Field studies describe echinoplutei not only as grazers but also as prey of naturally occurring fish and shellfish larvae. This finding suggests their potential as live feed in aquaculture. This paper reports on consistent spawnings of the captive sea urchin Paracentrotus lividus (Lamarck 1816) (Echinodermata: Echinoidea) throughout the year using diets of plant origin (yellow maize and/or dried seaweed) with fixed environmental conditions equivalent to field conditions during late spring (14 h of daily illumination and 18 °C of temperature). Broodstock maturation without unwanted spontaneous spawnings was achieved in two ways: extending the natural season of reproduction and inducing out-of-season wild specimens to mature. Controlled spawnings of captive sea urchins were induced every month of the year by KCl 0.5 M injections. The diet maize/seaweed combination gave the best results (79% of the tested urchins) in terms of consistent large spawnings throughout the year, followed by the pure maize diet (50%) and the pure seaweed diet (36%). When out-of-season wild sea urchins were induced to maturation, the majority (72%) of tested individuals required at least 60 days to spawn under KCl injection when fed the combination diet. The results demonstrate the feasibility of producing larval P. lividus in that high numbers of fertilized eggs (up to 5 million per female) can be obtained year round. The main limitation of exploiting P. lividus as planktonic feed seems to be the mortality of broodstock after injection with 1 ml KCl 0.5 M, which prevents reutilization. The 1-month post-injection survival rate was 30 ± 8% (mean ± SE). All surviving sea urchins spawned again after re-injection 1 month later, with a 1-month survival rate of 29%. Des études in situ décrivent les larves d'échinodermes non seulement comme brouteuses mais aussi comme proies de larves de poissons, crustacés, mollusques. Ce qui laisse présager de leur potentialité en aquaculture, en tant qu'aliment vivant. Nous présentons ici la reproduction tout au long d'une année de l'oursin violet en captivité Paracentrotus lividus (Lamarck 1816) (Echinodermata: Echinoidea) nourri d'aliments d'origine végétale (maïs et/ou graines séchées) en conditions environnementales contrôlées équivalentes à celles observées in situ durant le printemps (14 h d'éclairage et une température de 18 °C). La maturation des géniteurs sans ponte spontanée a été obtenue selon 2 procédés: en étendant la saison de reproduction et en induisant des spécimens sauvages à atteindre leur maturité sexuelle hors saison. Des pontes contrôlées d'oursins ont été induites chaque mois de l'année par injections de KCl 0.5 M. Le régime alimentaire combinant maïs/algues a donné les meilleurs résultats (79 % des oursins), en terme de pontes importantes tout au long de l'année, suivi par un aliment constitué de maïs (50 % des oursins) et d'algues (36 % des oursins). Lorsque l'induction de la maturation d'oursins sauvages a été effectuée, la majorité des oursins (72 %) testés ont demandé 60 jours au moins pour pondre sous injection de KCl et nourris du régime alimentaire mixte. Les résultats démontrent la faisabilité de produire des larves de P. lividus d'un grand nombre d'œufs fertilisés (jusqu'à 5 millions par femelle) qui peuvent être obtenus tout au long de l'année. La principale limite à l'exploitation de P. lividus en tant que nourriture planctonique semble être la mortalité des oursins reproducteurs après l'injection de 1 ml KCl 0.5 M. Le taux de survie des oursins, un mois après injection, était de 30 ± 8 % (mean ± SE). Tous les oursins survivants ont pondu à nouveau après ré-injection un mois plus tard, avec un taux de survie de 29 %.

Biological invasions are considered to be one of the leading causes of biodiversity loss worldwide. Freshwater ecosystems are amongst the most biodiverse, containing about 50% of the world’s known fish species but, ironically, are the most invaded ecosystems. In Portuguese freshwaters, there are currently 20 identified non-native fishes, arriving at an unprecedented rate of a new species every two years. A recent non-native is the European catfish Silurus glanis, a top predator native to Central and Eastern Europe, that arrived at the Lower Tagus (Portugal) circa 2006. This study compares the dietary habits of this top predator in two different habitats of the Lower Tagus in order to evaluate its potential impact. The stomach contents of 96 individuals were analyzed, 61 from the lotic environment and 35 from the lentic systems. A total of 66 stomachs contained prey items, 38 from the lotic and 28 from the lentic. Diet varied considerably between habitats, with shrimp and crayfish being the most abundant prey items in the lentic systems and shrimp and fish the most abundant prey items in the lotic section. Tendency to piscivory was observed in large-sized individuals. Overall, the findings in this study provide the first evidence of the potential impacts of European catfish through predation on the fish communities.

The introduction of non-native species is recognized as a major threat to biodiversity, particularly in freshwater ecosystems. Pikeperch Sander lucioperca, is a recent invader to Portugal, primarily providing commercial and angling interest. The aim of this work was to study the diet of this top predator across Portuguese basins and to evaluate its potential impact on recipient ecosystems. In total, 256 pikeperch stomachs from seven basins were examined, of which 88 (n = 34%) were empty. Pikeperch diet was dominated by R. rutilus, M. salmoides and Diptera in northern populations, while A. alburnus, P. clarkii and Atyidae were important prey in more humid highlands. Variation in diet was most strongly linked to latitude and ontogeny, with both size classes showing signs of cannibalism. The population niche breadth remained low and was accompanied by higher individual diet specialization, particularly in northern populations. Pikeperch dietary patterns denoted an opportunistic ability to use locally abundant prey in each ecosystem, and was size dependent, with larger individuals becoming more piscivores, causing a higher impact in the lotic systems. This first perspective about the pikeperch diet presents a very broad view of the feeding traits of this non-native predator across Portugal, being very important to deepen our knowledge about the impact of these introduced piscivores.

It is globally recognized that freshwater anglers can have a decisive role in promoting fish introductions. The aim of this study was to analyze freshwater anglers’ actions and perceptions regarding fish introductions, comparing two distinct situations, one with recently arrived non-natives fishes and another with older fish introductions, using the Iberian Peninsula as a case study. To achieve this goal, a bilingual survey was implemented on-line in Portugal and Spain and in person (direct inquiries) in two Iberian regions: Lower Ebro (older fish introductions) in Spain; and Lower Tagus (recent fish introductions) in Portugal. Results showed spatial differences in perceptions and actions, namely about the target species, awareness of the impact of non-native fishes, fish introductions reported and proportion of anglers that wanted new fish species. In the Ebro river there is a high percentage of foreign anglers, higher awareness of fish introduction impact and lower introduction rates reported than in the Tagus river. However, popularity of non-native species like European catfish, was higher in the Ebro. In general, although risk behaviors such as use of fish as life bait was of low prevalence for both countries (approx. 5%), it corresponds to large numbers of fish being introduced. Our conservative estimates revealed 273,600 events of bait discharge per year. Regarding the intentional introductions, we estimated a total of 140,000 intentional introduction (illegal) events per year. These findings may help to improve monitoring, awareness and fisheries management programs led by governmental agencies. Graphical abstract