Temperature effects on otolith pattern formation in Atlantic cod Gadus morhua

The effect of food intake and temperature on otolith macrostructure and microstructure was examined experimentally in Atlantic cod Gadus morhua. Daily increment formation was validated and otolith accretion rate and optical density quantified using image analysis. Two‐week periods of starvation had no discernable effect on otolith increment width or optical density, despite having negative effects on somatic growth. In contrast, temperature had a strong positive effect on otolith accretion rate and clear effects on optical density with the otolith becoming more translucent at higher temperatures. Somatic growth, otolith accretion and otolith optical density each had a significantly different response curve to temperature. No relationship was detected between individual somatic growth rates and the accretion rate or optical properties of the otolith. The experimental manipulation of temperature‐induced otolith patterns similar to the ‘false ring’ secondary structures sometimes observed in the otoliths of wild fish. The results suggest that otolith pattern arises from a combination of temperature and seasonal effects, but not directly from individual variation in somatic growth.     

Growth estimates from otolith increment widths of juvenile chinook salmon (Oncorhynchus tshawytscha) reared in changing environments

For otolith increments to provide useful estimates of fish growth, otolith growth must covary closely with somatic growth. We reared groups of juvenile chinook salmon ( Oncorhynchus tshawytscha Walbaum) for 70 days, changing ration or temperature during a 20-day treatment period. Restricted rations halted somatic growth, however increment widths decreased gradually; somatic growth was overestimated from increment width. Otolith growth followed changes in water temperature more closely than changes in ration, supporting a hypothesized effect of metabolic rate on otolith growth. Increment growth was only loosely coupled to fish growth rate, and may also be affected by past growth histories. For juvenile fish, increment widths may not be sensitive indicators of short-term changes in growing conditions.     

Otolith accretion rates: Does size really matter?

This study examined the relationship between otolith size and growth in juvenile cod (Gadus morhua L.). Two groups of juvenile cod were reared under different food ration and temperature regimes to obtain fish of similar somatic size but with different sized otoliths. The two groups were subjected to alternating temperature regimes and intermediate ration levels. Large otoliths grew significantly faster than the small ones and variation between individuals was extensive. The ratio of otolith growth during cold and warm temperature exposure did not differ between groups, and the observed growth pattern is therefore not attributable to differential growth within individual temperature periods. The ratio decreased with otolith size, presumably as a result of ontogenetic decrease in otolith protein composition. These results suggest that processes coupled to the metabolic rate of the endolymphatic epithelium are the key driver behind otolith growth.     

Effects of variable ration levels on direct and indirect measures of growth in juvenile red drum (Sciaenops ocellatus)

Relationships between somatic growth (length and weight) and two indirect measures of growth (otolith growth, RNA/DNA ratio) were assessed for red drum (Sciaenops ocellatus) under different feeding rations [0%, 2.5%, 5%, 10%, 15%, and 20% body weight (BW)/day] for 30 days. Representative samples from each ration level were taken in 10-day intervals between Day 0 and Day 30 for evaluation of direct and indirect growth measures. Positive correlations were observed between ration levels, somatic growth, and otolith growth. Statistical differences in weight and length of red drum were observed among ration levels by Days 10 and 20, respectively. Statistical differences for measures of otolith growth among ration levels were evident by Days 20 and 30. In addition, RNA/DNA ratios showed clear separation between fish that were starved and fish that were fed but demonstrated minimal separation among ration levels. Overall, the combination of a measure of somatic growth (weight) and a measure of otolith growth (otolith weight) resulted in the most statistical separation among ration levels. Findings from this study suggest that somatic growth, otolith growth and RNA/DNA ratios are suitable measures of relative growth of red drum; however, due to differences in sensitivity, caution must be exercised when using indirect growth (otolith growth, RNA/DNA ratios) measures to estimate recent growth.     

