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.     

Strontium:cakium concentration ratios in otoliths of herring larvae as indicators of environmental histories

Synopsis Elemental analyses, using wave-length dispersive electron microprobe techniques on otoliths from reared Atlantic herring larvae, Clupea harengus, showed trace quantities of strontium relative to that of calcium, and an inverse relationship between Sr/Ca concentration ratios and rearing temperature. These data are consistent with those for coral aragonite, in that there appears to be an inverse temperature effect on physiological incorporation of strontium in the otolith aragonite. Our determinations of Sr/Ca concentration ratios of lab-reared herring larvae showed that the deposition of strontium relative to calcium and the rearing temperature were related, where: T (° C) = −2.955 [Sr/Ca] × 1000 ± 19.172. This principle thus makes it possible to use Sr/Ca concentration ratios in fish otoliths to delineate past temperatures experienced by an individual. Further, combining electron microprobe analyses with scanning electron microscope (SEM) examinations of daily increments in the same otolith makes it possible to reconstruct the temperature history for an individual fish on a time scale of days. An example of the application of the technique to an approximately six-month-old field-caught herring larva is given, and the limitations of the technique are discussed.     

Temporal deposition of incremental and discontinuous zones in the otoliths of Oreochromis niloticus (L.)

Ultrathin sections of otoliths were prepared and studied with the transmission electron microscope. The discontinuous zone starts to grow at night, 3 h before light-on, and is completed a few hours after light-on. The growth of the incremental zone follows immediately afterwards and continues approximately until light-off. There is little material deposited onto the otolith at night before the start of discontinuous zone deposition.     

Age estimation of juvenile European hake Merluccius merluccius based on otolith microstructure analysis: a slow or fast growth pattern?

The main goal of this study was to examine otolith microstructure and to estimate the age and growth of European hake Merluccius merluccius from the eastern Mediterranean Sea. One hundred and twenty‐nine specimens ranging from 102 to 438 mm in total length (L_T) were used. Age estimations were based on the study of the otolith microstructure, which was revealed after grinding both frontal sides of otoliths. The enumerations of the daily growth increments (DGI) as well as their width (W_DGI) measurements were made on calibrated digital images. The number of DGI in otoliths ranged between 163 and 717. Four phases in the W_DGI evolution were distinguished: (1) larval–juvenile pelagic phase, with an increasing trend in W_DGI up to the 60th DGI, (2) settlement phase, with a short‐term deceleration in W_DGI between the 61st and 150th DGI, (3) juvenile demersal phase, characterized by a stabilization of W_DGI from 151st to 400th DGI and (4) adult phase, with a decreasing trend in W_DGI after the 400th DGI. Age, sex and month of formation were found to affect the W_DGI in all phases, with the exception of age at the juvenile demersal phase. The power curve with intercept model described best the relationship of M. merluccius L_T with age (T_DGI), according to Akaike criteria, revealing differences in growth between females [L_T = 65 · 36(T_DGI)^{0 · 40} ? 388 · 55] and males [L_T = 69 · 32(T_DGI)^{0 · 37} ? 352 · 88] for the sizes examined. The mean daily growth rates were 0·61 mm day^?1 for females and 0·52 mm day^?1 for males, resulting in an L_T of 283 and 265 mm at the end of their first year of life. In comparison with previous studies on the Mediterranean Sea, the results of this study showed a greater growth rate, similar to results from tagging experiments and otolith microstructure analyses for M. merluccius in other geographic areas.     

Otolith calcification in Atlantic salmon parr, Salmo salar L. and its relation to photoperiod and calcium metabolism

Otolith calcification in Atlantic salmon parr, Salmo salar , was investigated using a radioisotope of calcium, ⁴⁵Ca. Otolith calcification was found to be entrained to light-dark cycles in salmon parr, calcium accumulation on to otoliths declining at night and resuming at dawn. The decline in Otolith calcification at night coincided with a diel decline in plasma calcium concentration. The influence of extracellular calcium on otolith increment formation was considered by inducing hypocalcemia. Induced hypocalcemia resulted in a short-term net loss of calcium from the otolith. The results are discussed in relation to previous studies of the role of extracellular calcium in otolith formation.     

Effects of food ration and temperature level on the growth of Oreochromis niloticus (L.) and their otoliths

Sub-optimal conditions in terms of maintenance ration and/or low temperature resulted in otolith bands, with distinct microstructural features, in response to each particular condition. Check(s) were not only produced corresponding to the transition from optimal to the sub-optimal conditions but also from sub-optimal to the optimal ones. Daily increment deposition, although faint and narrow, persisted in the otoliths of fish when they were kept at low temperatures and fed on maximum food rations. Observable increments were produced only in the first few days of the period when fish were fed on maintenance rations at the optimal temperature. There were only a few checks formed in the otoliths of fish under the conditions of low temperature and maintenance rations. Restraining fish growth in each of the above sub-optimal conditions boosted the growth of the fish and their otoliths when optimal conditions resumed.     

