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Temperature modifies the reproductive success of fish, yet, in many species, we lack the information on its role in the early development. In this study, the effect of temperature on the relation between maternal traits (length, age, somatic condition, and muscle lipid and ovarian thyroid hormone concentrations), egg quality (fertilization success, development rate, mortality, and hatching success), and offspring traits (size-at-hatch, yolk sac size, and proportion of malformations) were studied in Baltic herring (Clupea harengus membras) in the northern Baltic Sea. The experiments were conducted at an ambient temperature of 7 °C and at an elevated temperature of 14 °C using 5 to 10 females and 3 replicates per female. The results indicate that elevated temperature may result in a faster developmental rate, a lower early-stage mortality and hatching success, smaller size-at-hatch, a larger yolk sac size, and a higher amount of larval malformations when compared to an ambient temperature. The egg and offspring traits were also associated with the maternal traits, indicating especially that thyroid hormones play a mediating role in the physiological processes. [ABSTRACT FROM AUTHOR]

The trade-off between somatic growth and reproduction in the female Baltic herring Clupea harengus was investigated from 1984 to 2002. During the study period, growth decreased, as a consequence of decreasing salinity and weakening of feeding conditions. Production of muscle and ovarian tissue decreased in repeat spawners, but investment in reproduction took an increasing amount of the total production of new tissues. This suggested that a shift in allocation to reproduction takes precedence over body growth in the reproductive strategy of C. harengus. The process also indicated one possible mechanism leading to dwarf forms in fish populations. [ABSTRACT FROM AUTHOR]

The stomach contents of the herring (Clupea harengus membras L.) from the Bothnian Sea, northern Baltic, were analysed during spring 2011 and 2013. The stomachs were full of Limnocalanus macrurus in May and June, and an improvement in the condition of herring was observed when fish started to feed on this prey. The analyses showed that Limnocalanus is currently an important link between lower trophic levels and Baltic herring in the Bothnian Sea. [ABSTRACT FROM PUBLISHER]

Trends with spawning time in the ovarian weight of the Baltic herring (Clupea harengus membras) were studied from samples collected over the spawning season in 1988–1991, 1997 and 1998 in the Archipelago Sea, northern Baltic. Usually, ovarian weight was related to the size composition of the spawning shoals but there was also variation unrelated with female length. In the latter cases, ovarian weight first decreased in the beginning of the spawning season with decreasing fish length but it then increased again in the middle of the season, irrespective of length. In such years, the piecewise regression analysis suggested a breakpoint for the ovarian weight between the dates 14 June and 30 June. At the later part of the spawning season, ovarian weight was associated with temperature conditions and onset of zooplankton production, which suggests that environmental factors modify the reproductive properties of the herring in the Baltic Sea. [ABSTRACT FROM PUBLISHER]

The spawning bed characteristics of the Baltic herring (Clupea harengus membras L.) were investigated during the spawning season in the Airisto Inlet (Northern Baltic Sea) in SW Finland. Within the area, 46 transects were investigated by scuba diver; 37 transects were randomly selected and 9 were known to be spawning beds. Data on the substratum and vegetation were analysed by principal component analysis and discriminant analysis which revealed 10 parameters describing the spawning beds. Two groups were identified; the first contained most of the known spawning beds as well as those resembling them in many parameter values. These beds were situated near the deepest part of the area and contained broad and rich vegetation zones growing on hard bottoms. Herring eggs were not found on all of these beds, but analysis showed they were all potentially suitable for spawning. The other group consisted of sites with bottoms covered by soft sediments, even near the shore line, with the vegetation zone becoming narrower and poorer in plant species. Only two spawning beds were found in this group. [ABSTRACT FROM PUBLISHER]