Evaluation of nematodes and artificial artemia as feed for pacific white shrimp in a biofloc nursery system

The global aquaculture production is growing immensely in all aspects and has already surpassed the output from wild caught fish and shellfish industries. The farming of Penaeus vannamei is one of the biggest contributors to this market. But many early stages of aquaculture depend on the finite and volatile resource Artemia as a live feed. This dependency has been identified as a bottleneck for future growth and sustainability progress. In this experiment, one artificial Artemia product and one nematode species were tested and evaluated in a feeding trial as potential replacements for live Artemia in a zero-water exchange biofloc nursery system. P. vannamei post larvae (PL) were stocked at a density of 60 PL/L in 60-L tanks. They were reared from PL12 – PL33 and fed 8 times per day with a dry feed (DF). Different treatments with four replicates each received a diet supplement of either live nematodes (N), live Artemia (LA), artificial Artemia (AA), or DF (control, C). The PL that received the live diets had nearly twice the survival rate compared to the ones only fed inert diets (N: 94 ± 6%, LA: 91 ± 7%, AA: 53 ± 11%, C: 51 ± 10%). Growth parameters were slightly better in the two inert diet groups (wet weight: N: 22.5 ± 5 mg, LA: 22.5 ± 5 mg, AA: 35 ± 5.7, C: 35 ± 10; Total length: N: 15.8 ± 3.9 mm, LA: 15.8 ± 3.2, AA: 17.1 ± 5.1 mm, C: 17.3 ± 5.0). No significant differences were detected in survival to salinity stress. In addition, beneficial effects on the biofloc and on the water quality were observed in the live diet groups and their causation should be further investigated. The results show that the nematode species Panagrolaimus sp. (NFS 24-5) can completely replace live Artemia in a co-feeding regime.Nas últimas décadas a produção aquícola global experimentou um imenso crescimento em quantidade, variedade de espécies cultivadas e sistemas de produção. Desde 2014 que a aquicultura ultrapassa a produção mundial de peixes e mariscos capturados. O crescimento sem precedentes da população humana é o principal motor de uma procura crescente de proteína aquática de alta qualidade. O cultivo do crustáceo marinho Penaeus vannamei é um dos maiores contribuintes para este mercado. No entanto as fases iniciais das produções de muitos moluscos e peixes dependem de Artemia como alimento vivo, um recurso finito e volátil. Os cistos de Artemia só podem ser colhidos em algumas regiões do planeta e sua produção está sujeita a grandes flutuações naturais, o que limita sua exploração contínua. A dependência de Artemia por parte da indústria da aquicultura foi identificada como um estrangulamento ao crescimento e progresso do sector. A grande procura de proteína aquática levou a uma enorme pressão sobre muitos recursos naturais, em todos os tipos de ecossistemas aquáticos, desde os oceanos às águas interiores e passando pelos ambientes costeiros. A resposta da aquicultura tem de ser persuasiva no sentido de dar garantias de sustentabilidade, mantendo as suas atividades dentro de limites saudáveis. A obtenção de autonomia relativamente à Artemia poderá simplificar significativamente os processos de alimentação durante as fases larvares e, eventualmente, promover a sustentabilidade da aquicultura em geral. Os produtos artificiais de Artemia já estão comercialmente disponíveis mas sua capacidade de alimentar eficientemente larvas de camarão ainda carece de testes científicos. Mais recentemente, uma espécie de nematode foi identificada como tendo propriedades semelhantes às dos cistos de Artemia: armazenamento a longo prazo em estado desidratado, processo de reidratação simples, tamanho pequeno para fácil ingestão e valor nutricional adequado para larvas de camarão. Além disso, estão disponíveis métodos de produção em massa, sustentáveis e economicamente viáveis, que facilitam sua aplicação comercial. Nesta experiência, um produto artificial de Artemia e uma espécie de nematode foram testados e avaliados num ensaio de alimentação como substitutos potenciais de Artemia viva num sistema de viveiro biofloco sem troca de água. Os sistemas Biofloc dependem do controle de nitrogénio através de processos microbianos que ocorrem dentro do tanque de cultivo, o que reduz substancialmente a renovação de água com o benefício adicional de fornecer proteína bacteriana. As pós-larvas (PL) de P. vannamei foram estabuladas com uma densidade de 60 PL por L em tanques semi-cónicos de 60 L. As larvas foram criadas a partir de PL12 - PL30 e alimentadas 8 vezes por dia com ração seca. Diferentes tratamentos com quatro replicados receberam um suplemento alimentar de nemátodos vivos (N), Artemia viva (LA), Artemia artificial (AA) ou ração seca (controle, C). As PL que receberam as dietas vivas tiveram quase o dobro da taxa de sobrevivência quando comparadas às alimentadas apenas com dietas inertes (N: 94 ± 6%, LA: 91 ± 7%, AA: 53 ± 11%, C: 51 ± 10%). No entanto, os parâmetros de crescimento foram ligeiramente melhores nos dois grupos de dieta inerte (peso húmido: N: 22,5 ± 5 mg, LA: 22,5 ± 5 mg, AA: 35 ± 5,7, C: 35 ± 10; Comprimento total: N: 15,8 ± 3,9 mm, LA: 15,8 ± 3,2, AA: 17,1 ± 5,1 mm, C: 17,3 ± 5,0). O efeito do stress salino não foi significativo. Nos grupos de dieta viva foram observados efeitos benéficos na formulação de bioflocos com reduzida acumulação de sólidos suspensos, totais e voláteis. A dieta de nematode também teve níveis de nitrito significativamente menores, indicando melhor controlo do nitrogénio e parâmetros gerais de qualidade da água. O contexto e a causalidade dessas diferenças devem ser investigados, pois podem ser relevantes para operações de aquicultura usando sistemas de bioflocos. Em conclusão, a experiência verificou que a espécie nematode Panagrolaimus sp. (NFS 24-5) pode substituir completamente Artemia viva num regime de co-alimentação. Os resultados deste estudo de alimentação podem promover a sustentabilidade da criação de camarão por meio de alimentos alternativos, independentes dos recursos finitos de Artemia