Otolith oxygen and carbon stable isotopes in wild and laboratory-reared plaice (Pleuronectes platessa)

The relationship between water temperature, growth rate, and otolith isotopic ratios was measured for juvenile plaice (Pleuronectes platessa) reared at two temperatures (11 and 17°C) and two feeding regimes (1 and 3 prey items·ml^?1). The otolith isotope ratios in individual fish ranged from ?2 to ?4 for carbon isotope ratios (δ¹³C) and from 0.2 to 1.9 for oxygen isotope ratios (δ¹⁸O). The otolith oxygen isotope ratios were significantly affected by water temperature, but not by feeding level, and there were no significant synergistic effects. The fractionation of oxygen isotopes during otolith growth was independent of individual growth rate. Carbon isotope ratios were not significantly affected by food ration or water temperature, but were related to fish growth rate. The carbon isotope ratios were negatively correlated with fish length in the colder water treatments, and tended to increase with fish length in the warm water treatments. The laboratory-determined relationship between otolith oxygen isotope ratio and water temperature was applied to individuals of five species (plaice, cod, whiting, haddock, gurnard) collected in a single trawl sample. The otolith derived temperatures often overestimated measured water temperatures. The difference between real and estimated water temperatures varied between species, and the closest fit was for field-caught plaice.     

Effects of temperature,starvation and photoperiod on otolith increments in larval Chinese sucker, <Emphasis Type="Italic">Myxocyprinus asiaticus</Emphasis>

Effects of water temperature, starvation and photoperiod on otolith increment formation in larval Chinese sucker, Myxocyprinus asiaticus, were examined in this study. The results demonstrated that otolith increments of larvae reared under diel temperature fluctuations were very clear and appeared with a high contrast, while those of larvae raised under constant water temperatures were vague or hard to identify. The increment deposition rates were less than 1.0/day in later stage of starvation period. Also, increment deposition was affected by cyclic regimes of water temperature fluctuations, the number of increments corresponded to the cycle times rather than the exact days larvae experienced. However, varying of feeding frequency and photoperiod did not result in any alterations of daily increment formation. Increment width increased obviously with higher rearing temperatures till several days after yolk absorption. However, the width presented an ontogenetic decline during period of endogenous nutrition and the first several days of exogenous nutrition stage. Starvation decoupled the relationship between somatic growth and otolith growth; otolith kept growing, and increment width of starved larvae was similar to those in fed individuals before 9–20 days old; the divergence of increment width from the fed larvae occurred in later stage of starvation period. It can be concluded that temperature regimes and food levels are the major factors affecting increment formation in terms of clarity, deposition rate and width, while photoperiod and feeding frequency have less influence on it.     

Energy allocation in juvenile sablefish: effects of temperature, ration and body size

The lipid deposition of juvenile sablefish Anoplopoma fimbria was examined, in particular, the changes in allocation over time. Growth rates of early juveniles (initial size 36–50 mm total length, L_T) were manipulated using two temperatures (10 and 20° C) and two rations (ad libitum and 3–4% body mass day^?1). Fish L_T, mass and lipid content were measured every 3 weeks for 15 weeks. Irrespective of treatment, the relationship of total lipid content with body size was clearly hyperallometric; small juveniles allocated relatively more energy to growth and less to lipid storage than large juveniles. After adjusting for the influence of body size, temperature and ration significantly influenced body composition but these effects varied over the course of the experiment. In the first 3 week time period, fish on the high ration, high temperature treatment had reduced lipid storage relative to other treatments, but in all subsequent time periods their lipid concentrations were similar to or higher than those of fish on other treatments. In contrast, fish held at low rations and low temperatures initially had average levels of lipid concentration, but after 6 weeks their levels were lower than other treatments. Estimation of allocation to lipid storage over time (proportion of dry mass increase comprised of lipid) suggested that fish in all of the treatments were approaching an asymptotic level of lipid concentration (c. 50–60% of dry mass) but with different rates of lipid increase. Within a treatment, it was predicted that individual differences in allocation would result in trade‐offs between somatic growth and storage. This trade‐off was evident only for fish held on low rations at low temperatures. In contrast, fish held on high rations at high temperatures exhibited the opposite pattern of a positive correlation between somatic growth and storage. These results suggest that lipostatic regulation of appetite is unlikely in juvenile sablefish. When resources are unlimited, this species appears to adopt a maximizing strategy for both somatic growth and lipid accumulation.     

