Depth equilibration of a shallow-water cichlid fish

The cichlid Melanochromis exasperatus has a natural distribution which is restricted to a single island in Lake Malawi, Africa. Diving observations indicated that it does not occur below 4.5 m depth. Measurements of depth equilibration in a pressure tank showed that males can equilibrate to a depth of 25 m and females to 18 m. Mean maximum sustained rate of depth equilibration was 2 m day⁻¹. M. exasperatus survived a pressure decrease of 40% every 12 h from the maximum equilibration depth to the surface. The fish swim actively during the day but rest on the bottom at night when they are equilibrated to a depth 1 m deeper than ambient. Reduced activity at night is reflected in a drop in oxygen consumption to nearly half of the daytime active value.     

Lacustrine growth of juvenile pink salmon and a comparison with sympatric sockeye salmon

The growth rates of naturally sympatric juvenile pink Oncorhynchus gorbuscha and sockeye Oncorhynchus nerka salmon were compared in a common lacustrine environment in south‐west Alsaka, an unusual opportunity given the normal disparity in freshwater residence time of these two species. Fork length ( L _F) frequency distributions of juvenile pink salmon caught in the lake during the summer in 1991 and 1999–2003 indicated a growth rate of 0·54 mm day⁻¹, 54% greater than the estimated growth rate of juvenile sockeye salmon sampled from 1958 to 2003 (0·35 mm day⁻¹). Examination of daily growth rings on otoliths indicated that pink salmon in Lake Aleknagik grew an average of 1·34 mm day⁻¹ in 2003 but sockeye salmon grew only 0·63 mm day⁻¹(average specific growth rates were 3·0 and 1·8% day⁻¹, respectively). Pink salmon increased from c . 32 mm L _F and 0·2 g at emergence to 78 mm L _F and 3·0 g within 3–4 weeks. After experiencing these rapid growth rates, the pink salmon appeared to leave the lake by late July in most years. The diets of pink and sockeye salmon in the littoral zone of the lake were very similar; >80% of the stomach contents consisted of adult and pupal insects and the remainder was zooplankton. This high degree of diet overlap suggested that the observed differences in growth rate were not attributable to variation in prey composition.     

Digestion rate, gut passage time and absorption efficiency in the Antarctic spiny plunderfish

The absolute gut evacuation rate (GER) (g day⁻¹) of Harpagifer antarcticus increased with increasing ration mass, fish mass only influenced the absolute GER at a daily ration level of 0·3% wet fish mass (approximately a maintenance ration). The relative GER (% of meal fed day⁻¹) was also affected differently by fish and ration mass depending on the relative ration level being fed; at rations of 0·7% wet fish mass or above the relative GER decreased with increasing fish or ration mass (in such a way that the absolute GER remained constant and unaffected by fish mass). At maintenance (0·3% wet fish mass) rations the relative GER was not affected by fish size or ration mass. Thus, there appears to be a ration threshold above which the digestion physiology alters. Mass-specific GER (% g fish⁻¹ day⁻¹) decreased with increasing fish mass. Within a set relative ration level (% wet fish mass) an increase in fish mass decreased the mass-specific GER. At a fixed ration mass, an increase in fish mass (i.e. a reduction in the ration expressed as % fish mass) resulted in a decrease in mass-specific GER. Gut evaluation time (GET) decreased and absorption efficiency (A) increased with increasing absolute GER. The effect of ration and fish mass on the absolute and relative GER followed the same pattern irrespective of the diet, however the A and GER (% day⁻¹ and g day⁻¹) were higher and the GET shorter when the fish were fed shelled krill rather than amphipods.     

