Effect of salinity and temperature on the growth of yearling Arctic cisco (Coregonus autumnalis) of the Alaskan Beaufort Sea

The growth of 1-year-old Arctic cisco ( Coregonus autumnalis ) was monitored under laboratory conditions for fish acclimated to one of two temperatures (5 and 10° C) and one of five salinities (6, 12, 18,24, 30‰). Fish were maintained for 43 days at rations of 3% wet body weight per day at 5° C and 5% wet body weight per day at 10° C, with rations adjusted for weight gain every 7–12 days. Fish increased 9–11% in length and 55–71% in weight at 5° C, and 23–27% in length and 141–161% in weight at 10° C. Length and weight increased linearly over 43 days. There was a statistically significant effect of temperature on growth but no statistically significant effect of salinity. Higher growth rates at 10° C were partially attributable to significantly greater gross conversion efficiency at the higher temperature. Over the course of the experiment, the condition (weight per unit length) of all fish increased by 3·2 to 63·6% at 5° C and by 5·6 to 46·0% at 10° C. There was no discernible effect of salinity on condition at either temperature. These results demonstrate that, with salinity acclimation and high food ration, 1-year-old Arctic cisco can grow at equivalent rates across salinities ranging from 6 to 30‰. The ecological implications of the results are discussed.     

Effect of body size, temperature, and salinity on the routine metabolism of larval and juvenile spotted seatrout

Routine oxygen consumption rates of young spotted seatrout Cynoscion nebulosus (Sciaenidae) were measured over a range of temperatures (24, 28, 30 and 32° C) and salinities (5, 10, 20, 35 and 45). Larvae and juveniles, 4·1–39·5 mm standard length ( L _S), ranging several orders of magnitude in dry body mass were used to estimate the mass–metabolism relationship. Oxygen consumption (μl O₂ larva⁻¹ h⁻¹) scaled isometrically with body mass for larvae <5·8 mm L _S(phase I, slope = 1·04) and allometrically thereafter (phase II, slope = 0·78). The inflection in the mass–metabolism relationship coincided with the formation of the hypural plate and an increase in the relative tail size of larvae. Salinity did not have a significant effect on routine metabolism during phase I. Temperature and salinity significantly affected routine metabolism during phase II of the mass–metabolism relationship. The effect of salinity was temperature dependent, and was significant only at 30° C. Response surfaces describing the environmental influences on routine metabolism were developed to provide a bioenergetic basis for modelling environmental constraints on growth.     

The effects of environmental factors on rainbow smelt Osmerus mordax embryos and larvae

Experiments were conducted to identify environmental factors that influence the survival of rainbow smelt Osmerus mordax during their early life stages. Developing rainbow smelt embryos and yolk-sac larvae were cultured under controlled conditions with different dissolved oxygen (DO; 1·09, 2·18, 4·37 and 6·55 mg l⁻¹, pH (4·0, 4·5, 5·0, 5·5, 6·0 and 7·0), nitrate ( 0·7, 3·6, 7·3, 14·6 and 29·2 mg l⁻¹), phosphate (0·04, 0·21, 0·42, 2·08 and 4·17 mg l⁻¹) and salinity (0, 5, 10, 15, 20 and 30) levels. Rainbow smelt embryos were also incubated with simulated tidal salinity fluctuations (2–28), ultraviolet radiation (irradiances of 2·8, 6·2 and 5·1 W m⁻²) and under natural conditions in two rainbow smelt spawning rivers. In the laboratory, hatch was only impaired under the lowest DO and pH conditions (0 and 13% hatch, respectively) and at highest constant salinity levels (0% hatch). Larval survival was only affected by pH levels ≤5·0. The experiment that compared hatch under natural conditions was terminated when embryos became covered with silt and fungus. These results suggest that water acidification, sediment and fungal growth may affect rainbow smelt survival during their early life stages.     

Effects of diet supplementation with carp ovary on gonad differentiation and growth of the European eel

Treating elvers of European eel Anguilla anguilla with mature carp ovary for 3–6 months during early growth induced female differentiation in 51·6–66·7% of treated animals compared with c . 5% in controls. The treatment also induced differentiation of ovaries in eels <13 cm L _T and a higher number of Syrski organs with ambisexual characters, and was most effective when administered at an early growth stage. The results could be attributed to the natural steroid content of the carp ovary. The total weight of treated animals at the end of the farm experiment was 84·7% higher than controls. The specific growth rate for weight was significantly higher in female yellow eels than in males, for both control and treated groups. The enhanced growth was related to induced feminization. A diet supplementation with mature carp ovary could be a good approach to control of sex differentiation and growth in eels.     

