Immunohistochemical study of pituitary cells in wild and captive Salminus hilarii (Characiformes: Characidae) females during the annual reproductive cycle

Abstract

Freshwater fish that live exclusively in rivers are at particular risk from fragmentation of the aquatic system, mainly the species that migrate upriver for reproduction. That is the case of Salminus hilarii, an important migratory species currently classified as “almost threatened” in the São Paulo State (Brazil), facing water pollution, dam construction, riparian habitat destruction and environmental changes that are even more serious in this State. Additionally, this species show ovulation dysfunction in captivity. Our studies focused on the identification and distribution of the pituitary cell types in the adenohypophysis of S. hilarii females, including a morphometric analysis that compares pituitary cells from wild and captive broodstocks during the reproductive annual cycle. The morphology of adenohypophysial cells showed differences following the reproductive cycle and the environment. In general, optical density suggested a higher cellular activity during the previtellogenic (growth hormone) and vitellogenic (somatolactin) stages in both environments. Additionally, the nucleus/cell ratio analysis suggested that growth hormone and somatolactin cells were larger in wild than in captive females in most reproductive stages of the annual cycle. In contrast, prolactin hormone showed no variation throughout the reproductive cycle (in both environments). Morphometrical analyses related to reproduction of S. hilarii in different environmental conditions, suggest that somatolactin and growth hormone play an important role in reproduction in teleost and can be responsible for the regulation of associated processes that indirectly affect reproductive status.

Gonadotropins and Growth Hormone Family Characterization in an Endangered Siluriform Species, Steindachneridion parahybae (Pimelodidae): Relationship With Annual Reproductive Cycle and Induced Spawning in Captivity

“…Since there are no tests available for measuring pituitary hormones in the plasma of non‐salmonid species, the methods used are a valid substitute to evaluate pituitary hormones during the annual reproductive cycle in S. parahybae . Similar analyses were performed in other teleost species: C. dimerus (Fiszbein et al, ; Piazza et al, ; Tubert et al, ), S. hilarii (Honji et al, ). Moreover, despite nuclear diameter being a useful tool to analyze neuron activity (Fiszbein et al, ; Piazza et al, ), as no differences in nuclear diameter were observed in this study, the morphometric analysis was based mainly on the OD and the cellular diameter as indicative of higher or lower cellular activity during the reproductive cycle of S. parahybae .…”

“…Mousa and Mousa () observed morphometrical variations in SL cells of Oreochromis niloticus and Mugil cephalus during the reproductive period, with higher synthetic and secretory activity during sexual maturation and spawning, suggesting that SL is involved in some reproductive processes. Furthermore, the larger nuclear area and higher OD observed in vitellogenic S. hilarii females (Honji et al, ) also suggests higher cellular activity during the reproductive period in this species. In this sense, during the annual reproductive cycle of S. parahybae , SL‐producing cells showed a more intense OD at the vitellogenic stage than at the previtellogenic and regression stages, suggesting a possible physiological role of this hormone during the reproductive period in this species as well.…”

“…In this study, SL cells were PAS‐positive and distributed in clusters surrounding the NH. Using the PAS stain method in other teleost fish species has revealed two different SL cell types in the PI region, based on whether they expressed non‐glycosylated (PAS‐negative) or glycosylated SL (PAS‐positive) variants (Rand‐Weaver et al, ; Kaneko, ; Villaplana et al, ; Borella et al, ; Honji et al, , and other studies). Even though all SL cells immunostained with anti‐seabream antisera in the PI region were PAS‐positive and only one ir‐band was identified by WB, the presence in S. parahybae of both SL variants cannot be ruled out.…”

“…Several cytochemical investigations focused on the identification and localization of ADH cells types in teleost species, including representative species of the following orders: Cyprinodontiformes (Batten, ), Osteoglossiformes (Borella et al, ), Perciformes (García‐Ayala et al, ; Villaplana et al, ; Pandolfi et al, ); Clupeiformes (Laiz‐Carrión et al, ), Salmoniformes (Naito et al, ), Siluriformes (Volckaert et al, ), Cypriniformes (Chapman et al, ), Osmeriformes (Saga et al, ), Pleuronectiformes (Einarsdóttir et al, ), and Atheriniformes (Vissio et al, ). Among the reophilic Neotropical species, only S. hilarii (Honji et al, ), S. brasiliensis (Jesus et al, ) and Piaractus mesopotamicus (Borella et al, ), all Characiformes, were previously analyzed, adding for the first time to the list the tropical catfish S. parahybae in this study. Although we found similar distribution and localization patterns for ADH cell types in S. parahybae with other teleost species (Agulleiro et al, ; Kawauchi and Sower, ; Takei and Loretz, ; Levavi‐Sivan et al, ), this is the first detailed and accurate identification of ADH cells in a threatened South American fish species, which exhibits endocrine disorders in captivity, reinforcing the importance of this study.…”

“…Somatolactin function in teleost fish is not yet fully established, since mode of action depends on the species considered (Kaneko, ). Some studies suggested that SL is involved in sexual maturity and smoltification in salmonid species (Rand‐Weaver et al, ; Bhandari et al, ; Onuma et al, ); and in adaptation to background and photoperiod changes (Zhu and Thomas, ; Ayson and Takemura, ); metabolism and acid‐base balance (Kakizawa et al, ; Zhu and Thomas, ), stress response (Rand‐Weaver et al, ), and reproductive physiology in non‐salmonid species (Mousa and Mousa, ; Honji et al, ). Furthermore, environmental variations, such as photoperiod and temperature changes, can influence the SL profile (Vargas‐Chacoff et al, ; Fiszbein et al, ).…”