Effect of ration size on growth and gross conversion efficiency of young lemon sharks, Negaprion brevirostris

Young lemon sharks, Negaprion brevirostris , were kept under controlled conditions in an aquarium and fed blue runner, Caranx crysos , at different ration levels. The relationship between feeding rate and growth rate was best described by a von Bertalanffy growth curve, which predicted a maximum growth rate of 140 kJ kg⁻¹ day⁻¹ (0·66% b.w. day⁻¹), a maintenance ration of 199 kJ kg⁻¹ day⁻¹ (1·06% b.w. day⁻¹), and losses due to starvation of -236kJ kg⁻¹ day⁻¹ (1·11% b.w. day⁻¹). The relationship between gross conversion efficiency ( K ₁) and feeding rate was also examined. K₁ ranged from - 64 to 25% and did not drop at high ration levels. Activity levels of both starved sharks and sharks fed at maintenance were not significantly different (0·2 body lengths s⁻¹). K ₁ values generated from both laboratory and field data suggest that young lemon sharks can convert food to new tissue as efficiently as teleosts.     

Influence of different rations and water temperatures on the growth rates of shortfinned eels and longfinned eels

Juvenile (12–152 g) shortfinned eels Anguilla australis and longfinned eels A. dieffenbachia caught in New Zealand streams were fed squid mantle Nototodarus spp. 4 days per week in laboratory experiments. A linear multiple regression equation showed the amount of food eaten (0–2·7% w day⁻¹) explained 77·7% of the variation in specific growth rates (–0·60 to +1·07% w day⁻¹) among individual eels, while previous growth rates, water temperature (10·0–20·6°C), and eel weight (12–152 g) explained a further 5·6, 1·4 and 0·8%, respectively. Growth in length ranged from –0·3 to +0·9 mm day⁻¹. Eels which were starved and then given high rations grew substantially faster than expected. Once growth rates were adjusted for differences in ration and other factors, there were no significant differences in growth rates between species or individual fish. Growth of shortfinned eels fed maximum rations of commercial eel food depended on fish size and water temperatures and ceased below 9·0°C. Growth rates in the wild were substantially less than the maximum possible, after seasonal changes in water temperatures were taken into account, indicating that food supplies and not low water temperatures were controlling growth rates in the wild.     

Comparison of growth rate and formation of otolith increments in age-0 red snapper

For wild red snapper Lutjanus campechanus , mean otolith increment deposition rate after marking with oxytetracycline dihydrate (OTC) was daily (0.97 increments day⁻¹) when growth rates were fast (0.63 mm fork length, L _F day⁻¹), but were not daily (0.82 increments day⁻¹) when somatic growth was slow (0.2 mm L _F day⁻¹). For reared larvae ( n =8), increment deposition rates were daily (0.99–1.03 increments day⁻¹), and growth rates ranged from 0.6 to 0.9 mm L _F day⁻¹. Growth rate affected increment deposition rate as a threshold function, i.e. when growth rate was <0.3 mm L _F day⁻¹, deposition was less than daily, but above this level increment deposition did not exceed a daily rate. As growth rates increased increment widths increased. Examination of a sub-sample ( n =8) of the otoliths from the slowest growing wild fish by scanning electron microscopy did not increase increment counts. Because L. campechanus are late spring-early summer spawners, young fish can expect maximum growth due to warm summer temperatures. Thus, daily ageing methods should be well suited to this species.     

Reproductive migration of brown trout in a small Norwegian river studied by telemetry

The movement of 34 large (39–73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m³ s⁻¹) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m³ s⁻¹) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low ( c . 6° C), but not at high ( c . 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2–51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day⁻¹, respectively. All tagged brown trout that survived spawning returned to the lake after spawning.     

