Seasonal population dynamics of Lepeophtheirus spinifer and Neobenedenia sp. coinfecting snubnose pompano (Trachinotus blochii) breeders in marine cages in the Philippines.

Studies on the biology and ecology of sea lice are lacking in tropical regions such as in Southeast Asia where finfish cage farming has grown dramatically in the past decades. This study investigated the seasonal population dynamics of ectoparasites infecting captive snubnose pompano (Trachinotus blochii) breeders in marine cages in the Philippines. The pompano breeders were found to be naturally coinfected with caligid copepod Lepeophtheirus spinifer and capsalid monogenean Neobenedenia sp. These breeders were monitored and examined bimonthly (n = 10 per sampling) from September 2017 to May 2018, covering the warm season and cold season in the Philippines. Our results clearly show that L. spinifer population maintain a 100 % prevalence throughout warm and cold seasons however, mean abundance and intensity increased only during the cold months (early November to early March) and displayed an oscillating trend during this period. Highest mean intensity was recorded in early January (221.4 ± 24.6; temperature = 27.5 ± 0.3 °C; salinity = 34.8 ± 0.3 ppt) while the lowest mean intensity was recorded during the warm months dipping to 12.5 ± 1.9 in early May (temperature = 30.5 ± 0.3 °C; salinity = 30.3 ± 0.3 ppt). The prevalence of adult and pre-adult was high throughout the monitoring period at 70-100 % except at the start of summer (late March to early May) for pre-adult (30-90 %). In comparison, the chalimus stages were only observed during the cold months specifically from early November to late January with prevalence of 40-80 %. The highest mean abundance (3.4 ± 0.7) and mean intensity (4.3 ± 0.6) was in early November which coincided with the first peak of the total L. spinifer population. Neobenedenia sp. occurred year-round with no significant changes in the population mean abundance and mean intensity between warm and cold seasons. This study presents comprehensive information on the seasonal population dynamics of L. spinifer and Neobenedenia sp. in the Philippines, providing valuable insights on the ecology of caligid sea louse which is fundamental in the formulation of control and management strategies of these economically significant ectoparasites.

mRNA expression patterns for GH, PRL, SL, IGF-I and IGF-II during altered feeding status in rabbitfish, Siganus guttatus.

Feeding time is a major synchronizer of many physiological rhythms in many organisms. Alteration in the nutritional status, specifically fasting, also affects the secretion rhythms of growth hormone (GH) and insulin-like growth factor-I (IGF-I). In this study, we investigated whether the expression patterns for the mRNAs of GH, prolactin (PRL) and somatolactin (SL) in the pituitary gland, and insulin-like growth factor I and II (IGF-I and IGF-II) in the liver of juvenile rabbitfish (Siganus guttatus) follow a rhythm according to feeding time and whether these hormone rhythms changes with starvation. Hormone mRNA levels were determined by real time PCR. The daily expression pattern for the mRNAs of GH, PRL and SL was not altered whether food was given in the morning (10:00 h) or in the afternoon (15:00 h). The daily GH mRNA expression pattern, however, was affected when food was not available for 3 days. In contrast, the daily expression pattern for IGF-I mRNA reaches its peak at roughly 5-6h after feeding. This pattern, however, was not observed with IGF-II mRNA. During 15-day starvation, GH mRNA levels in starved fish were significantly higher than the control fish starting on the 9th day of starvation until day 15. The levels returned to normal after re-feeding. In contrast to GH, PRL mRNA levels in starved fish were significantly lower than the control group starting on the 6th day of starvation until 3 days after re-feeding. SL mRNA levels were not significantly different between the control and starved group at anytime during the experiment. Both IGF-I and IGF-II mRNA levels in starved group were significantly higher than the control fish on the 3rd and 6th day of starvation. mRNA levels of both IGF-I and II in the starved fish decreased starting on the 9th day of starvation. While IGF-I mRNA levels in the starved group continued to decrease as starvation progressed, IGF-II mRNA levels were not significantly different from the control during the rest of the starvation period. The results indicate that aside from GH and IGF-I, PRL and IGF-II are likewise involved in starvation in rabbitfish.

Changes in mRNA expression of grouper (Epinephelus coioides) growth hormone and insulin-like growth factor I in response to nutritional status.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are key links to nutritional condition and growth regulation in teleost. To understand the endocrine mechanism of growth regulation in grouper, we cloned the cDNAs for grouper GH and IGF-I and examined their mRNA expression during different nutritional status. Grouper GH cDNA is 936 base pairs (bp) long excluding the poly-A tail. It contained untranslated regions of 85 and 231bp in the 5'- and 3'-ends, respectively. It has an open reading frame of 612bp coding for a signal peptide of 17 amino acids (aa) and a mature hormone of 187aa residues. Based on the aa sequence of the mature hormone, grouper GH shows higher sequence identity (>76%) to GHs of perciforms than to GHs of cyprinids and salmonids (53-69%). Grouper preproIGF-I cDNA consisted of 558bp, which codes for 186aa. This is composed of 44aa for the signal peptide, 68aa for the mature peptide comprising B, C, A, and D domains, and 74aa for the E domain. Mature grouper IGF-I shows very high sequence identity to IGF-I of teleost fishes (84-97%) compared to advanced groups of vertebrates such as chicken, pig, and human (80%). Using DNA primers specific for grouper GH and IGF-I, the changes in mRNA levels of pituitary GH and hepatic IGF-I in response to starvation and refeeding were examined by a semi-quantitative RT-PCR. Significant elevation of GH mRNA level was observed after 2 weeks of food deprivation, and increased further after 3 and 4 weeks of starvation. GH mRNA level in fed-controls did not change significantly during the same period. Hepatic IGF-I mRNA level decreased significantly starting after 1 week of starvation until the 4th week. There was no significant change in IGF-I mRNA levels in fed-controls. One week of refeeding can restore the GH and IGF-I mRNA back to its normal levels. Deprivation of food for 1-4 weeks also resulted in cessation of growth and decrease in condition factor.