Feeding behaviour of yearling and older hybrid grass carp

Hybrid grass carp resulting from the cross of a female grass carp, Ctenopharyngodon idella (Val.), and a male bighead carp, Hypophthalmichthys ( Aristichthys ) nobilis Rich., 12–18 months old ( c . 300 mm T.L.) were studied in a two-part experiment to determine feeding preference and total daily consumption fish^-1 on selected species of aquatic plants. Fish were maintained in circular pools with 6840·8 1 of water inside a temperature-controlled greenhouse. Preference tests were conducted at three temperature ranges; 25–28° C, 17–20° C and 12–15° C. Based on the time to complete consumption or the relative quantity consumed, the most preferred plant was Lemna gibba when in combination with six other species. Chara sp., Najas guadalupensis and Potamogeton peciinatus were readily consumed and considered to be of about equal preference. Ceratophyllum demersum and Myriophyllum brasiliense were least preferred. Hybrid grass carp generally consumed as much plant material species^-1 and in the same order of preference at the 12–15°C range as they did at 25–28° C. In the second part, mean daily consumption (g) fish^-1 at 25·7–31·0° C for five plant species tested separately was as follows: Chara sp. 369·8; Lemna gibba 178·2; Najas guadalupensis 172·6; Hydrilla verticillata 106·4 and Ceratophyllum demersum 8·8.     

Microhabitat selection in the early juvenile mudskipper Boleophthalmus pectinirostris (L.)

Using laboratory choice experiments, behavioural preferences of the early juvenile mudskipper Boleophthalmus pectinirostris for temperature, salinity and sediment were observed. The temperature preference experiments were conducted in an annular chamber with a thermal gradient of 27 to 34° C, and the fish selected a mean ± s . d . temperature of 31·2 ± 0·5° C. The salinity preference experiments were conducted in an aquarium with decreasing salinity from 20 to 15, 10, 5 and 0·5, and significantly more ( P < 0·05) fish were found in water with a salinity of 5. The sediment preference experiments were tested in circular tanks which contained four types of sediment (medium sand, fine sand, muddy sand and sandy mud), and the fish showed a clear preference for sandy mud. These results indicated that early juvenile B. pectinirostris showed behavioural preference for microhabitats. Temperature and salinity probably set large-scale boundaries on distribution, but sediment should be a critical factor for determining the distribution of the mudskipper.     

Influence of water temperature and feeding regime on otolith growth in Anguilla japonica glass eels and elvers: does otolith growth cease at low temperatures?

The influences of water temperature and feeding regime on otolith growth in Anguilla japonica glass eels and elvers were investigated using individuals reared at 5, 10, 15, 20, 25 and 30° C and in fed or unfed conditions at salinity 32 after their otoliths were marked with alizarin complexone (ALC). To eliminate the difficulty of observing the edges of otoliths with optical (OM) or scanning electron (SEM) microscopes, three to 10 individuals were sampled from each tank at 10, 20 and 30 days during the experiment and reared for an additional 10 days at 25° C after their otoliths were marked a second time. Otolith growth and the number of increments were measured using both OM and SEM. Most A. japonica commenced feeding after 10 days at 20–30° C or after 20 days at 15° C, but no feeding occurred at 5 and 10° C. No otolith growth occurred at 5 and 10° C except in two individuals with minimal increment deposition at 10° C. Otolith growth was proportional to water temperature within 15–25° C and not different between 25 and 30° C. At 15, 25 and 30° C, the mean otolith growth rate in fed conditions was higher than in unfed conditions. The number of increments per day was significantly different among water temperatures (0·00–0·01 day⁻¹ at 5 and 10° C, 0·43–0·48 day⁻¹ at 15° C and 0·94–1·07 day⁻¹ at 20–30° C). These results indicated that otolith growth in A. japonica glass eels and elvers was affected by temperature and ceased at ≤10° C under experimental conditions. Hence, future studies analysing the otoliths of wild-caught A. japonica glass eels and elvers need to carefully consider the water temperatures potentially experienced by the juveniles in the wild.     

Influence of salinity on early development in the spined loach

Spined loach Cobitis taenia developed successfully between 0·12 and 4·80‰ salinity. At 6·00‰, net production was strongly reduced, and development failed at or above 7·20‰. Below 0·12‰ S, net production became variable, indicating restrictive effects. In comparison with other primary freshwater fish species C. taenia has a low sensitivity to salinity. The upper limit for early development was equal to the highest salinity under which C. taenia adults are found along the Baltic coast. Therefore, salinity should not limit early development within the brackish habitats of spined loach.     