The effect of temperature and fish size on growth and feed efficiency ratio of juvenile spotted wolffish Anarhichas minor

The growth properties of juvenile spotted wolffish Anarhichas minor reared at 4, 6, 8 and 12° C, and a group reared under 'temperature steps', (T‐step) i.e . with temperature reduced successively from 12 to 9 and 6° C were investigated. Growth rate and feed efficiency ration was significantly influenced by temperature and fish size. Overall growth rate was highest at 6° C (0·68% day⁻¹) and lowest at 12° C (0·48% day⁻¹), while the 4 and 8° C, and the T‐step groups had similar overall growth rates, i.e . 0·59, 0·62 and 0·51% day⁻¹ respectively. Optimal temperature for growth ( T _{opt G} ) and feed efficiency ratio (T_{opt FCE}) decreased as fish size increased, indicating an ontogenetic reduction in T _{opt G} and T _{opt FCE}. The results suggest a T _{opt G} of juvenile spotted wolffish in the size range 135–380 g, dropping from 7·9° C for 130–135 g to 6·6° C for 360–380 g juveniles. The T _{opt FCE} dropped from 7·4° C for 120–150 g to 6·5° C for 300–380 g juveniles. A wider parabolic regression curve between growth, feed efficiency ratio and temperature as fish size increased, may indicate increased temperature tolerance with size. Individual growth rates varied greatly at all time periods within the experimental temperatures, but at the same time significant size rank correlations were maintained and this may indicate stable size hierarchies in juvenile spotted wolffish.     

Growth and physiological changes during metamorphosis of Senegal sole reared in the laboratory

The metamorphosis of Solea senegalensis was studied in larvae reared at 20° C and fed four different feeding regimes. A, Artemia (4 nauplii ml⁻¹); B, Artemia (2 nauplii ml⁻¹); C, mixed diet (2 nauplii ml⁻¹ and 3 mg ml⁻¹ microencapsulated diet); and D, microencapsulated diet (3·7 mg ml⁻¹). Rotifers were also supplied in all cases during the first days of feeding. These feeding regimes supported different growth rates during the pre-metamorphosis period (regime A, G=0·376 day⁻¹; regime B, G=0·253 day⁻¹; regime C, G=0·254 day⁻¹; regime D, G=0·162 day⁻¹). Larvae started metamorphosis 9 days after hatching (DAH) when fed the regime A, 13 DAH with regime B, 11 DAH with regime C and 15 DAH with regime D. A minimum 5·6–5·9 mm L_T was required under all feeding regimes to initiate the metamorphosis. Eye translocation was completed when the larvae reached 8·6–8·7 mm L_T (regimes A, B and C), but only 7·3 mm L_T with regime D. 4·4–6·2 days were required to complete eye migration under the regimes A, B and C, and 18·3 days under the regime D. This transformation is concomitant with changes in body reserves, and with the pattern of some digestive enzymes.     

Evidence of differences in growth and food intake regulation in different genetic strains of channel catfish

Norris and USDA-103 strains of channel catfish Ictalurus punctatus were compared for growth rate and food conversion ratio under satiation feeding and restricted feeding (1% body weight day⁻¹) regimes. At the start of the experiment Norris fish weighed 2·8 g, USDA-103 fish weighed 14·0 g. Therefore, a regression of the loge of specific growth rate against the log_e of mean body size with an empirically derived fixed slope of -0·37 was used to compare growth rates. Under both feeding regimes the USDA-103 strain had faster specific growth rates and more efficient food conversion. In subsequent studies, voluntary food intake of size matched fish (60 g average) from these two strains was compared using a radiographic method. Fish were acclimatized to tank conditions for 3 weeks prior to voluntary food intake measurement. Half of the groups were deprived of food for 2 days prior to food intake measurement, while the remaining groups were fed 1% body weight day⁻¹. The USDA-103 strain fish ate significantly more food and grew faster than the Norris strain fish. Previously fasted Norris fish subsequently ate more than their fed counterparts, whereas the fed USDA-103 fish consumed more food than the fasted USDA-103 group. When the USDA-103 strain fish were deprived of food for 4 , 2 or 0 days, all groups subsequently consumed between 4·5 and 5·0% of body weight in one meal. The USDA-103 fish, unlike the Norris fish were not stimulated to consume more after short-duration fasting. Taken together, these results suggest that there are genetic differences in growth, food conversion ratio and regulation of food intake between Norris and USDA-103 strains.     