Feeding and growth of juvenile sea bass: the effect of ration and temperature on growth rate and efficiency

The effect of ration on the growth of pairs of juvenile sea bass Dicentrarchus labrax fed squid mantle was recorded at four temperatures: 6, 10, 14 and 18) C, covering the range typical of Welsh coastal waters. Initial weight of the fish ranged from 2.8 to 15.9 g. A predictive model for the maximum meal size (M_max) at temperatures between 10 and 18) C, accounted for 95% of the variance in lnM_max. Even when offered excess food, bass at 6) C had a low rate of food consumption [0.19% body weight (BW) day^?1] and lost weight (G=?0.04% day^?1). Predictive regression models for specific growth rate (G) accounted for 86% of the variance at reduced rations and 70% at maximum meals. The relationship between G (calculated for total biomass per tank) and ration was a decelerating curve. G at maximum meals increased with temperature, at lower rations G decreased with temperature. For a pair of bass with a combined weight of 15 g, predicted maintenance ration ranged between 0.7 and 2.3% BW day^?1 and increased with temperature. Maximum meal size was more sensitive to temperature than maintenance ration. At 18) C optimum ration was 7.4% BW day^?1. At lower temperatures, the optimum ration was the maximum meal. The maximum gross growth efficiency was 17.4% at 18) C. Mean absorption efficiency was 94.8%. Ration level had no significant effect on absorption efficiency, which was lowest at 6) C. Condition indices (Fulton condition factor, wet and dry liver—somatic indices and body depth index) increased with meal size at all temperatures except 6) C. An increase in temperature between 10 and 18) C generally resulted in a decrease in condition indices at a given ration. When comparisons were made at a given standard length, gut and carcass weight increased with ration. Visceral fat and gut weight decreased with increased temperature.     

The effect of temperature and somatic growth on otolith growth: the discrepancy between two clupeid species from a similar environment

Otolith growth rates of the early life stages of herring Clupea harengus ( n = 472) and smelt Osmerus eperlanus ( n = 348) collected in the Vistula Lagoon (Baltic Sea) during 1997–1999 were analysed. The larvae and early juveniles were not only collected in the same geographical area they were also of the same size (range 15–43 mm standard length, L _S), similar ages and were collected during the same seasons (May to July). Although the two clupeid species experienced very similar environmental conditions, there were significant discrepancies in the analysed relationships. The otolith growth of larval and juvenile smelt was very strongly related to somatic growth while temperature had a minor effect. In herring, the effect of somatic growth, although clearly visible and statistically highly significant, was of less importance than temperature. Furthermore, variation in the otolith size and L _S relationship was affected by temperature and somatic growth in both species, but the variance of otolith size at L _S was higher for herring than for smelt. Although growth backcalculation from otoliths can presently be recommended as an appropriate method for use with both smelt and herring (despite possibly lower precision and accuracy with the latter), other methods referring directly to short-term increment width changes ( e.g. marginal increment analysis) are recommended for smelt but not for herring.     

Effects of temperature and ration level on the growth and food conversion efficiency of Salmo gairdneri, Richardson

The effects of temperature and ration size on the growth rate and gross efficiency of food conversion of juvenile rainbow trout Salmo gairdneri were evaluated during 25-day seasonal experiments. Rations ranged from near-starvation to repletion levels. Test temperatures were 3 and 6°C higher than the controls which fluctuated dielly and seasonally. At rations near maintenance, elevated temperatures decreased trout growth. As the feeding rate increased the detrimental effect of temperature on growth was ameliorated. At repletion feeding levels, elevated temperature up to 17°C improved trout growth by increasing the maximum food consumption rate. With a temperature increase from 6.9 to 22.5°C maintenance rations increased from 2.2 to 7.5 % body weight per day. Gross efficiency was dependent upon ration level and temperature. As the food consumption rate increased, efficiency increased to a maximum, then generally declined at repletion levels. Elevated temperatures resulted in reduced efficiencies at low consumption rates but temperatures had little effect at high ration levels. A field study provided estimates of the food consumption relationships established in the laboratory, suggested any substantial increase of stream temperature without a concomitant increase of food abundance would result in decreased trout production.     

