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A full-length complementary (c) DNA encoding ultraviolet ( UV)-sensitive opsin ( sws1) was isolated from the retina of the Japanese sardine Sardinops melanostictus. The sws1 phylogenetic tree showed a sister group relationship with the Cypriniformes, following the ray-finned fish phylogeny. By expressing reconstituted opsin in vitro, it was determined that the maximum absorbance spectrum ( λmax) of sws1 is around 382 nm, being intermediate in position between two subtypes of sws1 pigment that are UV sensitive ( λmax = 355-380 nm) and violet sensitive ( λmax = 388-455 nm), which have been reported to date. The ocular media transmitted >20% transmittance of light in the range of 360-600 nm. In situ hybridization analyses revealed that sws1 messenger (m) RNA is localized in a central single cone surrounded by four double cones in a square mosaic. The square mosaic occupies the ventro-temporal quadrant of the retina and the in situ hybridization signals were dominant in this area suggesting that the fish may use UV vision when looking upward. Based on these results, considerable significances of potential UV sensitivity, in relation to characteristic habits of S. melanostictus, are discussed. [ABSTRACT FROM AUTHOR]

Whether fluctuation in density influenced the growth and maturation variables of three aggregated cohorts (fish born during the 1986-1993, 1996-2003 and 2004-2008 periods) of Pacific sardine Sardinops sagax caeruleus collected off the Californian coast from 2004 to 2010 was investigated. Using a von Bertalanffy mixed-effects model with aggregated cohorts as covariates, estimated growth rate significantly covaried with aggregated cohorts. Growth rate ( K) was modelled as a fixed effect and estimated to be 0·264 ± 0·015 (± s.e). Statistical contrasts among aggregated cohorts showed that the 1996-2003 cohorts had a significantly lower growth rate than the other two aggregated cohorts. The theoretical age at length zero ( t0) and the standard length at infinity ( LS ∞) were modelled as random effects, and were estimated to be −2·885 ± 0·259 (± s.e) and 273·13 ± 6·533 mm (± s.e). The relation of ovary-free mass at length was significantly different among the three aggregated cohorts, with the allometric coefficient estimated to be 2·850 ± 0·013 (± s.e) for the S. sagax population. The age-at-length trajectory of S. sagax born between 1986 and 2008 showed strong density dependence effects on somatic growth rates. In contrast to the density-dependent nature of growth, the probability to be mature at-size or at-age was not significantly affected by aggregated cohort density. The size and the age-at-50% maturity were estimated to be 150·92 mm and 0·56 years, respectively. Stock migration, natural fluctuations in biomass and removal of older and larger S. sagax by fishing might have been interplaying factors controlling growth parameters during 1986-2010. [ABSTRACT FROM AUTHOR]

This study examined the postprandial metabolism and swimming speed of southern bluefin tuna Thunnus maccoyii when fed sardines Sardinops sagax of either high-lipid and high-energy content or low-lipid and low-energy content. Five groups of two or three T. maccoyii (mean ±s.e. mass = 19·8 ± 0·5 kg, n = 14) were fed either low [2·2% lipid, 5·5 MJ kg−1 gross energy (GE)] or high-lipid (12·9%, 9·2 MJ kg−1 GE) S. sagax. Before feeding, T. maccoyii swam at 0·74 ± 0·03 body lengths s−1 ( n = 5) and their routine metabolic rate was 305 ± 15 mg kg−1 h−1. Swimming speed and metabolic rate of T. maccoyii increased following feeding. Thunnus maccoyii swam 1·3 and 1·8 times faster during digestion of low and high-lipid S. sagax, respectively. Postprandial peak metabolic rate, duration of elevated metabolism and total postprandial metabolic increment were all greater for T. maccoyii that ingested high-lipid S. sagax. When total postprandial increment is represented as a proportion of ingested energy, there was no difference between high and low-lipid meals, equating to between 30 and 35% of ingested energy. It was estimated that increased postprandial swimming costs account for 25 and 46% of the total postprandial metabolic response for low and high-lipid S. sagax meals, respectively. Specific dynamic action (SDA) accounts for c. 20% of ingested energy regardless of S. sagax lipid level. These results confirm that the postprandial metabolic increment of T. maccoyii is greater than most other fish species. Much of the high cost of postprandial metabolic increment can be attributed to increased postprandial swimming costs. For T. maccoyii, it appears that activity and SDA are not independent, which complicates bioenergetic evaluation. High postprandial metabolic costs accentuate the great energetic requirements of T. maccoyii. [ABSTRACT FROM AUTHOR]

Larvae of sardine Sardinops sagax and anchovy Engraulis encrasicolus in the northern Benguela upwelling system were distributed predominantly in waters with dissolved oxygen concentrations >2·0 ml l−1 and oxygen saturations >75%. [ABSTRACT FROM AUTHOR]