Feeding and growth of early juvenile Japanese sardines in the Pacific waters off central Japan

Larval and early juvenile growth was backcalculated for individual Japanese sardines Sardinops melanostictus using the biological intercept method based on the allometric relationship between otolith radii and fish lengths. Sardines grew at 0·81 mm day⁻¹ during the larval stage. In the early juvenile stage, they grew from 32·3 to 45·4 mm fork length ( L ) over a 20-day period (0·64mm day⁻¹). Using the observed relationship between L and wet body weight ( W ), W = 0·00942 L ^2.99, W of the sardine juveniles was calculated to increase from 306 to 832 mg during the 20-day period. The carbon (C) requirement to achieve this growth in weight was estimated to increase from 5·7 to 9·6 mg day⁻¹. Stomach contents of the sardines were composed mostly of copepods (73%) and larvaceans (25%). Wet stomach content weight ( W_s ) was expressed by a power function of the W , W_s=0·731 W ^0·658. Carbon and nitrogen constituted 41·7 ± 1·5 and 10·0 ± 0·4% of the dry W_s , respectively. Stomach C content increased from 2·0 to 3·9 mg during the 20-day period. Three to four cycles of the daily turnover of stomach contents during the 16 h of daytime, corresponding to a gastric evacuation rate of 0·2–0·3 h⁻¹ under continuous feeding, met the C requirement to achieve the backcalculated growth in early juvenile sardines. The Kuroshio frontal waters seem to provide Japanese sardine juveniles with favourable growth conditions.     

Protein synthesis, nitrogen excretion and long-term growth of juvenile Pleuronectes flesus

This study aimed to measure protein synthesis using a stable isotope method, investigate protein-nitrogen flux in a flatfish Pleuronectes flesus , and use the data to test the hypothesis that individual differences in growth efficiency were related to individual differences in protein-nitrogen flux mediated through differences in protein synthesis and degradation. Three measurements of protein-nitrogen flux via consumption, protein synthesis and nitrogenous excretion were made for individual flounder during a 212-day period and fractional rates of protein-nitrogen flux were scaled for a 50–g flounder to provide mean values for protein consumption (2·11 ± 0·21% day⁻¹), protein synthesis (2·08±0·23% day⁻¹), protein growth (0·71±0·06% day⁻¹) and protein degradation (1·37±0·24% day⁻¹). Mean rates of nitrogenous excretion were 0·142 mg N g⁻¹ day⁻¹ and 0·047 mg N g⁻¹ day⁻¹ for ammonia and urea, respectively. Individual flounder had different protein growth efficiencies and this was correlated negatively and significantly with mean rates of protein synthesis ( r - 0·70; P <0·05) and degradation ( r - 0·67; P < 0·05) and correlated positively and significantly with the efficiency of retaining synthesized protein ( r +0·63, P <0·05). This supported the proposed hypothesis that flounder which grow more efficiently achieve this through adopting a low protein turnover strategy.     

Comparison of field-based and indirect estimates of daily food consumption in larval perch and zander

Since bioenergetics models for 0+ fish have seldom been validated by field consumption estimates, field-based and indirectly estimated daily food rations were compared in larval perch Perca fluviatilis and zander Stizostedion lucioperca. Field-based estimates were calculated with linear and exponential evacuation rates based on gut fullness data during a 24-h cycle, with hourly field samplings instead of the normally recommended 3-h intervals. Indirect calculations used bioenergetics modelling with variable activity multipliers ( A ). Field-based estimates of daily rations ranged between 0·21 and 0·27 g g⁻¹ day⁻¹ in perch (mean L _T 13·1 mm) and 0·31–0·40 g g⁻¹ day⁻¹ in zander (mean L _T 10·6 mm). The higher values were calculated by using the exponential model. Daily rations calculated by bioenergetics modelling with A = 1 were only slightly higher than direct estimates in both species. However, if A values >1 were used, calculated daily rations were substantially higher than direct estimates. Estimates of daily ration based only on every third value ranged between 41 and 72% compared with 1-h intervals, mainly because of lower estimates of evacuation rate.     