The critical thermal limits for juvenile Arctic charr Salvelinus alpinus

The chief objective was to determine the critical thermal limits for alevins, fry and parr of Arctic charr, Salvelinus alpinus , (L.) from four races living in Windermere (northwest England). The experimental fish were reared in a hatchery but were the progeny of wild parents. As comparisons between tethal temperatures at four acclimation temperatures (5, 10, 15, 20° C) revealed few significant racial differences, the data were pooled to estimate the lethal values for survival over 7 days (incipient lethal temperature) and over only 10 min (ultimate lethal temperature) for each life stage. Upper lethal values increased with acclimation temperatures for alevins but this effect was negligible for fry and parr, Alevins were generally less tolerant than fry and parr at lower, but not higher, acclimation temperatures; e.g. after acclimation at 5° C, mean upper ultimate values were 23·3, 25·1 and 25·7° C and mean upper incipient values were 18·7, 21·5 and 21·5° C for alevins, fry and parr respectively; after acclimation at 20° C, mean upper ultimate and incipient values were 26·2, 26·1 and 26·6° C and 20·8, 20·8 and 21·6° C for alevins, fry and parr respectively. The area of the temperature tolerance polygon (expressed as ° C²) for juvenile Arctic charr is amongst the lowest recorded for salmonids; being 409, 439 and 461° C² for alevins, fry and parr respectively. These low values are due to lower upper tolerance limits, not high lower tolerance limits; the latter being close to 0° C (<1°C for parr and fry, <0·3° C for alevins) at all acclimation temperatures. Arctic charr are therefore amongst the least resistant of salmonids to high temperatures but probably the most resistant to low temperatures.     

Influence of salinity on the migration of postlarval and juvenile flounder Pleuronectes flesus L. in a gradient experiment

The behaviour of the flounder Pleuronectes flesus was observed in an experimental aquarium that consisted of five connected units with decreasing salinity from 20 to 15, 10, 5 and 0·5. This experimental aquarium was highly effective for studying behaviour in salinity gradients, because the gradient was relatively stable. After 4 days of observation, significantly more flounder were found in water with a salinity of 0·5, indicating a preference for fresh water. The total length of the flounders ranged from 7·5 to 21 mm. The majority of larvae had already started eye‐migration, however, the longer specimens had completed metamorphosis. The migration towards low salinities was observed to increase with ontogenetic development.     

A one-year investigation of the relationship between serum GH levels and the growth of F4 transgenic and non-transgenic common carp Cyprinus carpio

It has been demonstrated that growth hormone (GH) transgenic fish often posses a trait for fast growth. Here, we investigated the growth of F₄'all-fish' GH transgenic carp Cyprinus carpio and their serum GH levels for a year. The results showed that F₄ all-fish GH transgenic carp were significantly larger in body mass ( c . two-fold, P < 0·001) and body length ( c . 1·3 fold, P < 0·001), compared with the non-transgenic group. The discrepancy of serum GH levels between the transgenic carp group and control group is 54 fold, when the water temperature was 12–34° C. When the water temperature decreased to 3·5° C in January, the discrepancy was 256 fold. The serum GH level of the transgenic group was relatively constant, while that of control varied greatly based on month and water temperature. The changes of growth rates between the transgenic group and the control group were similar for a year. Taken together, the results indicated that F₄ all-fish GH transgenic carp had not only higher and constant serum GH levels but also a significant fast-growing effect, compared with the control. To our knowledge, this is the first report on a one-year investigation of growth trait and serum growth hormone level in F₄ all-fish GH transgenic carp.     

Osmoregulation during the development of glass eels and elvers

Drinking rates in glass eels and elvers of the European eel increased with environmental acclimation salinity from 0·07±0·02 (FW) to 0·70±0·09 μl g-¹ h-¹ (SW) at month 1 and from 1·12±0·42 (FW) to 12·85±1·05 ± l g-¹ h-¹ (SW) at month 5. Drinking rates increased with time in both FW and SW groups. FW acclimated eels when challenged acutely with SW increased drinking rate rapidly immediately upon transfer (0–15 min) and the magnitude of this response increased with developmental time from month 1 to month 5.     

Early development of the skull of Sander lucioperca (L.) (Teleostei: Percidae) relating to growth and mortality

The early osteological development of the skull (chondrocranium and osteocranium) of the pikeperch Sander lucioperca was studied. Specimens were reared at two temperatures, 15·5 and 18·0° C, from hatching until 47 and 43 days after fertilization (DAF), respectively. The skeletal elements characteristic for the different developmental stages were the same at both rearing temperatures, but pikeperch reared at 15·5° C reached the developmental stages later. The formation of the functional complexes, the neurocranium, jaws and suspensorium, branchial basket and hyoid arch, was evaluated chronologically. The focus was on skull development during several functional changes: at hatching, at the shift from endogenous to mixed feeding, the shift to exclusively exogenous feeding and upon reaching the final prey-capture mechanism. Growth in total length differed between fishes reared at the two temperatures, except during a phase of very slow growth from the end of the embryonic stage until the second larval stage. The latter phase, in which most of the bony elements of the viscerocranium started to form, was marked by high mortality. When exogenous feeding began, the growth rates at both temperatures increased distinctly and the first bony elements were formed in the neurocranium. Specimens reared at 18·0° C grew continuously, but those at 15·5° C showed a second period of slow growth and high mortality. Fish reared at 18·0° C reached the successive larval stages distinctly earlier than fish reared at 15·5° C.     