String Factorizations Under Various Collision Constraints

In the NP-hard Equality-Free String Factorization problem, we are given a string S and ask whether S can be partitioned into k factors that are pairwise distinct. We describe a randomized algorithm for Equality-Free String Factorization with running time 2^k? k^{?(1)}+?(n) improving over previous algorithms with running time k^{?(k)}+?(n) [Schmid, TCS 2016; Mincu and Popa, Proc. SOFSEM 2020]. Our algorithm works for the generalization of Equality-Free String Factorization where equality can be replaced by an arbitrary polynomial-time computable equivalence relation on strings. We also consider two factorization problems to which this algorithm does not apply, namely Prefix-Free String Factorization where we ask for a factorization of size k such that no factor is a prefix of another factor and Substring-Free String Factorization where we ask for a factorization of size k such that no factor is a substring of another factor. We show that these two problems are NP-hard as well. Then, we show that Prefix-Free String Factorization with the prefix-free relation is fixed-parameter tractable with respect to k by providing a polynomial problem kernel. Finally, we show a generic ILP formulation for R-Free String Factorization where R is an arbitrary relation on strings. This formulation improves over a previous one for Equality-Free String Factorization in terms of the number of variables

Self-Organisation of Neural Topologies by Evolutionary Reinforcement Learning

In this article we present EANT, "Evolutionary Acquisition of Neural Topologies", a method that creates neural networks (NNs) by evolutionary reinforcement learning. The structure of NNs is developed using mutation operators, starting from a minimal structure. Their parameters are optimised using CMA-ES. EANT can create NNs that are very specialised; they achieve a very good performance while being relatively small. This can be seen in experiments where our method competes with a different one, called NEAT, "NeuroEvolution of Augmenting Topologies", to create networks that control a robot in a visual serving scenario

On the Complexity of Community-aware Network Sparsification

Network sparsification is the task of reducing the number of edges of a given graph while preserving some crucial graph property. In community-aware network sparsification, the preserved property concerns the subgraphs that are induced by the communities of the graph which are given as vertex subsets. This is formalized in the $\Pi$-Network Sparsification problem: given an edge-weighted graph $G$, a collection $Z$ of $c$ subsets of $V(G)$ (communities), and two numbers $\ell, b$, the question is whether there exists a spanning subgraph $G'$ of $G$ with at most $\ell$ edges of total weight at most $b$ such that $G'[C]$ fulfills $\Pi$ for each community $C$. Here, we consider two graph properties $\Pi$: the connectivity property (Connectivity NWS) and the property of having a spanning star (Stars NWS). Since both problems are NP-hard, we study their parameterized and fine-grained complexity. We provide a tight $2^{\Omega(n^2+c)} poly(n+|Z|)$-time running time lower bound based on the ETH for both problems, where $n$ is the number of vertices in $G$. The lower bound holds even in the restricted case when all communities have size at most 4, $G$ is a clique, and every edge has unit weight. For the connectivity property, the unit weight case with $G$ being a clique is the well-studied problem of computing a hypergraph support with a minimum number of edges. We then study the complexity of both problems parameterized by the feedback edge number $t$ of the solution graph $G'$. For Stars NWS, we present an XP-algorithm for $t$. This answers an open question by Korach and Stern [Disc. Appl. Math. '08] who asked for the existence of polynomial-time algorithms for $t=0$. In contrast, we show for Connectivity NWS that known polynomial-time algorithms for $t=0$ [Korach and Stern, Math. Program. '03; Klemz et al., SWAT '14] cannot be extended by showing that Connectivity NWS is NP-hard for $t=1$

Similar, but different: gender differences in working time arrangements and the work–life interface

Gender inequities can be partly traced back to gender differences in working time arrangements. In fact, it is established knowledge that women as compared to men are more (less) likely to work part-time (overtime). Based on social role theory, however, we also expect gender differences among part-time and overtime workers, such that women and men differ in why they work part-time or overtime. In a preregistered and highly powered study conducted in Germany (N = 3,844–17,361, depending on the analysis), we observed that, on average, women were more likely than men to work part-time (i.e., fewer than 35 hours per week) because of personal or family obligations. Moreover, in comparison to men, women were less likely to work overtime (i.e., at least two hours per week) to attain additional income, but more likely to work overtime to step in for colleagues. Altogether, people had “gendered” reasons to work certain hours. Furthermore, as people’s paid working time arrangements are intertwined with their lives outside of the workplace, we examined women’s and men’s work–life interface and observed that women (as compared to men) deemed it less acceptable to be available for work-related issues during leisure time. We discuss implications for future theorizing and for practitioners who aim to design work schedules that consider the different lived experiences of women and men