Effects of starvation on the formation of daily growth increments in the otoliths of milkfish, Chanos chanos (Forsskål), larvae

The effects of starvation on daily growth and increment formation in the otolith were examined using a double oxytetracycline-labelling method on larval milkfish, Chanos chanos (Forsskål), reared under different feeding regimes. The results indicated that the differences in body and otolith growth between the larvae fed once and three times a day were not significant, and that the otolith growth increment was deposited daily in both groups of fed larvae. In contrast, the starved larvae grew at a slower rate than fed larvae in body length and otolith dimensions, and the otolith growth increment in the starved larvae was not deposited on a daily basis. After undergoing starvation, the larvae were unable to recover their normal growth either in otolith increment deposition or in body and otolith growth even though they were fed. Therefore, the application of ageing techniques based on counting otolith growth increments seems to be inaccurate for starved larvae.     

Effect of ration and body size on the energy budget of juvenile white sturgeon

Growth and energy budget were measured for three sizes (2.4, 11.1 and 22.5 g) of juvenile white sturgeon Acipenser transmontanus held at 18.5° C and fed tubificid worms at different levels ranging from starvation to ad libitum . For each size-class, specific growth rate increased linearly with increasing ration, and conversion efficiency was highest at the maximum ration. Growth rate decreased with increasing fish size at the maximum ration, but increased with size at each restricted ration. Conversion efficiency increased with increasing ration for each size-class and was usually highest at the maximum ration. Faecal production accounted for 3.2–5.2% of food energy. The proportion of food energy lost in nitrogenous excretion decreased with increasing ration. With increases in ration, the allocation of metabolizable energy to metabolism decreased, while that to growth increased. Fish size had no significant effect on the allocation of metabolizable energy to metabolism or growth. At the maximum ration, on average 64.9% of metabolizable energy was spent on metabolism, and 35.1% on growth.     

Bioenergetics of growth of a cyprinid, Phoxinus phoxinus (L.): the effect of ration and temperature on growth rate and efficiency

Growth of minnows, Phoxinus phoxinus , weighing 1-5.5 g was studied experimentally at five ration levels from starvation to ad libitum and four temperatures ranging from 5 to 15°C. The relationship between specific growth rate (SGR) and ration was a decelerating curve. SGR at maximum rations increased with increased temperature, but at restricted rations it decreased with increased temperature. Predictive models for the specific growth rates were developed using multiple regression. Maintenance rations and optimum rations both increased with increased temperature. Maintenance rations were less sensitive to temperature than optimum rations and mostly lay between 1 and 2% of body weight per day. Conversion efficiencies increased with increased ration from zero value at the maintenance ration to a peak at the optimum ration, then decreased with further increases in ration. At a given restricted ration level, conversion efficiencies generally decreased with increased temperature. At maximum rations, conversion efficiencies were relatively insensitive to temperature. Growth in wet weight, dry weight and energy content showed similar responses to ration, temperature and body weight.     

