instar, only HDLp‐L_s was found after 24 h, indicating that the formation of this HDLp population was not dependent on any factor released by head. On the other hand, larvae that were ligated at day 3 showed the same Lp populations as the fed ones. In 24‐h starved larvae, lipid load in Lp was higher as compared to the fed controls. In 24‐h ligated larvae Lp lipid content increased when ligation was performed on day 1 or 2, but not on day 3. So, different responses to starvation can be observed depending on the developmental phase of the same larval instar.     

Effects of the timing of initial feeding on growth and survival of spotted mandarin fish Siniperca scherzeri larvae

The effects of delayed first feeding on growth and survival of spotted mandarin fish Siniperca scherzeri larvae were examined under controlled conditions. Morphometric characters [yolk‐sac volume, oil globule volume, head depth (H_D), body depth (B_D), eye diameter (E_D), musculature height (M_H), mouth diameter (M_D) and total length (L_T)], body mass (M), specific growth rate (S_GR) and survival were evaluated under different first‐feeding time (2, 3, 4 and 5 days after hatching). Larvae began to feed exogenously at 2 days after hatching (DAH) and the point of no return (P_NR) occurred between 5 and 6 DAH at 23° C, range ±1·0° C. The yolk volume of larvae first‐fed at 2 days had a significant difference compared with that of larvae first‐fed at 3, 4 and 5 days on 3 and 4 DAH. The larvae first‐fed at 2 days achieved comparatively better growth performance than that of 3, 4 and 5 days. On 5 DAH, all morphometric characters had significant differences between 2 and 5 days and 2 and 4 days initial feeding, respectively. Total mortality was recorded on 9 DAH for the larvae first‐fed at 5 days. On 12 DAH, significant differences were observed between 2 and 4 days and 3 and 4 days initial feeding for all morphometric characters. From 16 DAH to the end of experiment, all growth variables of the larvae first‐fed at 2 days were significantly higher than those in other treatments. The S_GR (2–9 DAH) first‐fed at 2 and 3 days were significantly higher than 4 and 5 day treatments, and the S_GR (9–16 DAH) first‐fed at 2 days was significantly higher than 3 and 4 day treatments. There was no significant difference, however, of S_GR (16–28 DAH) among treatments. Survival rate was significantly higher at 2 days initial feeding (27·42%) when compared with 3 (15·96%) and 4 days (7·92%) initial feeding at the end of experiment. The present study suggests that the first feeding of S. scherzeri larvae should be initiated at 2 days after hatching for achieving good growth and survival.     

Response of fed and starved roach, Rutilus rutilus, to sublethal copper contamination

Fed and starved yearling roach, Rutilus rutilus . were subjected to a sublethal copper contamination of 80 μg Cu × l⁻¹ for 7 days. Copper accumulation was determined by atomic absorption spectroscopy. In both fed and starved fishes, the gill tissues showed significant uptake of copper, while the liver tissues of only starved specimens showed significant accumulation. Refeeding roach after 7 days of starvation and contamination resulted in a significant decrease of liver copper content. No copper release from the liver occurred if, after cessation of exposure, starvation was continued. Analysis of liver ultrastructure demonstrated no pathological lesions or copperspecific alterations. Cellular changes represented combined influences of nutrition and of copper. Qualitative as well as quantitative results provide evidence that the nutritional status of a fish is of great importance in modifying its response to sublethal copper contamination.     

Starvation reduces the heat shock protein responses in white sturgeon larvae

This study investigates the responses of white sturgeon larvae (Acipenser transmontanus) to starvation and thermal stress, through the measurement of nutritional status (i.e. growth performances) and cellular biomarkers: heat shock proteins (Hsp) 70 and 90. White sturgeon larvae (25 day post hatch; initial weight 179.0 ± 5.1 mg) were fed (20% body weight per day) or starved for 24, 48 or 72 hrs. Every 24 hrs, five larvae from each of the starved or fed treatment replicates were exposed to heat shock resulting from an increase in water temperature from 19°C to 26°C, at a rate of 1°C per 15 min, and maintained at 26°C for 4 hrs. No mortality was observed in this study. Starvation significantly (p < 0.05) decreased the body weight and body contents of energy, protein, and lipid of the experimental larvae, compared to the fed larvae. Heat shock induced the expressions of Hsp70 and Hsp90 in both the fed and starved group; however, starvation reduced the induction at all sampling points. The current study demonstrates that poor larval nutritional status, assessed by the aforementioned parameters, reduced heat shock responses to thermal stress, as measured by heat shock protein levels. Furthermore, Hsp70 and 90 are more sensitive to heat shock and starvation, respectively. This may be, in part, a result of the different functioning of the heat shock proteins in cellular stress response and warrants further study.     

Influence of delayed metamorphosis on postsettlement survival and growth in the sipunculan Apionsoma misakianum

Abstract. Certain stresses experienced by marine larvae from many groups can dramatically reduce aspects of juvenile performance. This study reports the effects of delayed metamorphosis and nutritional stress on survival and growth of the deposit-feeding sipunculan Apionsoma (= Golfingia ) misakianum . Approximately 600 larvae collected from the Florida Current plankton were distributed among 3 treatment groups. Ninety larvae (controls) were offered sediment and adult-conditioned seawater 4 d after collection, to induce metamorphosis; larvae of this species could not be induced to metamorphose by increasing the K⁺ concentration of seawater. The remaining 500 larvae were kept swimming for either 2 or 4 weeks, with or without phyto-plankton (clone T-ISO). At the end of the periods of prolonged larval swimming, subsampled larvae (360) were induced to metamorphose as in the controls. Surviving individuals were retrieved 6 weeks after the addition of excess sediment in all treatments, and weighed to document growth. Neither delayed metamorphosis nor starvation influenced juvenile survival. However, starving larvae for 2 weeks significantly reduced mean juvenile growth rates relative to the mean growth rate of control individuals (p<0.0001), while prolonging larval life by 4 weeks significantly reduced mean juvenile growth rates (p<0.05) whether or not larvae were fed. Reduced juvenile growth rates may have been caused by nutritional stress experienced by larvae in both the starved and fed treatments. The rapid response of freshly collected larvae to sediment indicates that competent larvae of this species routinely delay metamorphosis in the field. The extent to which they also experience food limitation is not yet clear. If competent larvae are food limited while delaying metamorphosis in the field, our results suggest that juveniles will grow more slowly and may thus exhibit reduced fitness.     

Satiation meal and the effects of meal and body sizes on gastric evacuation rate in brook trout Salvelinus fontinalis fed commercial pellets

Gastric evacuation (GE) experiments were performed on brook trout Salvelinus fontinalis fed commercial food pellets. The experiments included small fish (36 g; 15 cm total length, L_T) fed meals of 0·2, 0·4 and 0·8 g and large fish (152 g; 23 cm) fed meals of 0·8, 2·0 and 4·0 g at temperatures ranging from 15·1 to 18·2° C. The stomach contents were thereafter sampled and weighed at 3 h intervals until the first empty stomach was observed. The course of GE was examined by use of a general power function of the data that revealed that the square‐root function described the GE rate (GER) by the current stomach content mass independently of original meal size. Using the square‐root function, the relationship between GER and fish size was described by a power function of fish length, whereas the effect of temperature was described by a simple exponential function. GER of the commercial pellets fed to S. fontinalis could thus be described by (g h^?1), where S_t is stomach mass (g) at time t (h), L is total fish length (cm) and T is temperature (° C). The result of this study should provide a useful tool for planning of feeding regimes in production of S. fontinalis by optimizing growth and minimizing food waste.