Characteristics of sperm of polyploid Prussian carp Carassius gibelio

Wild-captured 16 diploid, five triploid and one tetraploid Prussian carp Carassius gibelio males produced motile haploid, aneuploid (1·5n) and haploid to aneuploid (> 2n) sperm, respectively, in similar concentration and with the lowest percentage of live spermatozoa in sperm for the tetraploid male (mean ± s . d . 83·03 ± 1·76%; P < 0·05) compared to diploid and triploid males (97·37 ± 1·11% and 96·70 ± 1·45%; P > 0·05).     

Age, growth and cohort composition of 0+ carp in the River Murray, Australia

The age, growth and cohort composition of young-of-the-year (0+) carp, Cyprinus carpio from the River Murray in South Australia were investigated. Daily otolith microincrement formation was validated for the first 5 weeks of life in tetracycline-marked, laboratory-reared fish. Estimation of hatching dates from otolith microincrement counts corroborated the validation method and revealed two major peaks of spawning activity in October and in November. Two main cohorts of carp were distinguished, each consisting of several subcohorts showing variable growth rates. A simple linear regression and a logistic curve best described growth in length and weight, respectively, of wild larvae and juveniles. Two breakpoints, at 16·8 and 26·9 mm L_s , were identified in the length—weight relationship, depending on the procedure followed in fitting a piecewise regression model to the log-transformed variables. The insertion of an additional step of development in the larva period of the early ontogeny of carp is proposed.     

Effects of crowding and availability of food on growth rate of fry in the European and Chinese races of the common carp

Fry of the European and Chinese races of the common carp and interracial crossbred fry were grown together in a series of ponds for 28 days after hatching. The degree of crowding and the amount of available natural food were intentionally varied in these experimental ponds. This resulted in a large variation in mean growth between ponds, ranging from 0·1 to 5·2 g per fish during the 28 days growth period. Under conditions of very slow growth, resulting from severe crowding and lack of natural food, fry of the Chinese carp grew several times faster than European carp. At lower densities and when natural food was more abundant, resulting in a faster rate of growth, this difference between the two races disappeared. Crossbred fry between the Chinese and European carp grew faster than either of their parents under all conditions tested.     

Hypoxia, low salinity and lowered temperature reduce embryo survival and hatch rates in black bream Acanthopagrus butcheri (Munro, 1949)

Embryo survival and hatch rates were measured in black bream Acanthopagrus butcheri exposed to different treatments of dissolved oxygen: hypoxic and normoxic, three salinities: 15, 23 and 35 and two temperatures: 16 and 20° C. Hypoxic conditions (50% saturation) reduced 1 day embryo survival by up to 15% ( P < 0·05) compared to embryos held in normoxic (>80% saturation) conditions. Temperature had no effect on the survival of embryos in these treatments, however, lowered salinity significantly reduced embryo survival at 20° C, but not at 16° C. Mean hatch rates were reduced by 10–28% in hypoxic treatments ( P < 0·05) and lowered salinity treatments ( P < 0·05). Hatching was delayed by up to 24 h at 16° C and very low (or zero) hatching occurred in hypoxic treatments at salinities of 15 and 23. These results confirm that environmental conditions in estuaries are important factors in determining spawning success of black bream and are discussed in relation to global warming and climate change that are likely to alter the physical conditions in southern Australian estuaries.     

A rapid method for determining the quality of gari based on iodine reduction test

A rapid iodine reduction method was developed for predicting the quality of gari. Good quality samples took longer (21·0 ± 4·5s) to reduce iodine than poor quality samples (2·2 ± 0·42 s). There was a strong association between quality and reduction time ( r = 0·97, df = 12) and storage period ( r = 0·99, df = 12) and the reduction time was also dependent on bacterial numbers. Gari stored at low temperatures contained fewer micro-organisms and retained its quality longer than that kept at higher temperatures. The quality of gari can be predicted from iodine reduction times.     

Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ± s . e . fork length, L _F, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method ( C _m). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature ( I _U) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C². In a separate experiment, the I _U of large age 2+ year fish (34·4 ± 0·5 cm L _F) was 1·2 and 0·6° C lower ( P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm L _F) at acclimation temperatures of 16 and 23° C. Using the C _m, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.