Effects of different food restrictions on somatic and otolith growth in Nile tilapia reared under controlled conditions

.Nile tilapia Oreochromis niloticus , initial age 12 days, were given an unrestricted (NR) or restricted (R) ration over 93 days which resulted in fish of very different sizes although the body condition factor ( K ) and the viscero-somatic index ( I _V) remained almost unchanged. In a second stage (64 days) each group (NR & R) was divided into three subgroups that were subjected to 0 (NR0, R0), 15 (NR15, R15) and 30 (NR30, R30) days of food restriction, respectively. The impact of the different treatments on the somatic growth during the second stage of the experiment had an effect, with a highly significant difference between the mean ± S.D. masses ( M _T) in the different subgroups (NR0= 115.0 ± 26.6 g; NR15 = 94.8 ± 24.9 g; NR30 = 56.3 ± 28 g; R0 = 76.4 ± 20.1 g; R15 = 72.l ± 17.6 g; R30 = 43.6 ± 17.2 g). Similarly, K and I _V decreased. Irrespective of the initial feeding condition, the width of the otolith microincrements started to decrease at the end of the first or second day of restricted feeding. In the subgroups given a restricted food ration for 30 days (NR30 and R30), this decrease reached a plateau at about day 30, which was maintained even when the restriction had ended. This slowed growth did not lead to any marked halt in microincrement formation, since there were no significant differences (ANOVA; P >0.05) in the numbers of increments counted in the various subgroups. The results show that in 153 day old fish, a period of severe food restriction, even if prolonged (15 to 30 days), had no influence on the timing of the laying down of microincrements but only affected their growth.     

Restricted fish feeding reduces cod otolith opacity

The purpose of this work was to examine the effect of reduced feeding and constant temperature on cod otolith opacity. Three groups of juvenile cod were given restricted food rations at different times for 4 months, resulting in depressed somatic growth. Otolith opacity was measured on pictures of the otolith sections. The otolith carbonate deposited during the experimental period was generally opaque compared to the more translucent otolith material deposited prior to and after the experimental period, when the fish were kept in a pond and in sea‐cages at higher temperatures. Large variations in otolith opacity were found between individual fish both within groups and between groups. In two of the three groups significantly more translucent otolith material was deposited in response to reduced feeding. Our results show that variations in feeding and hence fish growth resulted in variation in otolith opacity, but the effect was minor compared to that of variations in ambient temperature. The combined influence of these effects, which both act on fish metabolism, are most likely controlling the seasonal opacity changes observed in wild fish. Our results help explain the variations seen in fish at constant temperatures.     

The bioenergetics of the southern catfish (Silurus meridionalis Chen): growth rate as a function of ration level, body weight, and temperature

A feeding-growth experiment was conducted in the laboratory on 114 young southern catfish ( Silurus meridionalis Chen) with initial weights of 8.71–127.9g at 15, 20, 25 and 30°C. The experiment consisted of eight weight-temperature groups, with five ration levels ranging from starvation to satiation in each group. A multiple regression equation fitted to the experimental data was developed to describe the relation between specific growth rate (SGR) and the three factors, ration level (RL), body weight ( W ) and temperature ( T ): SGR = 0.471 + 0.172ln W −0.0443 T +0.0682 T ln(RL + l). This predicts that with increasing temperature the specific growth rate decreases at lower ration levels and increases at higher ration levels. The equation, SGR = a + b ln(RL + l), may be considered as the basic growth model where a is the maintenance metabolism exponent and b is the conversion exponent of the net energy; body weight and temperature influence the two parameters. With this relationship the two antagonistic effects of temperature on growth can be understood, increasing temperature imposes a negative effect on growth due to increment in energy cost for maintenance metabolism, and a positive effect due to higher efficiency of transforming food energy into net energy; the positive effect will increase at higher ration levels. This could also explain why at a restricted ration level relationships between growth and temperature are different in different species.     

Otolith increment widths and somatic growth rate: the presence of a time-lag

Populations of the estuarine glass fish, Ambassis vachelli Richardson, were used to study the relationship between somatic growth and widths of daily increments in the sagittal otoliths. Variations in the somatic growth of A. vachelli were induced by a series of experimental feeding regimes which included feeding to satiation with two food sources and a starvation treatment. After 33 days of exposure to the experimental feeding regimes significant differences in the mean wet weight of individuals amongst the feeding treatments were recorded. Fishes subject to a starvation treatment showed a significant reduction in wet weight compared to the pretreatment population and the two experimental feeding regimes. No changes in lengths of fishes were recorded.
Validation techniques revealed that daily increments were laid down in the sagittal and asteriscal otoliths. Estimates of ring widths from samples of sagittal otoliths revealed significant treatment effects. The increments of fishes from the starvation treatment showed a significant decline in mean increment width relative to the feeding treatments. This difference was detected only after a 15 day period of experimental feeding. It is suggested that the gradual decline in increment width reflects the exhaustion of readily mobilized energy reserves.     