鳡鱼仔稚鱼耳石的标记和其日轮的确证

用茜素络合物对鳡鱼仔鱼进行了浸泡标记,耳石上能检测到橘红色荧光标记环。100mg/L茜素络合物溶液的标记效果较差;120mg/L和150mg/L溶液浸泡后微耳石的标记率很高,矢耳石和星耳石的标记率低。标记后耳石上的生长轮数与饲养天数间呈一一对应关系,相关方程为:N=0.2663 0.9276D(n=68,r~2=0.9664)。方程的斜率0.9276与1无显著差异,证明生长轮确系日轮。鱼体长与微耳石、矢耳石及星耳石的直径间呈显著的线性关系,相关方程为:BL=66.8723LD 2.7064(n=73,r~2=0.8867),BL=22.7839SD 6.6066(n=49,r~2=0.8525),BL=47.6079AD 3.5660(n=71,r~2=0.9012)。     

Diet and condition of three fish species (Characidae) of the Andean foothills in relation to deforestation

Synopsis I studied effects of deforestation on diet and condition of three characid species; Astyanax zonatus, Knodus gamma, and Prionobrama filigera in small streams in the Ecuadorian Amazon. The best condition of K. gamma was found at sites with low canopy cover, while the best condition of P. filigera was found at sites with high canopy cover. Deforestation changed population structure of A. zonatus by decreasing mean size of individuals, but this was not associated with lower fish condition. A. zonatus was omnivorous, and fed equally on invertebrate and plant food. A. zonatus increased feeding on aquatic food items (filamentous algae and fish scales) in the deforested sites (43%) compared to the forested sites (16%). K. gamma was an omnivorous species with preference for invertebrates. K. gamma was mainly feeding on terrestrial food sources in the forested sites, but switched to equal feeding between terrestrial and aquatic food sources in the deforested sites. P. filigera was an terrestrial insectivore feeder, and no differences in the overall food categories was found between stream groups. In contrast, there were no pronounced difference in the composition of invertebrate taxa in the stomachs of K. gamma between stream groups. However, less empty stomachs were observed among K. gamma in the deforested sites. The stomach contents of P. filigera showed great changes in composition of the predominating prey taxa between stream groups and less empty stomachs were observed among P. filigera in the forested sites. Food availability and utilisation seemed to be of main importance for the condition of these fish. Deforestation seems to favour species with high availability to utilise aquatic food items. In contrast, deforestation seems to have negative effects on species that are specialised on terrestrial invertebrates, and have low capacity to switch between aquatic and terrestrial food items.     

Otolith microstructure pattern in Oreochromis niloticus (L.)

The microstructure of otoliths from young and old Oreochromis niloticus (L.) were studied. Otoliths were prepared histologically except for those from newly hatched fish. Hatching results in the formation of a check in the otoliths, which appeared 1 day later. Other checks are rare in juvenile otoliths but common in adult otoliths. Faint and non-daily increments were observed within the hatching check. After hatching, increments were deposited daily. Sub-daily increments were faint and narrow, they were present in the area along the dorso-ventral axis of the otolith but did not continue into the lateral region. Discontinuous zones in the medial area appeared different from those in the lateral area. New growth centres were not only found in the juvenile fish otoliths, but also in adult fish otoliths.     

Quantitative evaluation of the point method for fish stomach contents analysis

To test the accuracy of the point methods a simulation was conducted using simulated stomachs. Results from seven participants told to analyse the stomachs by the point and percentage methods differed considerably among subjects and from the control.     

Limits for the detection of daily otolith increments in whitefish (Coregonus lavaretus L.) larvae

The formation of daily otolith increments in European lake white-fish was evaluated in the laboratory during 40 days at 4, 6, and 8 °C under limited and ad libitum food supply. Daily increments were easily identified in larvae reared at 8 °C. At 6 °C and, more, at 4 °C, an unstructured perinuclear zone was formed, and daily increments could only be recognized in the light microscope starting from 10 to 35 days after hatching. In some larvae from the 4 °C groups, no increments at all were found. Scanning electron microscopy (SEM) could not improve increment resolution. Only those increments could be viewed by SEM which were visible in the light microscope as well. We conclude that whitefish larvae which experience low (4–6 °C) temperatures during their first weeks of life, hence those which hatch in the lake, cannot be aged by the currently employed preparation techniques.