The growth–mortality relationship was assessed for larval cohorts of the Japanese sardine Sardinops melanostictus using two new approaches: (1) repeat measures in general linear model (RM-GLMs) and (2) the autoregressive-individual method (AIM). Both methods were compared to the traditional approach in which repeat-measure ANOVA was used to compare the changes in increment width ( WI) at age and otolith radii ( RO) at age between individuals from an original population and survivors. In RM-GLMs, both the WI at age and RO at age ( i.e. at 5, 10, 15 and 20 days) were used as the dependent variables, and the standardized residuals of both regressions RO and age and RO and total length ( LT), age class, and day of the year as independent variables. A significant increase in WI at age and RO at age from younger to older age classes was seen as indicative of growth-dependent selection. In AIM, the RO-at-age relationship for each fish was fitted for the first 20 days, using autoregression, and then the growth traits ( i.e. slopes) between the original cohorts and survivors were compared using ANOVA. In the traditional approach, the WI at age and RO at age for the first 20 days of an original population were compared with those of survivors sampled in later stages. GLMs and traditional approaches supported the growth rate ( i.e. the faster an individual grows, the higher its probability of survival) and bigger is better ( i.e. larger individuals at any given age will have lower probability of mortality than smaller individuals of the same age) mechanisms. Furthermore, AIM showed that individuals from original cohorts had lower otolith growth rates than those from survivors, giving further support for the growth–mortality hypothesis for the larval stage of this clupeid. [ABSTRACT FROM AUTHOR]

Growth patterns of larval sardine Sardinops melanostictus were studied in a coastal nursery area, in southern Japan for four monthly hatch cohorts of larvae (November, December, January and February) for the 2003–2004 and 2004–2005 seasons. Laird–Gompertz models were fitted to each cohort using both total length ( LT)-at-age at capture and mean LT-at-age data derived from backcalculations. In both approaches, the absolute daily growth rates ( GR) and absolute daily growth rates at the inflection point ( GXO) were estimated. In parallel, individual growth rates ( GI) were derived from backcalculated LT ( LB). Growth showed the following general common patterns irrespective of hatch month, season and methods: (1) significant Laird–Gompertz fits, (2) asymptotic growth, (3) a decrease in GR after the inflexion point, except for February for the 2003–2004 season that showed an apparent constant growth pattern, (4) six in eight cohorts showed GXO ranging from 0·8 to 1·2 mm day−1 and (5) a decreasing tendency of GI from 1·75 to 0·24 mm day−1, from first feeding through the first month of larval life. The contrasting pattern between the 2003–2004 and the 2004–2005 seasons were: (1) allometric v. logarithmic (ln) LT and otolith radius relationships, (2) low GXO v. high GXO, (3) high GR v. low GR when growth turned asymptotic, (4) low GXO v. high GXO when monthly hatch cohorts were combined and (5) LB and GI not differing among monthly hatch cohorts. The differences in growth patterns and growth rates between seasons seemed to be linked to the influx of warmer and oligotrophic waters of the Kuroshio Current that triggered an increase of 3° C in the coastal area for the 2003–2004 seasons. In the overall context, however, the high GXO, within cohorts and seasons reported in the current study, suggests that either sea surface temperature (SST) or food availability, or both are in the optimal range of preferences for S. melanostictus larvae. Consequently, nearshore coastal areas seem to be playing an important role as a nursery area for the larval stage of this species. [ABSTRACT FROM AUTHOR]

The behaviour, distribution and abundance of the Pacific sardine Sardinops sagax, detected by acoustics, was studied in relation to the pelagic environmental conditions of water temperature, fluorescence and dissolved oxygen concentration induced by tidal currents in Bahía Magdalena, México (24°32′ N; 112°01′ W). Sampling was along an 18 km long transect covering an area inside the bay (mean depth 20 m), the main entrance to the bay (mean depth 35 m), and the continental shelf (mean depth 100 m). The main entrance to the bay was the most dynamic area along the hydrographic transect, where the Pacific sardines tended to aggregate, probably to feed on the phytoplankton accumulated during the receding tide. With the flood tide, a high-speed tidal current is generated, introducing cool water with low oxygen concentrations into the bay. During the ebb tide, a tidal wave is also formed, but the warm and relatively well oxygenated bay water mass is transported towards the open sea. Acoustic records showed that whatever the tidal current direction (inflow or outflow), no fish schools were detected within the area of more intense tidal current speeds (>120 cm s−1). Visual observations of surface Pacific sardine schools during the flood tide indicate that sardines were out of the transducer signal detection range (<10 m depth), suggesting that Pacific sardines undergo vertical migration, probably to avoid the high water current speed with low dissolved oxygen content. This behaviour may have a relevant effect on the overall hydroacoustic estimation of small pelagic fish abundance in shallower pelagic environments such as this subtropical bay. [ABSTRACT FROM AUTHOR]

Gill raker counts were made on the first gill arch from the larval to adult stages of the California sardine Sardinops caeruleus. A model relating gill raker number (NR) to fish length (LS) was developed and can be described by NR=152 (1−e−0·014(LS−11·4)). [Copyright &y& Elsevier]