Microsatellite data reveals weak population substructuring in Copadichromis sp.'virginalis kajose', a demersal cichlid from Lake Malawi, Africa

Small but significant differences were found in allele frequencies among five populations (overall F _ST estimate (θ)=0·004, P=0·006; overall R _ST estimate (RHO)=0·019, P <0·00001) of the demersal cichlid Copadichromis sp.'virginalis kajose', collected from five locations in Lake Malawi. Pairwise F _ST estimates revealed significant differences between the most southerly population (Cape Maclear), and the three most northerly populations (Mbamba Bay, Metangula and Chilola). Pairwise R _ST estimates also revealed significant differences between some populations, but no geographical pattern was discernible. There was no evidence of isolation by distance using either the shortest straight-line distance between samples, or the distance around the shoreline following a 50 m depth contour. F _ST estimates were considerably lower than found in previous studies on the mbuna (rock-dwelling species), but higher than those found in a study of three pelagic cichlid species from Lake Malawi. Substructuring in C. sp.'virginalis kajose' appears to be on a similar scale to the Atlantic cod.     

Seasonal variability in growth of larval Japanese anchovy Engraulis japonicus driven by fluctuations in sea temperature in the Kii Channel, Japan

Seasonal variability in the growth of larval Japanese anchovy Engraulis japonicus was examined through otolith microstructure analysis based on the samples collected from the northern side (inner area, IA) and the southern side (outer area, OA) of the Kii Channel from April 2006 to March 2007. Growth trajectories (otolith backcalculated mean standard length of 5 day intervals from 5 days after hatch to 24 days) as well as the most recent 5 day mean growth rate of larvae before capture ( G ₅) differed among months. Growth trajectories showed the same pattern as G ₅. In IA, mean ± s.d. G ₅ ranged from 0·31 ± 0·04 mm day⁻¹ (January) to 0·73 ± 0·06 mm day⁻¹ (October). In OA, mean ± s.d. G ₅ ranged from 0·36 ± 0·05 mm day⁻¹ (January) to 0·79 ± 0·11 mm day⁻¹ (August). G ₅ values declined from November to January and then started to increase. In general, the seasonal patterns of growth were similar between IA and OA, and a clear seasonal pattern in growth was identified. When the relationships among larval growth rate, sea temperature, zooplankton density and larval density were examined, growth rate was positively related with sea temperature in both areas and not related with the other factors. The similar pattern in growth observed between IA and OA was probably due to the low spatial variability in sea temperature compared to its seasonal variability.     

Hydroacoustic measurement of swimming speed of North Sea saithe in the field

Saithe Pollachius virens , tracked diurnally with a split-beam echosounder, showed no relationship between size and swimming speed. The average and the median swimming speeds were 1·05 m s⁻¹(±0·09 m s⁻¹) and 0·93 m s⁻¹, respectively. However, ping-to-ping speeds up to 3·34 m s⁻¹ were measured for 25–29 cm fish, whose swimming speeds were significantly higher at night (1·08 m s⁻¹) than during the day (0·72 m s⁻¹). The high average swimming speed could be related to the foraging or streaming part of the population and not to potential weakness of the methodology. However, the uncertainty of target location increased with depth and resulted in calculated average swimming speeds of 0·15 m s⁻¹ even for a stationary target. With increasing swimming speed the average error decreased to 0 m s⁻¹ for speeds >0·34 m s⁻¹. Species identity was verified by trawling in a pelagic layer and on the bottom.     