Is the marginal otolith increment width a reliable recent growth index for larval and juvenile herring?

Marginal otolith increment width analysis was performed on field‐collected larval and juvenile spring‐spawned herring Clupea harengus that experienced variable feeding conditions and high temperatures that were above the optimum for growth. Although drastic zooplankton biomass reduction had a significant effect on increment width, a delay of a few days in the otolith response was observed. More importantly, a very clear, positive temperature effect on marginal increment width was demonstrated in fish characterized by temperature independent somatic growth. These results indicate that under natural conditions it may be impossible to distinguish increment width changes related to variation in feeding conditions from changes caused by temperature fluctuations. Therefore, it was concluded that marginal otolith increment width analysis could not be used as a recent growth index ( I _G) for herring larvae and juveniles exposed to drastic temperature fluctuations. The implication of these results is significant not only for the use of marginal increments as a recent growth index, but also if growth rate backcalculation is to be used as a research method.     

The effects of elevated summer temperature and sublethal pollutants (ammonia, low pH) on protein turnover in the gill and liver of rainbow trout (Oncorhynchus mykiss) on a limited food ration.

Protein synthesis, degradation and growth of the liver and gills were determined in juvenile rainbow trout (Oncorhynchus mykiss) fed a limited ration and exposed for 90 days to normal or elevated summer temperatures (+2 degrees above ambient) and either low pH (5.2) in softwater or 70 microM total ammonia in hardwater. The limited ration resulted in low rates of growth (< 0.80% per day) and protein synthesis in all fish. In softwater, whole-body growth was significantly inhibited by elevated temperature but stimulated by low pH, although tissue protein metabolism was generally unaffected by these treatments. There was no significant difference in final size between the groups of fish in hardwater, but liver protein synthesis and degradation were significantly lower at +2 degrees C, the reduction in synthesis being due to an inhibition of both the capacity for protein synthesis, Cs and the RNA translational efficiency, kRNA. Gill protein metabolism was unaffected by the experimental treatments in trout in hardwater. The authors conclude that a global warming scenario would be detrimental to protein synthesis and growth in freshwater fish under conditions of food limitation in summer, and when late summer temperatures approached the upper thermal limit of the species, regardless of food availability.     

Maternal dopamine exposure provides offspring starvation resistance in Daphnia

The neurotransmitter dopamine has been shown to play an important role in modulating behavioral, morphological, and life history responses to food abundance. However, costs of expressing high dopamine levels remain poorly studied and are essential for understanding the evolution of the dopamine system. Negative maternal effects on offspring size from enhanced maternal dopamine levels have previously been documented in Daphnia. Here, we tested whether this translates into fitness costs in terms of lower starvation resistance in offspring. We exposed Daphnia magna mothers to aqueous dopamine (2.3 or 0 mg/L for the control) at two food levels (ad libitum vs. 30% ad libitum) and recorded a range of maternal life history traits. The longevity of their offspring was then quantified in the absence of food. In both control and dopamine treatments, mothers that experienced restricted food ration had lower somatic growth rates and higher age at maturation. Maternal food restriction also resulted in production of larger offspring that had a superior starvation resistance compared to ad libitum groups. However, although dopamine exposed mothers produced smaller offspring than controls at restricted food ration, these smaller offspring survived longer under starvation. Hence, maternal dopamine exposure provided an improved offspring starvation resistance. We discuss the relative importance of proximate and ultimate causes for why D. magna may not evolve toward higher endogenous dopamine levels despite the fitness benefits this appears to have.