Notes: Abstract Four parameters were examined in order to define sperm quality in turbot Scophthalmus maximus L., sperm: (1) sperm motility, measured by direct counts of the number of active spermatozoa, expressed as % of total spermatozoa; (2) retention of motility after activation, measured by direct counts, 0–60min after activation, expressed as a % of the initial level of activity; (3) resistance to thermal stress, measured as change in retention of motility, and (4) adenosine phosphate (ATP) concentration, determined for samples of non-activated sperm. The proportion of motile spermatozoa at activation ranged from 34·8% to 97·6% (mean 76·3%) for the individual males tested. Turbot sperm retained on average 52% (range 27–90%) of its initial activity one hour after activation. Sperm samples which were stressed by cooling to –27°C retained only 8·6% (range 0–25%) of initial activity, compared to control samples which retained 49% (range 38–63%) of initial activity. The retention of motility after activation was not significantly related to the initial motility or the levels of ATP. Concentrations of ATP in turbot sperm (mean 0·46mg ATP/106 spermatozoa, equivalent to 9·2nmol ATP/108 spermatozoa) were comparable to those measured in mammals.

Notes: Variation in beach seine catches was examined in two juvenile flatfish populations (Port Erin, Isle of Man and Porto Pirn, Azores) to determine the importance of diel cycles while controlling for tidal rhythmicity. At Port Erin sampling was undertaken at each low water on consecutive days over a 2-week period in May/June and September 1991. There was no periodicity in the catches of plaice (Pleuronectes platessa) in May/June, but in September catches were higher at night. Other flatfish species (Limanda limanda, Pleuronectes flesus, Scophthalmus maximus and S. rhombus) sampled at Port Erin were nocturnal. At Porto Pirn, Azores, fish were sampled over 24 h each month from July 1989 to June 1990 and at each low water over a 2-week period in July 1991. The only flatfish species present was Bothuspodas, which had a diurnal pattern in catches over a 1-year period. Sampling at low water in July gave high catches at both midnight and midday.

Notes: A technique was developed for manipulating egg size of recently fertilized Atlantic herring Clupea harengus embryos. Larvae hatching from eggs with reduced yolk volume were shorter than predicted for the volume of yolk removed. The reduction in both body and yolk mass of hatchlings was less than predicted, partly because larval yolk-sac mass was unaffected by yolk removal.

Notes: The eggs of rainbow smelt were incubated at pH c. 4.5, c. 5.5 and control (c. 6.8) for durations of 2–14 days to assess their vulnerability to acid precipitation. These eggs are likely to be exposed to marked pH depressions during their incubation in small streams owing to run-off from snow melt and spring rains. Survival after 48 h exposure was not related to pH, although longer exposure to low pH significantly decreased survival. The developmental stage at initial exposure was also important in determining survival. Overall egg survival varied from 0–87% at pH c. 4.5,0–89% at pH c. 5.5, and 44–100% at control pH levels, (c. 6.8).

Notes: Vaterite otoliths were sampled from two reared populations (Celtic and Clyde Seas) of juvenile herring Clupea harengus. The crystallography, elemental composition and morphometry were analysed and compared with those of normal aragonite otoliths. The incidence of vaterite otoliths in the juveniles sampled (n = 601) ranged from 7·8% in the Clyde population to 13·9% in the Celtic Sea population, and was 5·5% in the small sample (n = 36) of wild adults examined. In all but one case fish had only one vaterite otolith; the corresponding otolith of the pair was completely aragonite. Although the majority of the juveniles sampled showed craniofacial deformities, there was no link between the skull or jaw malformation and the incidence of vaterite otoliths. All vaterite otoliths had an aragonite inner area, and vaterite deposition began sometime after the age of 90 days. The vaterite otoliths were larger and lighter than their corresponding aragonite partners, and were less dense as a consequence of the vaterite crystal structure. The vaterite areas of the otoliths were depleted in Sr, Na and K. Concentrations of Mn were higher in the vaterite areas. The transition between the aragonite inner areas and the vaterite areas was sharply delineated. Within a small spatial scale (20 μm3) in the vaterite areas, however, there was co-precipitation of both vaterite and aragonite. The composition of the aragonite cores in the vaterite otoliths was the same as in the cores of the normal aragonite otoliths indicating that the composition of the aragonite cores did not seed the shift to vaterite. Vaterite is less dense than aragonite, yet the concentrations of Ca analysed with wavelength-dispersive spectrometry (WDS) were the same between the two polymorphs, indicating that Ca concentrations measured with WDS are not a good indicator of hypermineralized zones with high mineral density. The asymmetry in density and size of the otoliths may cause disruptions of hearing and pressure sensitivity for individual fish with one vaterite otolith, however, the presence of vaterite otoliths did not seem to affect the growth of these laboratory reared juvenile herring.

Notes: Juvenile plaice (Pleuronectes platessa) were studied in Port Erin Bay, Isle of Man, U.K. between September and March 1989/1990 and 1990/1991. Plaice (〉90 mm) were tagged and individual growth rates calculated for the autumn, winter and over-winter time periods. During the study the population of fish 〉90 mm remained fairly stable both within a study season and between years. Autumn growth rates ranged from 0 to 0.39 mm day−1 (mean1989=0.13 mm day−1, mean1990=0.10 mm day −1) and winter 0 to 0.5 mm day−1 (mean1990=0.11 mm day−1 and mean1991=0.17 mm day −1). In general, growth rates were higher at higher mean seasonal temperatures. However, relative growth rate was significantly higher in the colder winter period of 1991 than 1990.

Notes: Wild herring larvae were sampled from the Firth of Clyde, Scotland in 1980 and 1981 to assess the suitability of otolith ageing methods for herring larval studies. The ages and growth rates were estimated directly from otolith ring counts, by comparison of ring counts with the results of validation studies on reared larvae of known age, and by back-calculation. Growth rates based on otolith data were compared with indirect calculations based on length at capture. The assumption of daily ring deposition, even allowing for a period of lag before the initiation of daily ring deposition, led to incorrect predictions for age at yolk-sac absorption, and back-calculations led to overestimated growth rates, indicating that ring deposition does not begin at hatching and that light microscope counts give a rate different from one ring per day in wild herring larvae.

Notes: Salmon embryos, age 48–81 days post-fertilization (dpf), were incubated under three different temperature and photoperiod regimes to test the effects of incubation conditions on otolith ring deposition. Otolith rings were first observed at 50 dpf and certain developmental events were marked by distinct, heavy rings. The rate of ring deposition increased with increasing temperature and exposure to light, ranging from 0·50 to 2·33 rings per day. The possible relation to physiological activity as measured by oxygen consumption is discussed.

Notes: The lengths of newly hatched herring Clupea harengus larvae were generally larger than the lengths of embryos released from eggs on the same day. Over subsequent days, the daily increase in length was higher in groups that were released from the eggs as opposed to groups that hatched naturally. Thus by the end of the hatching period (18 days after fertilization) there were no significant differences in mean lengths.

Notes: The growth and changes in the standard deviation about mean length were measured for sole, Solea solea L., and herring, Clupea harengus L., larvae from crosses of one or two males with one or two females. The sizes of sole larvae did not differ between crosses but the size variation increased faster with age when two females were used. Both maternal and paternal effects were detected for size at hatching in herring, but there was no parental influence on size variation. Size variation in herring larvae declined or was stable during the yolk sac stage and was not affected by the number of parents used for fertilizations.