The interaction of temperature and fish size on growth of juvenile halibut

Growth rate of individually tagged juvenile halibut was influenced significantly by the interaction of temperature and fish size. The results suggest an optimum temperature for growth of juvenile halibut in the size range 5–70 g between 12 and 15° C. Overall growth rate was highest at 13° C (1·62% day ⁻¹). At c. 5 g at the beginning of the experiment, fish at 16° C had the highest growth rate (3·2% day ⁻¹), but reduced this rate as they grew bigger. At 9 and 11°p C, growth rates were equal or only slightly lower during the later stages of the experiment, while the fish at 6° C showed significantly lower overall growth rate (0·87% day⁻¹). Optimal temperature for growth decreased rapidly with increasing size, indicating an ontogenetic reduction in optimum temperature for growth. Moreover, a more flattened parabolic regression curve between growth and temperature as size increased indicated reduced temperature dependence with size. Although individual growth rates varied significantly at all times within the experimental temperatures, significant size rank correlations were maintained during the experiment. This indicated an early establishment of a stable size hierarchy within the fish groups. Haematocrit was highest at the highest temperature while Na⁺/K⁺-ATPase activity was inversely related to temperature. There was no difference in plasma Na⁺, Cl⁻ and K⁺ concentrations among the temperature groups.     

Effect of acute and chronic ammonia and nitrite exposure on oxygen consumption and growth of juvenile big bellied seahorse

Juvenile big bellied seahorse Hippocampus abdominalis were exposed acutely and chronically to elevated ammonia and nitrite {24 h exposure: 0·01, 5·0, 10·1, 14·8 and 19·9 mg l⁻¹ total ammonia-nitrogen [TA-N] and <0·001, 74·4, 99·2 and 123·6 mg l⁻¹ [NO₂-N] nitrite-nitrogen and 35 days exposure: 0·11, 0·55, 1·67 and 3·07 mg l⁻¹ TAN and <0·001, 0·92, 4·67 and 9·10 mg NO₂-N l⁻¹}. Significant ( P <0·001) increases in oxygen consumption rate and ventilation frequency occurred at 14·8, 19·9 mg l⁻¹ TA-N and 99·2, 123·6 mg l⁻¹ NO₂-N for acutely exposed fish. Oxygen consumption rate was significantly ( P <0·05) elevated at 1·67 and 3·07 mg l⁻¹ TA-N in chronically treated fish and ventilation frequency increased significantly ( P <0·05) at 0·55, 1·67, 3·07 mg l⁻¹ TA-N and 4·59, 9·10 mg l⁻¹ NO₂-N. There were no significant differences in growth between controls and ammonia exposed fish. Mortalities occurred at 14·8, 19·9 mg l⁻¹ TA-N.     

Determining patterns of use by black bream Acanthopagrus butcheri (Munro, 1949) of re-established habitat in a south-eastern Australian estuary

Acoustic telemetry was used to assess patterns of utilization by black bream Acanthopagrus butcheri of regions with and without re-introduced large woody debris (LWD) in two estuaries of south-eastern Australia, the Mitchell and Tambo Rivers. The fish ( n = 46) were implanted with acoustic transmitters in December 2004 and March 2005 and monitored for c. 12 months. The two principal metrics from the telemetry data, number of visits per day ( N day⁻¹) and residency (amount of time, s) were highly correlated ( r > 0·948), and subsequent analyses were based on N day⁻¹. Rates of N day⁻¹ varied inconsistently among estuarine regions across diel periods and times of year for each river. In the Tambo River during autumn, winter and spring, the N day⁻¹ was greatest in the middle and upper estuarine regions during the day, and often greater in the lower region at dawn and dusk, but varied little among regions in summer. The provision of LWD had little effect on N day⁻¹ in the Tambo River. In the Mitchell River, N day⁻¹ varied little among estuarine regions without LWD, regardless of the time of day, and these patterns were consistent across seasons, but N day⁻¹ was significantly greater to the LWD during the day in winter and spring. Freshwater flows had little effect on monthly patterns of N day⁻¹ among regions in either estuary. The perceived 'benefits' to A. butcheri of re-establishing LWD within estuarine systems of south-eastern Australia depended strongly on the time of year, time of day and river system, but acoustic telemetry was a useful method of evaluating the use by fish of these artificial structures.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.