Jorge Palma

Gastric evacuation and feeding in the gilthead sea bream reared under semi-intensive conditions

Gastric evacuation rates of the gilthead sea bream, Sparus aurata, fed with commercial pelleted food and polychaetes (Nereis diversicolor) were determined under experimental conditions. The estimated gastric evacuation rate for pelleted food was 7.97% h−1, with a total time of digestion of approximately 9 h. The respective values for the natural food were 6.24% h−1, with a total digestion time of approximately 12 h. The daily consumption of fish reared in earth ponds in a semi-intensive aquaculture facility was estimated through 24 h cycles performed between April and August. The daily consumption varied from 18.58 to 31.98 mg g−1. There was a constant increase in the average daily consumption per individual of 1.8–4.6 g (dry weight). During these cycles, samples of stomachs were taken and the contents preserved for further observation. The feeding behaviour of the reared fish was compared with a fish sample caught in the Ria Formosa lagoon. No common species were found between samples. A total of 38 prey were identified, which suggests that the gilthead sea bream is a non-specific predator. Despite the high abundance of natural prey in the ponds, the dependence of sea bream on pelleted food was high.

Developmental stability and genetic heterozygosity in wild and cultured stocks of gilthead sea bream (Sparus aurata)

The present study checks on the validity of the hypothesis that heterozygosity and the fluctuating asymmetry (FA), common measure of the developmental stability, are linked in populations of wild and cultured stocks of Sparus aurata from five countries. Muscle and liver samples were analysed for variation in 26 allozymes and three microsatellite loci. Pectoral fin rays and upper and lower gill rakers of the first branchial arch were counted on the left and on the right sides of each fish. Fluctuating asymmetry existed in the majority of the samples although their values were consistently low, (0·305±0·147), but higher in the cultured samples. The allozyme heterozygosity values were always high, but lower in the cultured samples. The microsatellite DNA analysis produced similar results. Heterozygosity was higher in cultured individuals (except for the Greek samples). These findings seem to be early evidence that the reared samples are losing some genetic variation, especially due to the loss of the rarest alleles (which were present in the wild populations). Genetic drift, probably caused by propagation practices, is most likely responsible for the decrease of the genetic variation. No distinct pattern of geographic separation was identified.

Advances in tagging syngnathids, with the effects of dummy tags on behaviour of Hippocampus guttulatus

Artificial marking and tagging techniques have been used to study movement, population dynamics, behaviour, ecology, survival and growth of at least 25 syngnathid species. External necklace-style tags and injection of visible implant elastomer have been the most used techniques, uniquely identifying hundreds of individual syngnathids to study population dynamics, mortality, behaviour, ecology and growth in at least 13 and 12 species, respectively. Only two studies, both on larger syngnathid species, have tested the use of internal or electronic tags. This new case study reveals that dummy tags, weighing up to 6% of individual body mass, have minimal effect on normal ex situ behaviour of the long-snouted seahorse Hippocampus guttulatus, a smaller syngnathid. In paired aquarium trials, tags did not affect movement, holdfast use or general behavioural state, and only had a short-term effect (1 day) on vertical orientation. Tagged H. guttulatus gained more mass during the 5 day trials, a result which warrants further exploration but indicates that tags did not reduce feeding. This study shows promise for using electronic tagging to study H. guttulatus and similarly sized syngnathids in the wild.

Seahorse (Hippocampinae) population fluctuations in the Ria Formosa Lagoon, south Portugal.

Comparisons of three sets of surveys in the Ria Formosa Lagoon, Portugal, over a 13 year period (2001-2002, 2008-2009 and 2010-2013) revealed significant population fluctuations in at least one of the two seahorse (Hippocampinae) species living there, and that those fluctuations were potentially associated with habitat changes in the lagoon. After a significant decline between the first two survey periods (2001-2002 v. 2008-2009), long-snouted seahorse Hippocampus guttulatus populations increased significantly between 2008-2009 surveys and new 2010-2013 surveys. There were no significant differences in H. guttulatus populations between the 2001-2002 and 2010-2013 surveys. In contrast, there were no significant differences in short-snouted seahorse Hippocampus hippocampus densities among the 16 sites surveyed throughout the three sampling periods, although the ability to detect any change was hampered by the low densities of this species in all time periods. Fluctuations in H. guttulatus densities were positively correlated with the percentage of holdfast coverage, but with none of the other environmental variables tested. These results highlight the importance of holdfast availability in maintaining stable seahorse populations. While population fluctuations are certainly more promising than a consistent downward decline, such extreme fluctuations observed for seahorses in the Ria Formosa Lagoon could still leave these two species vulnerable to any additional stressors, particularly during low density periods.

Flatfish discarding practices in bivalve dredge fishing off the south coast of Portugal (Algarve)

An evaluation of flatfish discards from bivalve dredge fishing on the south coast of Portugal (Algarve) was undertaken through fishing surveys carried out on board a professional dredge fleet. Data collection of the dredge fishery was carried out between November 2000 and February 2002. The data were compared with information gathered from abundance analysis surveys, and analysed independently of the target bivalve species (Chamelea gallina, Donnax trunculus, and Spisula solida). Flatfish and non-flatfish species accounted for 20.1% and 79.9%, respectively, of the by-catch species of the bivalve dredge fishery. Significant differences have been calculated between length composition of flatfish species in the by-catch and in the abundance surveys. This indicates an optimised performance of the bivalve dredge, which catches a small amount of undersized flatfish as by-catch.

Morphometric characters in gilthead sea bream, Sparus aurata, red porgy, Pagrus pagrus and their hybrids (Sparidae)

A morphometric comparison was made between Sparus aurata (n = 88), Pagrus pagrus (n = 38) and their hybrid S. aurata (female) x P. pagrus (male) (n = 81) using 15 morphometric characteristics. The morphometric characteristics of the hybrids were generally intermediate to those of the parental species. However, characteristics related to the body shape (6) were more similar to 5. aurata and those characters related to the head shape (9) were more similar to P. pagrus.