Deep-sea habitats are home for a variety of yet poorly known fish species, some of which display specialized life strategies, as is the case of Bythitidae and Zoarcidae. With the purpose of elucidating biological and ecological aspects of representatives of these families in NW Mediterranean waters, a large dataset based on 599 specimens of Cataetyx alleni, 30 C. laticeps and 284 Melanostigma atlanticum captured during the last 30 years within the framework of different research projects was used to address their geographical and bathymetric distribution, population structure, reproduction, trophic ecology, parasitism and enzymatic markers in the Balearic basin. Present outcomes revealed a patchy distribution mostly for M. atlanticum, possibly related to aggregation during reproduction and to the association with specific sediments. For the three species, higher densities occurred in the mainland vs. the insular margin, and a diminishing trend in estimated densities over the last decades was observed for C. alleni and M. atlanticum likely linked to climatic oscillations. Trophic data indicated that the two Cataetyx species inhabit the water-sediment interface and mainly feed on suprabenthic prey, while M. atlanticum inhabits the water column near the bottom preying on pelagic organisms and moving towards the seabed during reproduction. These results were supported by the parasitological assessment, which revealed that parasite communities were moderately diverse and abundant for Cataetyx spp. while being highly depauperate for M. atlanticum. Present outcomes from the Mediterranean Sea confirmed reproduction of C. alleni during autumn-winter and of M. atlanticum during autumn. Spawning of the former species may occur in winter-spring, as suggested by the finding, by the first time, of two females captured in March with fully-developed embryos inside. Levels of enzymatic markers quantified in muscle were provided for C. alleni and M. atlanticum for the first time. The special interactions found between the distribution and biology of Bythitidae and Zoarcidae and the sedimentary bottoms that they inhabit indicates that such conventional habitats are more heterogeneous than it is generally assumed and deserve higher attention for future protection.

深海栖息地是各种鲜为人知的鱼类的家园，其中一些表现出特殊的生活策略，例如 Bythitidae 和 Zoarcidae。为了阐明西北地中海水域中这些科的代表的生物学和生态学方面，一个大型数据集基于过去 30 年在不同研究框架内捕获的599 个Cataetyx alleni、30 C. laticeps和 284 Melanostigma atlanticum标本项目用于解决巴利阿里盆地的地理和水深分布、种群结构、繁殖、营养生态、寄生和酶标记。目前的结果显示主要分布于大西洋 M. atlanticum的不规则分布，可能与繁殖过程中的聚集以及与特定沉积物的关联有关。对于这三个物种，大陆与. 在岛边缘，观察到C. alleni和M. atlanticum 的估计密度在过去几十年中呈递减趋势，这可能与气候振荡有关。营养数据表明，这两种Cataetyx物种栖息在水-沉积物界面，主要以底栖动物为食，而M. atlanticum栖息在靠近底部的水体中，捕食远洋生物并在繁殖期间向海床移动。这些结果得到了寄生​​虫学评估的支持，该评估表明Cataetyx spp 的寄生虫群落具有适度的多样性和丰富性。而对于M. atlanticum 来说却是高度贫乏的。目前地中海的结果证实了C. alleni在秋冬季和M. atlanticum在秋季繁殖。前一种物种的产卵可能发生在冬春季节，正如第一次发现的那样，三月份捕获的两只雌性体内有完全发育的胚胎。为C. alleni提供了在肌肉中量化的酶标记水平和M. atlanticum第一次。在 Bythitidae 和 Zoarcidae 的分布和生物学与它们栖息的沉积底部之间发现的特殊相互作用表明，这些常规栖息地比通常假设的更加异质，值得在未来的保护中给予更多关注。